forked from mpusz/mp-units
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||
</li>
|
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|
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<li class="md-nav__item">
|
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<a href="../../../getting_started/faq/" class="md-nav__link">
|
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|
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<span class="md-ellipsis">
|
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FAQ
|
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</span>
|
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|
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</a>
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</li>
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|
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|
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</ul>
|
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</nav>
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<li class="md-nav__item md-nav__item--active md-nav__item--section md-nav__item--nested">
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<input class="md-nav__toggle md-toggle " type="checkbox" id="__nav_3" checked>
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<label class="md-nav__link" for="__nav_3" id="__nav_3_label" tabindex="0">
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<span class="md-ellipsis">
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User's Guide
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<span class="md-nav__icon md-icon"></span>
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</label>
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<nav class="md-nav" data-md-level="1" aria-labelledby="__nav_3_label" aria-expanded="true">
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<label class="md-nav__title" for="__nav_3">
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<span class="md-nav__icon md-icon"></span>
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User's Guide
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</label>
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<ul class="md-nav__list" data-md-scrollfix>
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<li class="md-nav__item">
|
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<a href="../../terms_and_definitions/" class="md-nav__link">
|
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|
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<span class="md-ellipsis">
|
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Terms and Definitions
|
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</span>
|
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|
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|
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</a>
|
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</li>
|
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<li class="md-nav__item md-nav__item--active md-nav__item--nested">
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Framework Basics
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Framework Basics
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|
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|
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<span class="md-ellipsis">
|
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Basic Concepts
|
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</span>
|
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|
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|
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</a>
|
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</li>
|
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|
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<li class="md-nav__item">
|
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<a href="../interface_introduction/" class="md-nav__link">
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<span class="md-ellipsis">
|
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Interface Introduction
|
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</span>
|
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|
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|
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</a>
|
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</li>
|
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<li class="md-nav__item">
|
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<a href="../systems_of_quantities/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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Systems of Quantities
|
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</span>
|
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|
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|
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</a>
|
||
</li>
|
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|
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<li class="md-nav__item">
|
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<a href="../systems_of_units/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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Systems of Units
|
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</span>
|
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|
||
|
||
</a>
|
||
</li>
|
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|
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|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../simple_and_typed_quantities/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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Simple and Typed Quantities
|
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</span>
|
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|
||
|
||
</a>
|
||
</li>
|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../value_conversions/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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Value Conversions
|
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</span>
|
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|
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|
||
</a>
|
||
</li>
|
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|
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|
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|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../character_of_a_quantity/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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Character of a Quantity
|
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</span>
|
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|
||
|
||
</a>
|
||
</li>
|
||
|
||
|
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|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../dimensionless_quantities/" class="md-nav__link">
|
||
|
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|
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<span class="md-ellipsis">
|
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Dimensionless Quantities
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
||
|
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|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../quantity_arithmetics/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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Quantity Arithmetics
|
||
</span>
|
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|
||
|
||
</a>
|
||
</li>
|
||
|
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|
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|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../generic_interfaces/" class="md-nav__link">
|
||
|
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|
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<span class="md-ellipsis">
|
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Generic Interfaces
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
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|
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|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../faster_than_lightspeed_constants/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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Faster-than-lightspeed Constants
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
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|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../the_affine_space/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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The Affine Space
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
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|
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|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../obtaining_metadata/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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Obtaining Metadata
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
||
|
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|
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|
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<li class="md-nav__item md-nav__item--active">
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<input class="md-nav__toggle md-toggle" type="checkbox" id="__toc">
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<label class="md-nav__link md-nav__link--active" for="__toc">
|
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|
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<span class="md-ellipsis">
|
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Text Output
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</span>
|
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|
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|
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<span class="md-nav__icon md-icon"></span>
|
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</label>
|
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<a href="./" class="md-nav__link md-nav__link--active">
|
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|
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<span class="md-ellipsis">
|
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Text Output
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</span>
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|
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|
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</a>
|
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|
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|
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|
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<nav class="md-nav md-nav--secondary" aria-label="Table of contents">
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|
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|
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|
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<label class="md-nav__title" for="__toc">
|
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<span class="md-nav__icon md-icon"></span>
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Table of contents
|
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</label>
|
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<ul class="md-nav__list" data-md-component="toc" data-md-scrollfix>
|
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|
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<li class="md-nav__item">
|
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<a href="#customization-point" class="md-nav__link">
|
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Customization point
|
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</a>
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</li>
|
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|
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<li class="md-nav__item">
|
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<a href="#output-streams" class="md-nav__link">
|
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Output streams
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</a>
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<nav class="md-nav" aria-label="Output streams">
|
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<ul class="md-nav__list">
|
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|
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<li class="md-nav__item">
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<a href="#output-stream-formatting" class="md-nav__link">
|
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Output stream formatting
|
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</a>
|
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|
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</li>
|
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|
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</ul>
|
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</nav>
|
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|
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</li>
|
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|
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<li class="md-nav__item">
|
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<a href="#stdformat" class="md-nav__link">
|
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std::format
|
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</a>
|
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|
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<nav class="md-nav" aria-label="std::format">
|
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<ul class="md-nav__list">
|
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|
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<li class="md-nav__item">
|
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<a href="#grammar" class="md-nav__link">
|
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Grammar
|
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</a>
|
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|
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</li>
|
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|
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<li class="md-nav__item">
|
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<a href="#default-formatting" class="md-nav__link">
|
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Default formatting
|
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</a>
|
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|
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</li>
|
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|
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<li class="md-nav__item">
|
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<a href="#controlling-width-fill-and-alignment" class="md-nav__link">
|
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Controlling width, fill, and alignment
|
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</a>
|
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|
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</li>
|
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|
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<li class="md-nav__item">
|
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<a href="#quantity-value-symbol-or-both" class="md-nav__link">
|
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Quantity value, symbol, or both?
