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FIx #5536

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[SVN r71901]
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Antony Polukhin
2011-05-12 17:21:07 +00:00
parent c28efea0b3
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1 changed files with 49 additions and 21 deletions
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lexical_cast.htm
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@ -196,38 +196,60 @@ public:
failure.
<hr>
<!--
The original design of lexical_cast library does not supports throwing/nonthrowing behaviour, default values,
locales... BOOST_LEXICAL_CAST_ASSUME_C_LOCALE is a good optimization, but it breaks down the original design.
-->
<!--
<h2><a name="BOOST_LEXICAL_CAST_ASSUME_C_LOCALE"><code>BOOST_LEXICAL_CAST_ASSUME_C_LOCALE</code></a></h2>
<blockquote><pre>#define BOOST_LEXICAL_CAST_ASSUME_C_LOCALE
<blockquote><pre>#define BOOST_LEXICAL_CAST_ASSUME_C_LOCALE</blockquote></pre>
or,
g++ -DBOOST_LEXICAL_CAST_ASSUME_C_LOCALE ... (gcc on Linux/Unix)
cl.exe /DBOOST_LEXICAL_CAST_ASSUME_C_LOCALE ... (Visual C++ on Windows)
<blockquote><pre>g++ -DBOOST_LEXICAL_CAST_ASSUME_C_LOCALE ... (gcc on Linux/Unix)</blockquote></pre>
<blockquote><pre>cl.exe /DBOOST_LEXICAL_CAST_ASSUME_C_LOCALE ... (Visual C++ on Windows)</blockquote></pre>
</pre>
Eliminate an overhead of <code>std::locale</code> if your program runs in the "C" locale. If the option is set but a program runs in other locale, <code>lexical_cast</code> result is unspecified.
<hr>
-->
<h2><a name="faq">Frequently Asked Questions</h2>
<p> Q: Why does <code>lexical_cast&lt;int8_t&gt;("127")</code> throw <code>bad_lexical_cast</code>?
<br> A: The type <code>int8_t</code> is a typedef to <code>char</code> or <code>signed char</code>.
<h2><a name="faq">Frequently Asked Questions</a></h2>
<table>
<tr>
<td valign="top"><b>Question:</b></td>
<td>Why does <code>lexical_cast&lt;int8_t&gt;("127")</code> throw <code>bad_lexical_cast</code>?</td>
</tr>
<tr>
<td valign="top"><b>Answer:</b></td>
<td>The type <code>int8_t</code> is a typedef to <code>char</code> or <code>signed char</code>.
Lexical conversion to these types is simply reading a byte from source but since the source has
more than one byte, the exception is thrown.
<p>Please use other integer types such as <code>int</code> or <code>short int</code>. If bounds checking
Please use other integer types such as <code>int</code> or <code>short int</code>. If bounds checking
is important, you can also call <a href="../../libs/numeric/conversion/doc/html/boost_numericconversion/improved_numeric_cast__.html">numeric_cast</a>:
<pre><a href="../../libs/numeric/conversion/doc/html/boost_numericconversion/improved_numeric_cast__.html">numeric_cast</a>&lt;int8_t&gt;(lexical_cast&lt;int&gt;("127"));</pre>
</td>
</tr>
<tr>
<td valign="top"><b>Question:</b></td><td>What does <code>lexical_cast&lt;std::string&gt;</code> of an <code>int8_t</code> or <code>uint8_t</code> not do what I expect?</td>
</tr>
<tr>
<td valign="top"><b>Answer:</b></td><td>As above, note that <code>int8_t</code> and <code>uint8_t</code> are actually chars and are formatted as such. To avoid this, cast to an integer type first:
<pre>lexical_cast&lt;std::string&gt;(static_cast&lt;int&gt;(n));</pre>
</td>
</tr>
<tr>
<td valign="top"><b>Question:</b></td>
<td>The implementation always resets the <code>ios_base::skipws</code> flag of an underlying stream object. It breaks my <code>operator&gt;&gt;</code> that works only in presence of this flag. Can you remove code that resets the flag?</td>
</tr>
<tr>
<td valign="top"><b>Answer:</b></td>
<td>May be in a future version. There is no requirement in <a href="#n1973">[N1973]</a> to reset the flag but remember that <a href="#n1973">[N1973]</a> is not yet accepted by the committee. By the way, it's a great opportunity to make your <code>operator&gt;&gt;</code> conform to the standard. Read a good C++ book, study <code>std::sentry</code> and <a href="../../libs/io/doc/ios_state.html">ios_state_saver</a>.
</td>
</tr>
</table>
<p> Q: What does <code>lexical_cast&lt;std::string&gt;</code> of an <code>int8_t</code> or <code>uint8_t</code> not do what I expect?
<br> A: As above, note that <code>int8_t</code> and <code>uint8_t</code> are actually chars and are formatted as such. To avoid this, cast to an integer type first:
<pre>lexical_cast&lt;std::string&gt;(static_cast&lt;int&gt;(n));</pre>
<p> Q: The implementation always resets the <code>ios_base::skipws</code> flag of an underlying stream object. It breaks my <code>operator&gt;&gt;</code> that works only in presence of this flag. Can you remove code that resets the flag?
<br> A: May be in a future version. There is no requirement in <a href="#n1973">[N1973]</a> to reset the flag but remember that <a href="#n1973">[N1973]</a> is not yet accepted by the committee. By the way, it's a great opportunity to make your <code>operator&gt;&gt;</code> conform to the standard. Read a good C++ book, study <code>std::sentry</code> and <a href="../../libs/io/doc/ios_state.html">ios_state_saver</a>.
</ul>
<h2><a name="references">References</h2>
<h2><a name="references">References</a></h2>
<ul type="square">
<a name="n1973"></a><li> [N1973] Kevlin Henney, Beman Dawes, Lexical Conversion Library Proposal for TR2,
<li><a name="n1973"></a>[N1973] Kevlin Henney, Beman Dawes, Lexical Conversion Library Proposal for TR2,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1973.html">N1973</a>.
<a name="tuning"></a><li> [Tuning] Alexander Nasonov, Fine Tuning for lexical_cast,
<a href="http://accu.org/index.php/journals/1375">Overload #74</a> (<a href="http://www.accu.org/var/uploads/journals/overload74.pdf">PDF</a>),
@ -276,6 +298,12 @@ Eliminate an overhead of <code>std::locale</code> if your program runs in the "C
<p>
<hr>
<div align="right"><small><i>&copy; Copyright Kevlin Henney, 2000&#150;2005</i></small></div>
<div align="right"><small><i>Copyright &copy; Kevlin Henney, 2000-2005</i></small></div>
<div align="right"><small><i>Copyright &copy; Alexander Nasonov, 2006-2010</i></small></div>
<div align="right"><small><i>Copyright &copy; Antony Polukhin, 2011</i></small></div>
<div align="right"><small><i>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</i></small>
</div>
</body>
</html>