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< h1 id = "quick-start" > Quick Start< a class = "headerlink" href = "#quick-start" title = "Permanent link" > ¶ </ a ></ h1 >
< p > This chapter provides a quick introduction to get you started with < strong > mp-units</ strong > .
Much more details can be found in our < a href = "../../users_guide/terms_and_definitions/" > User's Guide</ a > .</ p >
< h2 id = "quantities" > Quantities< a class = "headerlink" href = "#quantities" title = "Permanent link" > ¶ </ a ></ h2 >
< p > A < strong > quantity</ strong > is a concrete amount of a unit representing a quantity type of a specified dimension with a
specific representation. It is represented in the library with a < code > quantity</ code > class template.</ p >
< p > The < a href = "../../appendix/references/#SIBrochure" > SI Brochure</ a > says:</ p >
< div class = "admonition quote" >
< p class = "admonition-title" > SI Brochure</ p >
< p > The value of the quantity is the product of the number and the unit. The space between the number
and the unit is regarded as a multiplication sign (just as a space between units implies
multiplication).</ p >
</ div >
< p > Following the above, the value of a quantity in the < strong > mp-units</ strong > library is created by multiplying
a number with a predefined unit:</ p >
< div class = "tabbed-set tabbed-alternate" data-tabs = "1:2" >< input checked = "checked" id = "__tabbed_1_1" name = "__tabbed_1" type = "radio" />< input id = "__tabbed_1_2" name = "__tabbed_1" type = "radio" />< div class = "tabbed-labels" >< label for = "__tabbed_1_1" > C++ modules</ label >< label for = "__tabbed_1_2" > Header files</ label ></ div >
< div class = "tabbed-content" >
< div class = "tabbed-block" >
< 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" > import</ span >< span class = "w" > </ span >< span class = "n" > mp_units</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-0-2" >< a id = "__codelineno-0-2" name = "__codelineno-0-2" href = "#__codelineno-0-2" ></ a >
</ span >< span id = "__span-0-3" >< a id = "__codelineno-0-3" name = "__codelineno-0-3" href = "#__codelineno-0-3" ></ 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 = "p" > ;</ span >
</ span >< span id = "__span-0-4" >< a id = "__codelineno-0-4" name = "__codelineno-0-4" href = "#__codelineno-0-4" ></ a >
</ span >< span id = "__span-0-5" >< a id = "__codelineno-0-5" name = "__codelineno-0-5" href = "#__codelineno-0-5" ></ a >< span class = "n" > quantity</ span >< span class = "w" > </ span >< span class = "n" > q</ span >< span class = "w" > </ span >< span class = "o" > =</ 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" > si</ span >< span class = "o" > ::</ span >< span class = "n" > metre</ 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" > second</ span >< span class = "p" > ;</ span >
</ span ></ code ></ pre ></ div >
</ div >
< div class = "tabbed-block" >
< 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 = "cp" > #include</ span >< span class = "w" > </ span >< span class = "cpf" > < mp-units/systems/si.h> </ span >
</ span >< span id = "__span-1-2" >< a id = "__codelineno-1-2" name = "__codelineno-1-2" href = "#__codelineno-1-2" ></ a >
</ 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 = "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 = "n" > quantity</ span >< span class = "w" > </ span >< span class = "n" > q</ span >< span class = "w" > </ span >< span class = "o" > =</ 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" > si</ span >< span class = "o" > ::</ span >< span class = "n" > metre</ 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" > second</ span >< span class = "p" > ;</ span >
</ span ></ code ></ pre ></ div >
</ div >
</ div >
</ div >
< div class = "admonition info" >
< p class = "admonition-title" > Info</ p >
< p > In case someone doesn't like the multiply syntax or there is an ambiguity between < code > operator*</ code >
provided by this and other libraries, there are two other ways to create a quantity:</ p >
< ol >
< li >
< p >< code > delta</ code > construction helper:</ p >
< div class = "tabbed-set tabbed-alternate" data-tabs = "2:2" >< input checked = "checked" id = "__tabbed_2_1" name = "__tabbed_2" type = "radio" />< input id = "__tabbed_2_2" name = "__tabbed_2" type = "radio" />< div class = "tabbed-labels" >< label for = "__tabbed_2_1" > C++ modules</ label >< label for = "__tabbed_2_2" > Header files</ label ></ div >
< div class = "tabbed-content" >
< div class = "tabbed-block" >
< 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 = "k" > import</ span >< span class = "w" > </ span >< span class = "n" > mp_units</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-2-2" >< a id = "__codelineno-2-2" name = "__codelineno-2-2" href = "#__codelineno-2-2" ></ a >
</ span >< span id = "__span-2-3" >< a id = "__codelineno-2-3" name = "__codelineno-2-3" href = "#__codelineno-2-3" ></ 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 = "p" > ;</ span >
</ span >< span id = "__span-2-4" >< a id = "__codelineno-2-4" name = "__codelineno-2-4" href = "#__codelineno-2-4" ></ a >