|
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</a>
|
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|
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</li>
|
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|
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<li class="md-nav__item">
|
||
<a href="#quantity-value-formatting" class="md-nav__link">
|
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Quantity value formatting
|
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</a>
|
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|
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</li>
|
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|
||
<li class="md-nav__item">
|
||
<a href="#unit-symbol-formatting" class="md-nav__link">
|
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Unit symbol formatting
|
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</a>
|
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|
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</li>
|
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|
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</ul>
|
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</nav>
|
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|
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</li>
|
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|
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</ul>
|
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|
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</nav>
|
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|
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</li>
|
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|
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|
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|
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|
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</ul>
|
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</nav>
|
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|
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</li>
|
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|
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|
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|
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|
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|
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|
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|
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|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item md-nav__item--nested">
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<span class="md-ellipsis">
|
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Defining Systems
|
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</span>
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<span class="md-nav__icon md-icon"></span>
|
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</label>
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<nav class="md-nav" data-md-level="2" aria-labelledby="__nav_3_3_label" aria-expanded="false">
|
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<label class="md-nav__title" for="__nav_3_3">
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<span class="md-nav__icon md-icon"></span>
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Defining Systems
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</label>
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<ul class="md-nav__list" data-md-scrollfix>
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|
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<a href="../../defining_systems/introduction/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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Introduction
|
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</span>
|
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|
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|
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</a>
|
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</li>
|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../../defining_systems/isq/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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International System of Quantities (ISQ)
|
||
</span>
|
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|
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|
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</a>
|
||
</li>
|
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|
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|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../../defining_systems/si/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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International System of Units (SI)
|
||
</span>
|
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|
||
|
||
</a>
|
||
</li>
|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../../defining_systems/strong_angular_system/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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Strong Angular System
|
||
</span>
|
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|
||
|
||
</a>
|
||
</li>
|
||
|
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|
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|
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|
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|
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|
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|
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|
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|
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<li class="md-nav__item">
|
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<a href="../../defining_systems/natural_units/" class="md-nav__link">
|
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|
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|
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<span class="md-ellipsis">
|
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Natural Units
|
||
</span>
|
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|
||
|
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</a>
|
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</li>
|
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|
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|
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|
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|
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</ul>
|
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</nav>
|
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|
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</li>
|
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|
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|
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|
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|
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|
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|
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|
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|
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|
||
|
||
|
||
|
||
|
||
|
||
|
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|
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|
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|
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|
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<li class="md-nav__item md-nav__item--nested">
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<label class="md-nav__link" for="__nav_3_4" id="__nav_3_4_label" tabindex="0">
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<span class="md-ellipsis">
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Use Cases
|
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</span>
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<span class="md-nav__icon md-icon"></span>
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</label>
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<nav class="md-nav" data-md-level="2" aria-labelledby="__nav_3_4_label" aria-expanded="false">
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<span class="md-nav__icon md-icon"></span>
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Use Cases
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</label>
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<ul class="md-nav__list" data-md-scrollfix>
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<li class="md-nav__item">
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<a href="../../use_cases/pure_dimensional_analysis/" class="md-nav__link">
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<span class="md-ellipsis">
|
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Pure Dimensional Analysis
|
||
</span>
|
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|
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|
||
</a>
|
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</li>
|
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<li class="md-nav__item">
|
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<a href="../../use_cases/working_with_legacy_interfaces/" class="md-nav__link">
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<span class="md-ellipsis">
|
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Working with Legacy Interfaces
|
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</span>
|
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|
||
|
||
</a>
|
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<h1 id="text-output">Text Output<a class="headerlink" href="#text-output" title="Permanent link">¶</a></h1>
|
||
<p>Besides providing dimensional analysis and units conversions, the library also tries hard to print
|
||
any quantity in the most user-friendly way.</p>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">Note</p>
|
||
<p>The library does not provide a text output for quantity points, as printing just a number and a unit
|
||
is not enough to adequately describe a quantity point. Often an additional postfix is required.</p>
|
||
<p>For example, the text output of <code>42 m</code> may mean many things and can also be confused with an output
|
||
of a regular quantity. On the other hand, printing <code>42 m AMSL</code> for altitudes above mean sea level is
|
||
a much better solution, but the library does not have enough information to print it that way by itself.</p>
|
||
</div>
|
||
<h2 id="customization-point">Customization point<a class="headerlink" href="#customization-point" title="Permanent link">¶</a></h2>
|
||
<p>The <a href="../appendix/references.md#SIBrochure">SI Brochure</a> says:</p>
|
||
<div class="admonition quote">
|
||
<p class="admonition-title">SI Brochure</p>
|
||
<p>The numerical value always precedes the unit and a space is always used to separate the unit from
|
||
the number. ... The only exceptions to this rule are for the unit symbols for degree, minute and
|
||
second for plane angle, <code>°</code>, <code>′</code> and <code>″</code>, respectively, for which no space is left between the
|
||
numerical value and the unit symbol.</p>
|
||
</div>
|
||
<p>To support the above, the library exposes <code>space_before_unit_symbol</code> customization point. By default,
|
||
its value is <code>true</code> for all the units, so the space between a number and a unit will be present in the
|
||
output text. To change this behavior, we have to provide a partial specialization for a specific unit:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-0-1"><a id="__codelineno-0-1" name="__codelineno-0-1" href="#__codelineno-0-1"></a><span class="k">template</span><span class="o"><></span>
|
||
</span><span id="__span-0-2"><a id="__codelineno-0-2" name="__codelineno-0-2" href="#__codelineno-0-2"></a><span class="kr">inline</span><span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="n">space_before_unit_symbol</span><span class="o"><</span><span class="n">non_si</span><span class="o">::</span><span class="n">degree</span><span class="o">></span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">false</span><span class="p">;</span>
|
||
</span></code></pre></div>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">Note</p>
|
||
<p>The above works only for <a href="#default-formatting">the default formatting</a>. In case we provide our own
|
||
format specification (i.e. <code>std::format("{:%Q %q}", q)</code>), the library will always obey this
|
||
specification for all the units (no matter of what is the actual value of the
|
||
<code>space_before_unit_symbol</code> customization point) and the separating space will always be present
|
||
in this case.</p>
|
||
</div>
|
||
<h2 id="output-streams">Output streams<a class="headerlink" href="#output-streams" title="Permanent link">¶</a></h2>
|
||
<div class="admonition tip">
|
||
<p class="admonition-title">Tip</p>
|
||
<p>The output streaming support is opt-in and can be enabled by including the <code><mp-units/ostream.h></code>
|
||
header file.</p>
|
||
</div>
|
||
<p>The easiest way to print a quantity is to provide its object to the output stream:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-1-1"><a id="__codelineno-1-1" name="__codelineno-1-1" href="#__codelineno-1-1"></a><span class="k">using</span><span class="w"> </span><span class="k">namespace</span><span class="w"> </span><span class="nn">mp_units</span><span class="p">;</span>
|
||
</span><span id="__span-1-2"><a id="__codelineno-1-2" name="__codelineno-1-2" href="#__codelineno-1-2"></a><span class="k">using</span><span class="w"> </span><span class="k">namespace</span><span class="w"> </span><span class="nn">mp_units</span><span class="o">::</span><span class="nn">si</span><span class="o">::</span><span class="nn">unit_symbols</span><span class="p">;</span>
|
||
</span><span id="__span-1-3"><a id="__codelineno-1-3" name="__codelineno-1-3" href="#__codelineno-1-3"></a><span class="k">using</span><span class="w"> </span><span class="k">namespace</span><span class="w"> </span><span class="nn">mp_units</span><span class="o">::</span><span class="nn">international</span><span class="o">::</span><span class="nn">unit_symbols</span><span class="p">;</span>
|
||
</span><span id="__span-1-4"><a id="__codelineno-1-4" name="__codelineno-1-4" href="#__codelineno-1-4"></a>
|
||
</span><span id="__span-1-5"><a id="__codelineno-1-5" name="__codelineno-1-5" href="#__codelineno-1-5"></a><span class="k">const</span><span class="w"> </span><span class="n">QuantityOf</span><span class="o"><</span><span class="n">isq</span><span class="o">::</span><span class="n">speed</span><span class="o">></span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">v1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">avg_speed</span><span class="p">(</span><span class="mf">220.</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">km</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">h</span><span class="p">);</span>