</ span >< span id = "__span-2-5" >< a id = "__codelineno-2-5" name = "__codelineno-2-5" href = "#__codelineno-2-5" ></ a >< span class = "n" > quantity</ span >< span class = "w" > </ span >< span class = "n" > q</ span >< span class = "w" > </ span >< span class = "o" > =</ span >< span class = "w" > </ span >< span class = "n" > delta</ span >< span class = "o" > < </ span >< span class = "n" > si</ span >< span class = "o" > ::</ span >< span class = "n" > metre</ 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" > second</ span >< span class = "o" > > </ span >< span class = "p" > (</ span >< span class = "mi" > 42</ span >< span class = "p" > );</ span >
</ span ></ code ></ pre ></ div >
</ div >
< div class = "tabbed-block" >
< 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 = "cp" > #include</ span >< span class = "w" > </ span >< span class = "cpf" > < mp-units/systems/si.h> </ span >
</ span >< span id = "__span-3-2" >< a id = "__codelineno-3-2" name = "__codelineno-3-2" href = "#__codelineno-3-2" ></ a >
</ span >< span id = "__span-3-3" >< a id = "__codelineno-3-3" name = "__codelineno-3-3" href = "#__codelineno-3-3" ></ 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 = "p" > ;</ span >
</ span >< span id = "__span-3-4" >< a id = "__codelineno-3-4" name = "__codelineno-3-4" href = "#__codelineno-3-4" ></ a >
</ span >< span id = "__span-3-5" >< a id = "__codelineno-3-5" name = "__codelineno-3-5" href = "#__codelineno-3-5" ></ a >< span class = "n" > quantity</ span >< span class = "w" > </ span >< span class = "n" > q</ span >< span class = "w" > </ span >< span class = "o" > =</ span >< span class = "w" > </ span >< span class = "n" > delta</ span >< span class = "o" > < </ span >< span class = "n" > si</ span >< span class = "o" > ::</ span >< span class = "n" > metre</ 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" > second</ span >< span class = "o" > > </ span >< span class = "p" > (</ span >< span class = "mi" > 42</ span >< span class = "p" > );</ span >
</ span ></ code ></ pre ></ div >
</ div >
</ div >
</ div >
</ li >
< li >
< p > A two-parameter constructor:</ p >
< div class = "tabbed-set tabbed-alternate" data-tabs = "3:2" >< input checked = "checked" id = "__tabbed_3_1" name = "__tabbed_3" type = "radio" />< input id = "__tabbed_3_2" name = "__tabbed_3" type = "radio" />< div class = "tabbed-labels" >< label for = "__tabbed_3_1" > C++ modules</ label >< label for = "__tabbed_3_2" > Header files</ label ></ div >
< div class = "tabbed-content" >
< div class = "tabbed-block" >
< div class = "language-cpp highlight" >< pre >< span ></ span >< code >< span id = "__span-4-1" >< a id = "__codelineno-4-1" name = "__codelineno-4-1" href = "#__codelineno-4-1" ></ a >< span class = "k" > import</ span >< span class = "w" > </ span >< span class = "n" > mp_units</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-4-2" >< a id = "__codelineno-4-2" name = "__codelineno-4-2" href = "#__codelineno-4-2" ></ a >
</ span >< span id = "__span-4-3" >< a id = "__codelineno-4-3" name = "__codelineno-4-3" href = "#__codelineno-4-3" ></ 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 = "p" > ;</ span >
</ span >< span id = "__span-4-4" >< a id = "__codelineno-4-4" name = "__codelineno-4-4" href = "#__codelineno-4-4" ></ a >
</ span >< span id = "__span-4-5" >< a id = "__codelineno-4-5" name = "__codelineno-4-5" href = "#__codelineno-4-5" ></ a >< span class = "n" > quantity</ span >< span class = "w" > </ span >< span class = "n" > q</ span >< span class = "p" > {</ span >< span class = "mi" > 42</ span >< span class = "p" > ,</ span >< span class = "w" > </ span >< span class = "n" > si</ span >< span class = "o" > ::</ span >< span class = "n" > metre</ 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" > second</ span >< span class = "p" > };</ span >
</ span ></ code ></ pre ></ div >
</ div >
< div class = "tabbed-block" >
< 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 = "cp" > #include</ span >< span class = "w" > </ span >< span class = "cpf" > < mp-units/systems/si.h> </ span >
</ span >< span id = "__span-5-2" >< a id = "__codelineno-5-2" name = "__codelineno-5-2" href = "#__codelineno-5-2" ></ a >
</ span >< span id = "__span-5-3" >< a id = "__codelineno-5-3" name = "__codelineno-5-3" href = "#__codelineno-5-3" ></ 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 = "p" > ;</ span >
</ span >< span id = "__span-5-4" >< a id = "__codelineno-5-4" name = "__codelineno-5-4" href = "#__codelineno-5-4" ></ a >
</ span >< span id = "__span-5-5" >< a id = "__codelineno-5-5" name = "__codelineno-5-5" href = "#__codelineno-5-5" ></ a >< span class = "n" > quantity</ span >< span class = "w" > </ span >< span class = "n" > q</ span >< span class = "p" > {</ span >< span class = "mi" > 42</ span >< span class = "p" > ,</ span >< span class = "w" > </ span >< span class = "n" > si</ span >< span class = "o" > ::</ span >< span class = "n" > metre</ 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" > second</ span >< span class = "p" > };</ span >
</ span ></ code ></ pre ></ div >
</ div >
</ div >
</ div >
</ li >
</ ol >
</ div >
< p > The above creates an instance of < code > quantity< derived_unit< si::metre, per< si::second>> {}, int> </ code > .