|
||
</span><span id="__span-1-6"><a id="__codelineno-1-6" name="__codelineno-1-6" href="#__codelineno-1-6"></a><span class="k">const</span><span class="w"> </span><span class="n">QuantityOf</span><span class="o"><</span><span class="n">isq</span><span class="o">::</span><span class="n">speed</span><span class="o">></span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">v2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">avg_speed</span><span class="p">(</span><span class="mf">140.</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">mi</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">h</span><span class="p">);</span>
|
||
</span><span id="__span-1-7"><a id="__codelineno-1-7" name="__codelineno-1-7" href="#__codelineno-1-7"></a><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">v1</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="sc">'\n'</span><span class="p">;</span><span class="w"> </span><span class="c1">// 110 km/h</span>
|
||
</span><span id="__span-1-8"><a id="__codelineno-1-8" name="__codelineno-1-8" href="#__codelineno-1-8"></a><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">v2</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="sc">'\n'</span><span class="p">;</span><span class="w"> </span><span class="c1">// 70 mi/h</span>
|
||
</span></code></pre></div>
|
||
<p>The text output will always print the <a href="../../../appendix/glossary/#quantity-value">value of a quantity</a>
|
||
typically followed by a space and then the symbol of a <a href="../../../appendix/glossary/#unit">unit</a>
|
||
associated with this quantity.</p>
|
||
<div class="admonition important">
|
||
<p class="admonition-title">Important</p>
|
||
<p>Remember that when we deal with a quantity of an "unknown" <code>auto</code> type, it is a good practice
|
||
to always <a href="../value_conversions/#value-conversions">convert the unit to the expected one</a>
|
||
before passing it to the text output:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-2-1"><a id="__codelineno-2-1" name="__codelineno-2-1" href="#__codelineno-2-1"></a><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">v1</span><span class="p">.</span><span class="n">in</span><span class="p">(</span><span class="n">km</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">h</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="sc">'\n'</span><span class="p">;</span><span class="w"> </span><span class="c1">// 110 km/h</span>
|
||
</span><span id="__span-2-2"><a id="__codelineno-2-2" name="__codelineno-2-2" href="#__codelineno-2-2"></a><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">v1</span><span class="p">.</span><span class="n">force_in</span><span class="p">(</span><span class="n">m</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="sc">'\n'</span><span class="p">;</span><span class="w"> </span><span class="c1">// 30.5556 m/s</span>
|
||
</span></code></pre></div>
|
||
</div>
|
||
<h3 id="output-stream-formatting">Output stream formatting<a class="headerlink" href="#output-stream-formatting" title="Permanent link">¶</a></h3>
|
||
<p>Only basic formatting can be applied for output streams. It includes control over width, fill,
|
||
and alignment:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-3-1"><a id="__codelineno-3-1" name="__codelineno-3-1" href="#__codelineno-3-1"></a><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"|"</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">setw</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"|</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span><span class="w"> </span><span class="c1">// | 123 m|</span>
|
||
</span><span id="__span-3-2"><a id="__codelineno-3-2" name="__codelineno-3-2" href="#__codelineno-3-2"></a><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"|"</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">setw</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">left</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"|</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span><span class="w"> </span><span class="c1">// |123 m |</span>
|
||
</span><span id="__span-3-3"><a id="__codelineno-3-3" name="__codelineno-3-3" href="#__codelineno-3-3"></a><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"|"</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">setw</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">setfill</span><span class="p">(</span><span class="sc">'*'</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"|</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span><span class="w"> </span><span class="c1">// |123 m*****|</span>
|
||
</span></code></pre></div>
|
||
<h2 id="stdformat"><code>std::format</code><a class="headerlink" href="#stdformat" title="Permanent link">¶</a></h2>
|
||
<div class="admonition tip">
|
||
<p class="admonition-title">Tip</p>
|
||
<p>The text formatting facility support is opt-in and can be enabled by including the
|
||
<code><mp-units/format.h></code> header file.</p>
|
||
</div>
|
||
<p>The <strong>mp-units</strong> library provides custom formatters for <code>std::format</code> facility which allows
|
||
fine-grained control over what and how it is being printed in the text output.</p>
|
||
<h3 id="grammar">Grammar<a class="headerlink" href="#grammar" title="Permanent link">¶</a></h3>
|
||
<div class="language-text highlight"><pre><span></span><code><span id="__span-4-1"><a id="__codelineno-4-1" name="__codelineno-4-1" href="#__codelineno-4-1"></a>units-format-spec ::= [fill-and-align] [width] [units-specs]
|
||
</span><span id="__span-4-2"><a id="__codelineno-4-2" name="__codelineno-4-2" href="#__codelineno-4-2"></a>units-specs ::= conversion-spec
|
||
</span><span id="__span-4-3"><a id="__codelineno-4-3" name="__codelineno-4-3" href="#__codelineno-4-3"></a> units-specs conversion-spec
|
||
</span><span id="__span-4-4"><a id="__codelineno-4-4" name="__codelineno-4-4" href="#__codelineno-4-4"></a> units-specs literal-char
|
||
</span><span id="__span-4-5"><a id="__codelineno-4-5" name="__codelineno-4-5" href="#__codelineno-4-5"></a>literal-char ::= any character other than '{' or '}'
|
||
</span><span id="__span-4-6"><a id="__codelineno-4-6" name="__codelineno-4-6" href="#__codelineno-4-6"></a>conversion-spec ::= '%' units-type
|
||
</span><span id="__span-4-7"><a id="__codelineno-4-7" name="__codelineno-4-7" href="#__codelineno-4-7"></a>units-type ::= [units-rep-modifier] 'Q'
|
||
</span><span id="__span-4-8"><a id="__codelineno-4-8" name="__codelineno-4-8" href="#__codelineno-4-8"></a> [units-unit-modifier] 'q'
|
||
</span><span id="__span-4-9"><a id="__codelineno-4-9" name="__codelineno-4-9" href="#__codelineno-4-9"></a>units-rep-modifier ::= [sign] [#] [precision] [L] [units-rep-type]
|
||
</span><span id="__span-4-10"><a id="__codelineno-4-10" name="__codelineno-4-10" href="#__codelineno-4-10"></a>units-rep-type ::= one of "aAbBdeEfFgGoxX"
|
||
</span><span id="__span-4-11"><a id="__codelineno-4-11" name="__codelineno-4-11" href="#__codelineno-4-11"></a>units-unit-modifier ::= [units-text-encoding, units-unit-symbol-denominator, units-unit-symbol-separator]
|
||
</span><span id="__span-4-12"><a id="__codelineno-4-12" name="__codelineno-4-12" href="#__codelineno-4-12"></a>units-text-encoding ::= one of "UA"
|
||
</span><span id="__span-4-13"><a id="__codelineno-4-13" name="__codelineno-4-13" href="#__codelineno-4-13"></a>units-unit-symbol-solidus ::= one of "oan"
|
||
</span><span id="__span-4-14"><a id="__codelineno-4-14" name="__codelineno-4-14" href="#__codelineno-4-14"></a>units-unit-symbol-separator ::= one of "sd"
|
||
</span></code></pre></div>
|
||
<p>In the above grammar:</p>
|
||
<ul>
|
||
<li><code>fill-and-align</code>, <code>width</code>, <code>sign</code>, <code>#</code>, <code>precision</code>, and <code>L</code> tokens, as well as the individual
|
||
tokens of <code>units-rep-type</code> are defined in the <a href="https://wg21.link/format.string.std">format.string.std</a>
|
||
chapter of the C++ standard specification,</li>
|
||
<li>tokens <code>Q</code> and <code>q</code> of <code>units-type</code> are described in the <a href="https://wg21.link/time.format">time.format</a>
|
||
chapter of the C++ standard specification,</li>
|
||
<li><code>units-text-encoding</code> tokens specify the unit text encoding:<ul>
|
||
<li><code>U</code> (default) uses the <strong>Unicode</strong> symbols defined by the <a href="../../../appendix/glossary/#si">SI</a>
|
||
specification (i.e. <code>m³</code>, <code>µs</code>)</li>
|
||
<li><code>A</code> token forces non-standard <strong>ASCII</strong>-only output (i.e. <code>m^3</code>, <code>us</code>)</li>
|
||
</ul>
|
||
</li>
|
||
<li><code>units-unit-symbol-solidus</code> tokens specify how the division of units should look like:<ul>
|
||
<li><code>o</code> (default) outputs <code>/</code> only when there is only <strong>one</strong> unit in the denominator, otherwise negative
|
||
exponents are printed (i.e. <code>m/s</code>, <code>kg m⁻¹ s⁻¹</code>)</li>
|
||
<li><code>a</code> <strong>always</strong> uses solidus (i.e. <code>m/s</code>, <code>kg/(m s)</code>)</li>
|
||
<li><code>n</code> <strong>never</strong> prints solidus, which means that negative exponents are always used (i.e. <code>m s⁻¹</code>,
|
||
<code>kg m⁻¹ s⁻¹</code>)</li>
|
||
</ul>
|
||
</li>
|
||
<li><code>units-unit-symbol-separator</code> tokens specify how multiplied unit symbols should be separated:<ul>
|
||
<li><code>s</code> (default) uses <strong>space</strong> as a separator (i.e. <code>kg m²/s²</code>)</li>
|
||
<li><code>d</code> uses half-high <strong>dot</strong> (<code>⋅</code>) as a separator (i.e. <code>kg⋅m²/s²</code>)</li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
<h3 id="default-formatting">Default formatting<a class="headerlink" href="#default-formatting" title="Permanent link">¶</a></h3>
|
||
<p>To format <code>quantity</code> values the formatting facility uses <code>units-format-spec</code>. If it is left empty,
|
||
the default formatting of <code>{:%Q %q}</code> is applied. The same default formatting is also applied
|
||
to the output streams. This is why the following code lines produce the same output:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-5-1"><a id="__codelineno-5-1" name="__codelineno-5-1" href="#__codelineno-5-1"></a><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Distance: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">km</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span>
|
||
</span><span id="__span-5-2"><a id="__codelineno-5-2" name="__codelineno-5-2" href="#__codelineno-5-2"></a><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">format</span><span class="p">(</span><span class="s">"Distance: {}</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">km</span><span class="p">);</span>
|
||
</span><span id="__span-5-3"><a id="__codelineno-5-3" name="__codelineno-5-3" href="#__codelineno-5-3"></a><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">format</span><span class="p">(</span><span class="s">"Distance: {:%Q %q}</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">km</span><span class="p">);</span>
|
||
</span></code></pre></div>
|
||
<h3 id="controlling-width-fill-and-alignment">Controlling width, fill, and alignment<a class="headerlink" href="#controlling-width-fill-and-alignment" title="Permanent link">¶</a></h3>
|
||
<p>To control width, fill, and alignment, the C++ standard grammar tokens <code>fill-and-align</code> and <code>width</code>
|
||
are being used, and they treat a quantity value and symbol as a contiguous text:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-6-1"><a id="__codelineno-6-1" name="__codelineno-6-1" href="#__codelineno-6-1"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"|{:0}|"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// |123 m|</span>
|
||
</span><span id="__span-6-2"><a id="__codelineno-6-2" name="__codelineno-6-2" href="#__codelineno-6-2"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"|{:10}|"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// | 123 m|</span>
|
||
</span><span id="__span-6-3"><a id="__codelineno-6-3" name="__codelineno-6-3" href="#__codelineno-6-3"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"|{:<10}|"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// |123 m |</span>
|
||
</span><span id="__span-6-4"><a id="__codelineno-6-4" name="__codelineno-6-4" href="#__codelineno-6-4"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"|{:>10}|"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// | 123 m|</span>
|
||
</span><span id="__span-6-5"><a id="__codelineno-6-5" name="__codelineno-6-5" href="#__codelineno-6-5"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"|{:^10}|"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// | 123 m |</span>
|
||
</span><span id="__span-6-6"><a id="__codelineno-6-6" name="__codelineno-6-6" href="#__codelineno-6-6"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"|{:*<10}|"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// |123 m*****|</span>
|
||
</span><span id="__span-6-7"><a id="__codelineno-6-7" name="__codelineno-6-7" href="#__codelineno-6-7"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"|{:*>10}|"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// |*****123 m|</span>
|
||
</span><span id="__span-6-8"><a id="__codelineno-6-8" name="__codelineno-6-8" href="#__codelineno-6-8"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"|{:*^10}|"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// |**123 m***|</span>
|
||
</span></code></pre></div>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">Note</p>
|
||
<p><a href="https://en.cppreference.com/w/cpp/io/print"><code>std::println</code> is a C++23 facility</a>. In case you
|
||
do not have access to C++23, you can obtain the same output with:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-7-1"><a id="__codelineno-7-1" name="__codelineno-7-1" href="#__codelineno-7-1"></a><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">format</span><span class="p">(</span><span class="s">"<format-string></span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="o"><</span><span class="n">format</span><span class="o">-</span><span class="n">args</span><span class="o">></span><span class="p">);</span>
|
||
</span></code></pre></div>
|
||
</div>
|
||
<h3 id="quantity-value-symbol-or-both">Quantity value, symbol, or both?<a class="headerlink" href="#quantity-value-symbol-or-both" title="Permanent link">¶</a></h3>
|
||
<p>The user can easily decide to either print a whole quantity (value and symbol) or only its parts.