The same can be obtained using optional unit symbols:</ p >
< div class = "tabbed-set tabbed-alternate" data-tabs = "4:2" >< input checked = "checked" id = "__tabbed_4_1" name = "__tabbed_4" type = "radio" />< input id = "__tabbed_4_2" name = "__tabbed_4" type = "radio" />< div class = "tabbed-labels" >< label for = "__tabbed_4_1" > C++ modules</ label >< label for = "__tabbed_4_2" > Header files</ label ></ div >
< div class = "tabbed-content" >
< div class = "tabbed-block" >
< 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 = "k" > import</ span >< span class = "w" > </ span >< span class = "n" > mp_units</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-6-2" >< a id = "__codelineno-6-2" name = "__codelineno-6-2" href = "#__codelineno-6-2" ></ a >
</ span >< span id = "__span-6-3" >< a id = "__codelineno-6-3" name = "__codelineno-6-3" href = "#__codelineno-6-3" ></ 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 = "p" > ;</ span >
</ span >< span id = "__span-6-4" >< a id = "__codelineno-6-4" name = "__codelineno-6-4" href = "#__codelineno-6-4" ></ 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-6-5" >< a id = "__codelineno-6-5" name = "__codelineno-6-5" href = "#__codelineno-6-5" ></ a >
</ span >< span id = "__span-6-6" >< a id = "__codelineno-6-6" name = "__codelineno-6-6" href = "#__codelineno-6-6" ></ a >< span class = "n" > quantity</ span >< span class = "w" > </ span >< span class = "n" > q</ span >< span class = "w" > </ span >< span class = "o" > =</ 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 = "w" > </ span >< span class = "o" > /</ span >< span class = "w" > </ span >< span class = "n" > s</ span >< span class = "p" > ;</ span >
</ span ></ code ></ pre ></ div >
</ div >
< div class = "tabbed-block" >
< 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 = "cp" > #include</ span >< span class = "w" > </ span >< span class = "cpf" > < mp-units/systems/si.h> </ span >
</ span >< span id = "__span-7-2" >< a id = "__codelineno-7-2" name = "__codelineno-7-2" href = "#__codelineno-7-2" ></ a >
</ span >< span id = "__span-7-3" >< a id = "__codelineno-7-3" name = "__codelineno-7-3" href = "#__codelineno-7-3" ></ 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 = "p" > ;</ span >
</ span >< span id = "__span-7-4" >< a id = "__codelineno-7-4" name = "__codelineno-7-4" href = "#__codelineno-7-4" ></ 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-7-5" >< a id = "__codelineno-7-5" name = "__codelineno-7-5" href = "#__codelineno-7-5" ></ a >
</ span >< span id = "__span-7-6" >< a id = "__codelineno-7-6" name = "__codelineno-7-6" href = "#__codelineno-7-6" ></ a >< span class = "n" > quantity</ span >< span class = "w" > </ span >< span class = "n" > q</ span >< span class = "w" > </ span >< span class = "o" > =</ 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 = "w" > </ span >< span class = "o" > /</ span >< span class = "w" > </ span >< span class = "n" > s</ span >< span class = "p" > ;</ span >
</ span ></ code ></ pre ></ div >
</ div >
</ div >
</ div >
< div class = "admonition important" >
< p class = "admonition-title" > Important</ p >
< p > Unit symbols introduce a lot of short identifiers into the current scope, which may cause
naming collisions with unrelated but already existing identifiers in the code base.