|
||
Also, a custom style of quantity formatting might be applied:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-8-1"><a id="__codelineno-8-1" name="__codelineno-8-1" href="#__codelineno-8-1"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">km</span><span class="p">);</span><span class="w"> </span><span class="c1">// 123</span>
|
||
</span><span id="__span-8-2"><a id="__codelineno-8-2" name="__codelineno-8-2" href="#__codelineno-8-2"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">km</span><span class="p">);</span><span class="w"> </span><span class="c1">// km</span>
|
||
</span><span id="__span-8-3"><a id="__codelineno-8-3" name="__codelineno-8-3" href="#__codelineno-8-3"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q%q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">km</span><span class="p">);</span><span class="w"> </span><span class="c1">// 123km</span>
|
||
</span></code></pre></div>
|
||
<h3 id="quantity-value-formatting">Quantity value formatting<a class="headerlink" href="#quantity-value-formatting" title="Permanent link">¶</a></h3>
|
||
<p><code>sign</code> token allows us to specify how the value's sign is being printed:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-9-1"><a id="__codelineno-9-1" name="__codelineno-9-1" href="#__codelineno-9-1"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{0:%Q %q},{0:%+Q %q},{0:%-Q %q},{0:% Q %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1 m,+1 m,1 m, 1 m</span>
|
||
</span><span id="__span-9-2"><a id="__codelineno-9-2" name="__codelineno-9-2" href="#__codelineno-9-2"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{0:%Q %q},{0:%+Q %q},{0:%-Q %q},{0:% Q %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">-1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// -1 m,-1 m,-1 m,-1 m</span>
|
||
</span></code></pre></div>
|
||
<p>where:</p>
|
||
<ul>
|
||
<li><code>+</code> indicates that a sign should be used for both non-negative and negative numbers,</li>
|
||
<li><code>-</code> indicates that a sign should be used for negative numbers and negative zero only
|
||
(this is the default behavior),</li>
|
||
<li><code><space></code> indicates that a leading space should be used for non-negative numbers other
|
||
than negative zero, and a minus sign for negative numbers and negative zero.</li>
|
||
</ul>
|
||
<p><code>precision</code> token is allowed only for floating-point representation types:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-10-1"><a id="__codelineno-10-1" name="__codelineno-10-1" href="#__codelineno-10-1"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%.0Q %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1 m</span>
|
||
</span><span id="__span-10-2"><a id="__codelineno-10-2" name="__codelineno-10-2" href="#__codelineno-10-2"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%.1Q %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.2 m</span>
|
||
</span><span id="__span-10-3"><a id="__codelineno-10-3" name="__codelineno-10-3" href="#__codelineno-10-3"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%.2Q %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.23 m</span>
|
||
</span></code></pre></div>
|
||
<p><code>units-rep-type</code> specifies how a value of the representation type is being printed.
|
||
For integral types:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-11-1"><a id="__codelineno-11-1" name="__codelineno-11-1" href="#__codelineno-11-1"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%bQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 101010 m</span>
|
||
</span><span id="__span-11-2"><a id="__codelineno-11-2" name="__codelineno-11-2" href="#__codelineno-11-2"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%BQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 101010 m</span>
|
||
</span><span id="__span-11-3"><a id="__codelineno-11-3" name="__codelineno-11-3" href="#__codelineno-11-3"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%dQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 42 m</span>
|
||
</span><span id="__span-11-4"><a id="__codelineno-11-4" name="__codelineno-11-4" href="#__codelineno-11-4"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%oQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 52 m</span>
|
||
</span><span id="__span-11-5"><a id="__codelineno-11-5" name="__codelineno-11-5" href="#__codelineno-11-5"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%xQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 2a m</span>
|
||
</span><span id="__span-11-6"><a id="__codelineno-11-6" name="__codelineno-11-6" href="#__codelineno-11-6"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%XQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 2A m</span>
|
||
</span></code></pre></div>
|
||
<p>The above can be printed in an alternate version thanks to the <code>#</code> token:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-12-1"><a id="__codelineno-12-1" name="__codelineno-12-1" href="#__codelineno-12-1"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%#bQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 0b101010 m</span>
|
||
</span><span id="__span-12-2"><a id="__codelineno-12-2" name="__codelineno-12-2" href="#__codelineno-12-2"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%#BQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 0B101010 m</span>
|
||
</span><span id="__span-12-3"><a id="__codelineno-12-3" name="__codelineno-12-3" href="#__codelineno-12-3"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%#oQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 052 m</span>