This is why unit symbols are opt-in and typically should be imported only in the context
where they are being used (e.g., function scope).</ p >
< p > A user has several options here to choose from depending on the required scenario and possible
naming conflicts:</ p >
< div class = "tabbed-set tabbed-alternate" data-tabs = "5:4" >< input checked = "checked" id = "__tabbed_5_1" name = "__tabbed_5" type = "radio" />< input id = "__tabbed_5_2" name = "__tabbed_5" type = "radio" />< input id = "__tabbed_5_3" name = "__tabbed_5" type = "radio" />< input id = "__tabbed_5_4" name = "__tabbed_5" type = "radio" />< div class = "tabbed-labels" >< label for = "__tabbed_5_1" > using-directive</ label >< label for = "__tabbed_5_2" > using-declaration</ label >< label for = "__tabbed_5_3" > custom short identifier</ label >< label for = "__tabbed_5_4" > unit names</ label ></ div >
< div class = "tabbed-content" >
< div class = "tabbed-block" >
< p > Explicitly "import" all of the symbols of a specific system of units from a dedicated
< code > unit_symbols</ code > namespace with a
< a href = "https://en.cppreference.com/w/cpp/language/namespace#Using-directives" > using-directive</ a > :</ 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 = "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-8-2" >< a id = "__codelineno-8-2" name = "__codelineno-8-2" href = "#__codelineno-8-2" ></ a >
</ span >< span id = "__span-8-3" >< a id = "__codelineno-8-3" name = "__codelineno-8-3" href = "#__codelineno-8-3" ></ a >< span class = "kt" > void</ span >< span class = "w" > </ span >< span class = "nf" > foo</ span >< span class = "p" > (</ span >< span class = "kt" > double</ span >< span class = "w" > </ span >< span class = "n" > speed_m_s</ span >< span class = "p" > )</ span >
</ span >< span id = "__span-8-4" >< a id = "__codelineno-8-4" name = "__codelineno-8-4" href = "#__codelineno-8-4" ></ a >< span class = "p" > {</ span >
</ span >< span id = "__span-8-5" >< a id = "__codelineno-8-5" name = "__codelineno-8-5" href = "#__codelineno-8-5" ></ a >< span class = "w" > </ span >< span class = "c1" > // imports all the SI symbols at once</ span >
</ span >< span id = "__span-8-6" >< a id = "__codelineno-8-6" name = "__codelineno-8-6" href = "#__codelineno-8-6" ></ a >< span class = "w" > </ span >< span class = "k" > using</ span >< span class = "w" > </ span >< span class = "k" > namespace</ span >< span class = "w" > </ span >< span class = "nn" > si</ span >< span class = "o" > ::</ span >< span class = "nn" > unit_symbols</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-8-7" >< a id = "__codelineno-8-7" name = "__codelineno-8-7" href = "#__codelineno-8-7" ></ a >< span class = "w" > </ span >< span class = "n" > quantity</ span >< span class = "w" > </ span >< span class = "n" > speed</ span >< span class = "w" > </ span >< span class = "o" > =</ span >< span class = "w" > </ span >< span class = "n" > speed_m_s</ 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" > s</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-8-8" >< a id = "__codelineno-8-8" name = "__codelineno-8-8" href = "#__codelineno-8-8" ></ a >< span class = "w" > </ span >< span class = "c1" > // ...</ span >
</ span >< span id = "__span-8-9" >< a id = "__codelineno-8-9" name = "__codelineno-8-9" href = "#__codelineno-8-9" ></ a >< span class = "p" > }</ span >
</ span ></ code ></ pre ></ div >
< div class = "admonition note" >
< p class = "admonition-title" > Note</ p >
< p > This solution is perfect for small and isolated scopes but can cause surprising issues
when used in larger scopes or when used for the entire program namespace.</ p >
< p > There are 29 named units in SI, and each of them has many prefixed variations (e.g.,
< code > ng</ code > , < code > kcd</ code > , ...). It is pretty easy to introduce a name collision with those.</ p >
</ div >
</ div >
< div class = "tabbed-block" >
< p > Selectively bring only the required and not-conflicting symbols with
< a href = "https://en.cppreference.com/w/cpp/language/using_declaration" > using-declarations</ a > :</ 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 = "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-9-2" >< a id = "__codelineno-9-2" name = "__codelineno-9-2" href = "#__codelineno-9-2" ></ a >
</ span >< span id = "__span-9-3" >< a id = "__codelineno-9-3" name = "__codelineno-9-3" href = "#__codelineno-9-3" ></ a >< span class = "kt" > void</ span >< span class = "w" > </ span >< span class = "nf" > foo</ span >< span class = "p" > (</ span >< span class = "kt" > double</ span >< span class = "w" > </ span >< span class = "n" > N</ span >< span class = "p" > )</ span >
</ span >< span id = "__span-9-4" >< a id = "__codelineno-9-4" name = "__codelineno-9-4" href = "#__codelineno-9-4" ></ a >< span class = "p" > {</ span >
</ span >< span id = "__span-9-5" >< a id = "__codelineno-9-5" name = "__codelineno-9-5" href = "#__codelineno-9-5" ></ a >< span class = "w" > </ span >< span class = "c1" > // ' N' function parameter would collide with the SI symbol for Newton, so we only bring what we need</ span >
</ span >< span id = "__span-9-6" >< a id = "__codelineno-9-6" name = "__codelineno-9-6" href = "#__codelineno-9-6" ></ a >< span class = "w" > </ span >< span class = "k" > using</ span >< span class = "w" > </ span >< span class = "n" > si</ span >< span class = "o" > ::</ span >< span class = "n" > unit_symbols</ span >< span class = "o" > ::</ span >< span class = "n" > m</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-9-7" >< a id = "__codelineno-9-7" name = "__codelineno-9-7" href = "#__codelineno-9-7" ></ a >< span class = "w" > </ span >< span class = "k" > using</ span >< span class = "w" > </ span >< span class = "n" > si</ span >< span class = "o" > ::</ span >< span class = "n" > unit_symbols</ span >< span class = "o" > ::</ span >< span class = "n" > s</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-9-8" >< a id = "__codelineno-9-8" name = "__codelineno-9-8" href = "#__codelineno-9-8" ></ a >< span class = "w" > </ span >< span class = "n" > quantity</ span >< span class = "w" > </ span >< span class = "n" > speed</ span >< span class = "w" > </ span >< span class = "o" > =</ span >< span class = "w" > </ span >< span class = "n" > N</ 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" > s</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-9-9" >< a id = "__codelineno-9-9" name = "__codelineno-9-9" href = "#__codelineno-9-9" ></ a >< span class = "w" > </ span >< span class = "c1" > // ...</ span >
</ span >< span id = "__span-9-10" >< a id = "__codelineno-9-10" name = "__codelineno-9-10" href = "#__codelineno-9-10" ></ a >< span class = "p" > }</ span >
</ span ></ code ></ pre ></ div >
</ div >
< div class = "tabbed-block" >
< p > Specify a custom not conflicting unit identifier for a unit:</ 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 = "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-10-2" >< a id = "__codelineno-10-2" name = "__codelineno-10-2" href = "#__codelineno-10-2" ></ a >
</ span >< span id = "__span-10-3" >< a id = "__codelineno-10-3" name = "__codelineno-10-3" href = "#__codelineno-10-3" ></ a >< span class = "kt" > void</ span >< span class = "w" > </ span >< span class = "nf" > foo</ span >< span class = "p" > (</ span >< span class = "kt" > double</ span >< span class = "w" > </ span >< span class = "n" > speed_m_s</ span >< span class = "p" > )</ span >
</ span >< span id = "__span-10-4" >< a id = "__codelineno-10-4" name = "__codelineno-10-4" href = "#__codelineno-10-4" ></ a >< span class = "p" > {</ span >
</ span >< span id = "__span-10-5" >< a id = "__codelineno-10-5" name = "__codelineno-10-5" href = "#__codelineno-10-5" ></ a >< span class = "w" > </ span >< span class = "c1" > // names of some local variables are conflicting with the symbols we want to use</ span >
</ span >< span id = "__span-10-6" >< a id = "__codelineno-10-6" name = "__codelineno-10-6" href = "#__codelineno-10-6" ></ a >< span class = "w" > </ span >< span class = "k" > auto</ span >< span class = "w" > </ span >< span class = "n" > m</ span >< span class = "w" > </ span >< span class = "o" > =</ span >< span class = "w" > </ span >< span class = "p" > ...;</ span >
</ span >< span id = "__span-10-7" >< a id = "__codelineno-10-7" name = "__codelineno-10-7" href = "#__codelineno-10-7" ></ a >< span class = "w" > </ span >< span class = "k" > auto</ span >< span class = "w" > </ span >< span class = "n" > s</ span >< span class = "w" > </ span >< span class = "o" > =</ span >< span class = "w" > </ span >< span class = "p" > ...;</ span >
</ span >< span id = "__span-10-8" >< a id = "__codelineno-10-8" name = "__codelineno-10-8" href = "#__codelineno-10-8" ></ a >
</ span >< span id = "__span-10-9" >< a id = "__codelineno-10-9" name = "__codelineno-10-9" href = "#__codelineno-10-9" ></ a >< span class = "w" > </ span >< span class = "k" > constexpr</ span >< span class = "w" > </ span >< span class = "n" > Unit</ span >< span class = "w" > </ span >< span class = "k" > auto</ span >< span class = "w" > </ span >< span class = "n" > mps</ 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" > metre</ 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" > second</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-10-10" >< a id = "__codelineno-10-10" name = "__codelineno-10-10" href = "#__codelineno-10-10" ></ a >< span class = "w" > </ span >< span class = "n" > quantity</ span >< span class = "w" > </ span >< span class = "n" > speed</ span >< span class = "w" > </ span >< span class = "o" > =</ span >< span class = "w" > </ span >< span class = "n" > speed_m_s</ span >< span class = "w" > </ span >< span class = "o" > *</ span >< span class = "w" > </ span >< span class = "n" > mps</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-10-11" >< a id = "__codelineno-10-11" name = "__codelineno-10-11" href = "#__codelineno-10-11" ></ a >< span class = "p" > }</ span >
</ span ></ code ></ pre ></ div >
</ div >
< div class = "tabbed-block" >
< p > Full unit names are straightforward to use and often provide the most readable code:</ 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 = "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-11-2" >< a id = "__codelineno-11-2" name = "__codelineno-11-2" href = "#__codelineno-11-2" ></ a >
</ span >< span id = "__span-11-3" >< a id = "__codelineno-11-3" name = "__codelineno-11-3" href = "#__codelineno-11-3" ></ a >< span class = "kt" > void</ span >< span class = "w" > </ span >< span class = "nf" > foo</ span >< span class = "p" > (</ span >< span class = "kt" > double</ span >< span class = "w" > </ span >< span class = "n" > m</ span >< span class = "p" > ,</ span >< span class = "w" > </ span >< span class = "kt" > double</ span >< span class = "w" > </ span >< span class = "n" > s</ span >< span class = "p" > )</ span >