|
||
</span><span id="__span-12-4"><a id="__codelineno-12-4" name="__codelineno-12-4" href="#__codelineno-12-4"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%#xQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 0x2a m</span>
|
||
</span><span id="__span-12-5"><a id="__codelineno-12-5" name="__codelineno-12-5" href="#__codelineno-12-5"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%#XQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 0X2A m</span>
|
||
</span></code></pre></div>
|
||
<p>For floating-point values, the <code>units-rep-type</code> token works as follows:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-13-1"><a id="__codelineno-13-1" name="__codelineno-13-1" href="#__codelineno-13-1"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%aQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 0x1.3c0ca2a5b1d5dp+0 m</span>
|
||
</span><span id="__span-13-2"><a id="__codelineno-13-2" name="__codelineno-13-2" href="#__codelineno-13-2"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%.3aQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 0x1.3c1p+0 m</span>
|
||
</span><span id="__span-13-3"><a id="__codelineno-13-3" name="__codelineno-13-3" href="#__codelineno-13-3"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%AQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 0X1.3C0CA2A5B1D5DP+0 m</span>
|
||
</span><span id="__span-13-4"><a id="__codelineno-13-4" name="__codelineno-13-4" href="#__codelineno-13-4"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%.3AQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 0X1.3C1P+0 m</span>
|
||
</span><span id="__span-13-5"><a id="__codelineno-13-5" name="__codelineno-13-5" href="#__codelineno-13-5"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%eQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.234568e+00 m</span>
|
||
</span><span id="__span-13-6"><a id="__codelineno-13-6" name="__codelineno-13-6" href="#__codelineno-13-6"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%.3eQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.235e+00 m</span>
|
||
</span><span id="__span-13-7"><a id="__codelineno-13-7" name="__codelineno-13-7" href="#__codelineno-13-7"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%EQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.234568E+00 m</span>
|
||
</span><span id="__span-13-8"><a id="__codelineno-13-8" name="__codelineno-13-8" href="#__codelineno-13-8"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%.3EQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.235E+00 m</span>
|
||
</span><span id="__span-13-9"><a id="__codelineno-13-9" name="__codelineno-13-9" href="#__codelineno-13-9"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%gQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.23457 m</span>
|
||
</span><span id="__span-13-10"><a id="__codelineno-13-10" name="__codelineno-13-10" href="#__codelineno-13-10"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%gQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678e8</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.23457e+08 m</span>
|
||
</span><span id="__span-13-11"><a id="__codelineno-13-11" name="__codelineno-13-11" href="#__codelineno-13-11"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%.3gQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.23 m</span>
|
||
</span><span id="__span-13-12"><a id="__codelineno-13-12" name="__codelineno-13-12" href="#__codelineno-13-12"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%.3gQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678e8</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.23e+08 m</span>
|
||
</span><span id="__span-13-13"><a id="__codelineno-13-13" name="__codelineno-13-13" href="#__codelineno-13-13"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%GQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.23457 m</span>
|
||
</span><span id="__span-13-14"><a id="__codelineno-13-14" name="__codelineno-13-14" href="#__codelineno-13-14"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%GQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678e8</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.23457E+08 m</span>
|
||
</span><span id="__span-13-15"><a id="__codelineno-13-15" name="__codelineno-13-15" href="#__codelineno-13-15"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%.3GQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.23 m</span>
|
||
</span><span id="__span-13-16"><a id="__codelineno-13-16" name="__codelineno-13-16" href="#__codelineno-13-16"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%.3GQ %q}"</span><span class="p">,</span><span class="w"> </span><span class="mf">1.2345678e8</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m</span><span class="p">);</span><span class="w"> </span><span class="c1">// 1.23E+08 m</span>
|
||
</span></code></pre></div>
|
||
<h3 id="unit-symbol-formatting">Unit symbol formatting<a class="headerlink" href="#unit-symbol-formatting" title="Permanent link">¶</a></h3>
|
||
<p>Unit symbols of some quantities are specified to use Unicode signs by the
|
||
<a href="../../../appendix/glossary/#si">SI</a> (i.e. <code>Ω</code> symbol for the resistance quantity). The <strong>mp-units</strong>
|
||
library follows this by default. From the engineering point of view, sometimes Unicode text might
|
||
not be the best solution as terminals of many (especially embedded) devices are ASCII-only.