</ span >< span id = "__span-11-4" >< a id = "__codelineno-11-4" name = "__codelineno-11-4" href = "#__codelineno-11-4" ></ a >< span class = "p" > {</ span >
</ span >< span id = "__span-11-5" >< a id = "__codelineno-11-5" name = "__codelineno-11-5" href = "#__codelineno-11-5" ></ a >< span class = "w" > </ span >< span class = "n" > quantity</ span >< span class = "w" > </ span >< span class = "n" > speed</ 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" > si</ span >< span class = "o" > ::</ span >< span class = "n" > metre</ span >< span class = "w" > </ span >< span class = "o" > /</ span >< span class = "w" > </ span >< span class = "p" > (</ span >< span class = "n" > s</ 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" > second</ span >< span class = "p" > );</ span >
</ span >< span id = "__span-11-6" >< a id = "__codelineno-11-6" name = "__codelineno-11-6" href = "#__codelineno-11-6" ></ a >< span class = "w" > </ span >< span class = "c1" > // ...</ span >
</ span >< span id = "__span-11-7" >< a id = "__codelineno-11-7" name = "__codelineno-11-7" href = "#__codelineno-11-7" ></ a >< span class = "p" > }</ span >
</ span ></ code ></ pre ></ div >
</ div >
</ div >
</ div >
</ div >
< p > Quantities of the same kind can be added, subtracted, and compared to each other:</ p >
< div class = "tabbed-set tabbed-alternate" data-tabs = "6:2" >< input checked = "checked" id = "__tabbed_6_1" name = "__tabbed_6" type = "radio" />< input id = "__tabbed_6_2" name = "__tabbed_6" type = "radio" />< div class = "tabbed-labels" >< label for = "__tabbed_6_1" > C++ modules</ label >< label for = "__tabbed_6_2" > Header files</ label ></ div >
< div class = "tabbed-content" >
< div class = "tabbed-block" >
< 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 = "k" > import</ span >< span class = "w" > </ span >< span class = "n" > mp_units</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-12-2" >< a id = "__codelineno-12-2" name = "__codelineno-12-2" href = "#__codelineno-12-2" ></ a >
</ span >< span id = "__span-12-3" >< a id = "__codelineno-12-3" name = "__codelineno-12-3" href = "#__codelineno-12-3" ></ 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 = "p" > ;</ span >
</ span >< span id = "__span-12-4" >< a id = "__codelineno-12-4" name = "__codelineno-12-4" href = "#__codelineno-12-4" ></ 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-12-5" >< a id = "__codelineno-12-5" name = "__codelineno-12-5" href = "#__codelineno-12-5" ></ a >
</ span >< span id = "__span-12-6" >< a id = "__codelineno-12-6" name = "__codelineno-12-6" href = "#__codelineno-12-6" ></ a >< span class = "k" > static_assert</ span >< span class = "p" > (</ span >< span class = "mi" > 1</ 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 = "mi" > 50</ 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 = "mi" > 1050</ span >< span class = "w" > </ span >< span class = "o" > *</ span >< span class = "w" > </ span >< span class = "n" > m</ span >< span class = "p" > );</ span >
</ span ></ code ></ pre ></ div >
</ div >
< div class = "tabbed-block" >
< 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 = "cp" > #include</ span >< span class = "w" > </ span >< span class = "cpf" > < mp-units/systems/si.h> </ span >
</ span >< span id = "__span-13-2" >< a id = "__codelineno-13-2" name = "__codelineno-13-2" href = "#__codelineno-13-2" ></ a >
</ span >< span id = "__span-13-3" >< a id = "__codelineno-13-3" name = "__codelineno-13-3" href = "#__codelineno-13-3" ></ 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 = "p" > ;</ span >
</ span >< span id = "__span-13-4" >< a id = "__codelineno-13-4" name = "__codelineno-13-4" href = "#__codelineno-13-4" ></ 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-13-5" >< a id = "__codelineno-13-5" name = "__codelineno-13-5" href = "#__codelineno-13-5" ></ a >
</ span >< span id = "__span-13-6" >< a id = "__codelineno-13-6" name = "__codelineno-13-6" href = "#__codelineno-13-6" ></ a >< span class = "k" > static_assert</ span >< span class = "p" > (</ span >< span class = "mi" > 1</ 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 = "mi" > 50</ 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 = "mi" > 1050</ span >< span class = "w" > </ span >< span class = "o" > *</ span >< span class = "w" > </ span >< span class = "n" > m</ span >< span class = "p" > );</ span >
</ span ></ code ></ pre ></ div >
</ div >
</ div >
</ div >
< p > Various quantities can be multiplied or divided by each other:</ 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 = "k" > static_assert</ span >< span class = "p" > (</ span >< span class = "mi" > 140</ 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 = "p" > (</ 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 class = "w" > </ span >< span class = "o" > ==</ span >< span class = "w" > </ span >< span class = "mi" > 70</ 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 = "n" > h</ span >< span class = "p" > );</ span >
</ span ></ code ></ pre ></ div >
< div class = "admonition note" >
< p class = "admonition-title" > Note</ p >
< p > In case you wonder why this library does not use UDLs to create quantities, please check
our < a href = "../faq/#why-dont-we-use-udls-to-create-quantities" > FAQ</ a > .</ p >
</ div >
< h2 id = "quantity-points" > Quantity points< a class = "headerlink" href = "#quantity-points" title = "Permanent link" > ¶ </ a ></ h2 >
< p > The quantity point specifies an absolute quantity with respect to an origin.
If no origin is provided explicitly, an implicit one will be provided by the library.</ p >
< p > Together with quantities, they model < a href = "../../users_guide/framework_basics/the_affine_space/" > The Affine Space</ a > .</ p >
< p > Quantity points should be used in all places where adding two values is meaningless
(e.g., temperature points, timestamps, altitudes, readouts from the car's odometer, etc.).</ p >
< p > The set of operations that can be done on quantity points is limited compared to quantities.
This introduces an additional type-safety.</ p >
< div class = "tabbed-set tabbed-alternate" data-tabs = "7:2" >< input checked = "checked" id = "__tabbed_7_1" name = "__tabbed_7" type = "radio" />< input id = "__tabbed_7_2" name = "__tabbed_7" type = "radio" />< div class = "tabbed-labels" >< label for = "__tabbed_7_1" > C++ modules</ label >< label for = "__tabbed_7_2" > Header files</ label ></ div >
< div class = "tabbed-content" >
< div class = "tabbed-block" >
< 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 = "cp" > #include</ span >< span class = "w" > </ span >< span class = "cpf" > < print> </ span >
</ span >< span id = "__span-15-2" >< a id = "__codelineno-15-2" name = "__codelineno-15-2" href = "#__codelineno-15-2" ></ a >< span class = "k" > import</ span >< span class = "w" > </ span >< span class = "n" > mp_units</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-15-3" >< a id = "__codelineno-15-3" name = "__codelineno-15-3" href = "#__codelineno-15-3" ></ a >
</ span >< span id = "__span-15-4" >< a id = "__codelineno-15-4" name = "__codelineno-15-4" href = "#__codelineno-15-4" ></ a >< span class = "kt" > int</ span >< span class = "w" > </ span >< span class = "nf" > main</ span >< span class = "p" > ()</ span >
</ span >< span id = "__span-15-5" >< a id = "__codelineno-15-5" name = "__codelineno-15-5" href = "#__codelineno-15-5" ></ a >< span class = "p" > {</ span >
</ span >< span id = "__span-15-6" >< a id = "__codelineno-15-6" name = "__codelineno-15-6" href = "#__codelineno-15-6" ></ a >< span class = "w" > </ span >< 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-15-7" >< a id = "__codelineno-15-7" name = "__codelineno-15-7" href = "#__codelineno-15-7" ></ a >< span class = "w" > </ span >< 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-15-8" >< a id = "__codelineno-15-8" name = "__codelineno-15-8" href = "#__codelineno-15-8" ></ a >< span class = "w" > </ span >< 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" > usc</ span >< span class = "o" > ::</ span >< span class = "nn" > unit_symbols</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-15-9" >< a id = "__codelineno-15-9" name = "__codelineno-15-9" href = "#__codelineno-15-9" ></ a >
</ span >< span id = "__span-15-10" >< a id = "__codelineno-15-10" name = "__codelineno-15-10" href = "#__codelineno-15-10" ></ a >< span class = "w" > </ span >< span class = "n" > quantity_point</ span >< span class = "w" > </ span >< span class = "n" > temp</ span >< span class = "w" > </ span >< span class = "o" > =</ span >< span class = "w" > </ span >< span class = "n" > absolute</ span >< span class = "o" > < </ span >< span class = "n" > deg_C</ span >< span class = "o" > > </ span >< span class = "p" > (</ span >< span class = "mf" > 20.</ span >< span class = "p" > );</ span >
</ span >< span id = "__span-15-11" >< a id = "__codelineno-15-11" name = "__codelineno-15-11" href = "#__codelineno-15-11" ></ a >< span class = "w" > </ span >< span class = "n" > std</ span >< span class = "o" > ::</ span >< span class = "n" > println</ span >< span class = "p" > (</ span >< span class = "s" > " Temperature: {} ({})" </ span >< span class = "p" > ,</ span >
</ span >< span id = "__span-15-12" >< a id = "__codelineno-15-12" name = "__codelineno-15-12" href = "#__codelineno-15-12" ></ a >< span class = "w" > </ span >< span class = "n" > temp</ span >< span class = "p" > .</ span >< span class = "n" > quantity_from_zero</ span >< span class = "p" > (),</ span >
</ span >< span id = "__span-15-13" >< a id = "__codelineno-15-13" name = "__codelineno-15-13" href = "#__codelineno-15-13" ></ a >< span class = "w" > </ span >< span class = "n" > temp</ span >< span class = "p" > .</ span >< span class = "n" > in</ span >< span class = "p" > (</ span >< span class = "n" > deg_F</ span >< span class = "p" > ).</ span >< span class = "n" > quantity_from_zero</ span >< span class = "p" > ());</ span >
</ span >< span id = "__span-15-14" >< a id = "__codelineno-15-14" name = "__codelineno-15-14" href = "#__codelineno-15-14" ></ a >< span class = "p" > }</ span >
</ span ></ code ></ pre ></ div >
</ div >
< div class = "tabbed-block" >