|
||
In such a case, the unit symbol can be forced to be printed using ASCII-only characters thanks to
|
||
<code>units-text-encoding</code> token:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-14-1"><a id="__codelineno-14-1" name="__codelineno-14-1" href="#__codelineno-14-1"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{}"</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">si</span><span class="o">::</span><span class="n">ohm</span><span class="p">);</span><span class="w"> </span><span class="c1">// 10 Ω</span>
|
||
</span><span id="__span-14-2"><a id="__codelineno-14-2" name="__codelineno-14-2" href="#__codelineno-14-2"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q %Aq}"</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">si</span><span class="o">::</span><span class="n">ohm</span><span class="p">);</span><span class="w"> </span><span class="c1">// 10 ohm</span>
|
||
</span><span id="__span-14-3"><a id="__codelineno-14-3" name="__codelineno-14-3" href="#__codelineno-14-3"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{}"</span><span class="p">,</span><span class="w"> </span><span class="mi">125</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">us</span><span class="p">);</span><span class="w"> </span><span class="c1">// 125 µs</span>
|
||
</span><span id="__span-14-4"><a id="__codelineno-14-4" name="__codelineno-14-4" href="#__codelineno-14-4"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q %Aq}"</span><span class="p">,</span><span class="w"> </span><span class="mi">125</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">us</span><span class="p">);</span><span class="w"> </span><span class="c1">// 125 us</span>
|
||
</span><span id="__span-14-5"><a id="__codelineno-14-5" name="__codelineno-14-5" href="#__codelineno-14-5"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{}"</span><span class="p">,</span><span class="w"> </span><span class="mf">9.8</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p">(</span><span class="n">m</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">s2</span><span class="p">));</span><span class="w"> </span><span class="c1">// 9.8 m/s²</span>
|
||
</span><span id="__span-14-6"><a id="__codelineno-14-6" name="__codelineno-14-6" href="#__codelineno-14-6"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q %Aq}"</span><span class="p">,</span><span class="w"> </span><span class="mf">9.8</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p">(</span><span class="n">m</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">s2</span><span class="p">));</span><span class="w"> </span><span class="c1">// 9.8 m/s^2</span>
|
||
</span></code></pre></div>
|
||
<p>Additionally, both <a href="../../../appendix/glossary/#isq">ISQ</a> and <a href="../../../appendix/glossary/#si">SI</a>
|
||
leave some freedom on how to print unit symbols. This is why two additional tokens were introduced.</p>
|
||
<p><code>units-unit-symbol-solidus</code> specifies how the division of units should look like. By default,
|
||
<code>/</code> will be used only when the denominator contains only one unit. However, with the <code>a</code> or <code>n</code>
|
||
options, we can force the facility to print the <code>/</code> character always (even when there are more units
|
||
in the denominator), or never in which case a parenthesis will be added to enclose all denominator
|
||
units.</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-15-1"><a id="__codelineno-15-1" name="__codelineno-15-1" href="#__codelineno-15-1"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p">(</span><span class="n">m</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">s</span><span class="p">));</span><span class="w"> </span><span class="c1">// 1 m/s</span>
|
||
</span><span id="__span-15-2"><a id="__codelineno-15-2" name="__codelineno-15-2" href="#__codelineno-15-2"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p">(</span><span class="n">kg</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">s2</span><span class="p">));</span><span class="w"> </span><span class="c1">// 1 kg m⁻¹ s⁻²</span>
|
||
</span><span id="__span-15-3"><a id="__codelineno-15-3" name="__codelineno-15-3" href="#__codelineno-15-3"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q %aq}"</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p">(</span><span class="n">m</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">s</span><span class="p">));</span><span class="w"> </span><span class="c1">// 1 m/s</span>
|
||
</span><span id="__span-15-4"><a id="__codelineno-15-4" name="__codelineno-15-4" href="#__codelineno-15-4"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q %aq}"</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p">(</span><span class="n">kg</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">s2</span><span class="p">));</span><span class="w"> </span><span class="c1">// 1 kg/(m s²)</span>
|
||
</span><span id="__span-15-5"><a id="__codelineno-15-5" name="__codelineno-15-5" href="#__codelineno-15-5"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q %nq}"</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p">(</span><span class="n">m</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">s</span><span class="p">));</span><span class="w"> </span><span class="c1">// 1 m s⁻¹</span>
|
||
</span><span id="__span-15-6"><a id="__codelineno-15-6" name="__codelineno-15-6" href="#__codelineno-15-6"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q %nq}"</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p">(</span><span class="n">kg</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">s2</span><span class="p">));</span><span class="w"> </span><span class="c1">// 1 kg m⁻¹ s⁻²</span>
|
||
</span></code></pre></div>
|
||
<p>Also, there are a few options to separate the units being multiplied:</p>
|
||
<div class="admonition quote">
|
||
<p class="admonition-title">ISO 80000-1</p>
|
||
<p>When symbols for quantities are combined in a product of two or more quantities, this combination
|
||
is indicated in one of the following ways: <code>ab</code>, <code>a b</code>, <code>a · b</code>, <code>a × b</code></p>
|
||
<p><em>NOTE 1</em> In some fields, e.g., vector algebra, distinction is made between <code>a ∙ b</code> and <code>a × b</code>.</p>
|
||
</div>
|
||
<p>As of today, the <strong>mp-units</strong> library provides the support for <code>a b</code> and <code>a · b</code> only. Additionally,
|
||
we decided that the extraneous space in the latter case makes the result too verbose, so we decided
|
||
to just use the <code>·</code> symbol as a separator.</p>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">Note</p>
|
||
<p>Please let us know in case you require more formatting options here.</p>
|
||
</div>
|
||
<p>The <code>units-unit-symbol-separator</code> token allows us to obtain the following outputs:</p>
|
||
<div class="language-cpp highlight"><pre><span></span><code><span id="__span-16-1"><a id="__codelineno-16-1" name="__codelineno-16-1" href="#__codelineno-16-1"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q %q}"</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p">(</span><span class="n">kg</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m2</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">s2</span><span class="p">));</span><span class="w"> </span><span class="c1">// 1 kg m²/s²</span>
|
||
</span><span id="__span-16-2"><a id="__codelineno-16-2" name="__codelineno-16-2" href="#__codelineno-16-2"></a><span class="n">std</span><span class="o">::</span><span class="n">println</span><span class="p">(</span><span class="s">"{:%Q %dq}"</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p">(</span><span class="n">kg</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">m2</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">s2</span><span class="p">));</span><span class="w"> </span><span class="c1">// 1 kg⋅m²/s²</span>
|
||
</span></code></pre></div>
|
||
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