< 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 = "cp" > #include</ span >< span class = "w" > </ span >< span class = "cpf" > < mp-units/format.h> </ span >
</ span >< span id = "__span-16-2" >< a id = "__codelineno-16-2" name = "__codelineno-16-2" href = "#__codelineno-16-2" ></ a >< span class = "cp" > #include</ span >< span class = "w" > </ span >< span class = "cpf" > < mp-units/systems/si.h> </ span >
</ span >< span id = "__span-16-3" >< a id = "__codelineno-16-3" name = "__codelineno-16-3" href = "#__codelineno-16-3" ></ a >< span class = "cp" > #include</ span >< span class = "w" > </ span >< span class = "cpf" > < mp-units/systems/usc.h> </ span >
</ span >< span id = "__span-16-4" >< a id = "__codelineno-16-4" name = "__codelineno-16-4" href = "#__codelineno-16-4" ></ a >< span class = "cp" > #include</ span >< span class = "w" > </ span >< span class = "cpf" > < print> </ span >
</ span >< span id = "__span-16-5" >< a id = "__codelineno-16-5" name = "__codelineno-16-5" href = "#__codelineno-16-5" ></ a >
</ span >< span id = "__span-16-6" >< a id = "__codelineno-16-6" name = "__codelineno-16-6" href = "#__codelineno-16-6" ></ a >< span class = "kt" > int</ span >< span class = "w" > </ span >< span class = "nf" > main</ span >< span class = "p" > ()</ span >
</ span >< span id = "__span-16-7" >< a id = "__codelineno-16-7" name = "__codelineno-16-7" href = "#__codelineno-16-7" ></ a >< span class = "p" > {</ span >
</ span >< span id = "__span-16-8" >< a id = "__codelineno-16-8" name = "__codelineno-16-8" href = "#__codelineno-16-8" ></ a >< span class = "w" > </ span >< 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-16-9" >< a id = "__codelineno-16-9" name = "__codelineno-16-9" href = "#__codelineno-16-9" ></ a >< span class = "w" > </ span >< 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-16-10" >< a id = "__codelineno-16-10" name = "__codelineno-16-10" href = "#__codelineno-16-10" ></ a >< span class = "w" > </ span >< 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" > usc</ span >< span class = "o" > ::</ span >< span class = "nn" > unit_symbols</ span >< span class = "p" > ;</ span >
</ span >< span id = "__span-16-11" >< a id = "__codelineno-16-11" name = "__codelineno-16-11" href = "#__codelineno-16-11" ></ a >
</ span >< span id = "__span-16-12" >< a id = "__codelineno-16-12" name = "__codelineno-16-12" href = "#__codelineno-16-12" ></ a >< span class = "w" > </ span >< span class = "n" > quantity_point</ span >< span class = "w" > </ span >< span class = "n" > temp</ span >< span class = "w" > </ span >< span class = "o" > =</ span >< span class = "w" > </ span >< span class = "n" > absolute</ span >< span class = "o" > < </ span >< span class = "n" > deg_C</ span >< span class = "o" > > </ span >< span class = "p" > (</ span >< span class = "mf" > 20.</ span >< span class = "p" > );</ span >
</ span >< span id = "__span-16-13" >< a id = "__codelineno-16-13" name = "__codelineno-16-13" href = "#__codelineno-16-13" ></ a >< span class = "w" > </ span >< span class = "n" > std</ span >< span class = "o" > ::</ span >< span class = "n" > println</ span >< span class = "p" > (</ span >< span class = "s" > " Temperature: {} ({})" </ span >< span class = "p" > ,</ span >
</ span >< span id = "__span-16-14" >< a id = "__codelineno-16-14" name = "__codelineno-16-14" href = "#__codelineno-16-14" ></ a >< span class = "w" > </ span >< span class = "n" > temp</ span >< span class = "p" > .</ span >< span class = "n" > quantity_from_zero</ span >< span class = "p" > (),</ span >
</ span >< span id = "__span-16-15" >< a id = "__codelineno-16-15" name = "__codelineno-16-15" href = "#__codelineno-16-15" ></ a >< span class = "w" > </ span >< span class = "n" > temp</ span >< span class = "p" > .</ span >< span class = "n" > in</ span >< span class = "p" > (</ span >< span class = "n" > deg_F</ span >< span class = "p" > ).</ span >< span class = "n" > quantity_from_zero</ span >< span class = "p" > ());</ span >
</ span >< span id = "__span-16-16" >< a id = "__codelineno-16-16" name = "__codelineno-16-16" href = "#__codelineno-16-16" ></ a >< span class = "p" > }</ span >
</ span ></ code ></ pre ></ div >
</ div >
</ div >
</ div >
< p > The above outputs:</ p >
< div class = "language-text highlight" >< pre >< span ></ span >< code >< span id = "__span-17-1" >< a id = "__codelineno-17-1" name = "__codelineno-17-1" href = "#__codelineno-17-1" ></ a > Temperature: 20 ℃ (68 ℉)
</ span ></ code ></ pre ></ div >
< div class = "admonition info" >
< p class = "admonition-title" > Info</ p >
< p > Check < a href = "../../users_guide/framework_basics/the_affine_space/" > The Affine Space</ a > chapter to learn
more about quantity points.</ p >
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