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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="boost_lexical_cast.synopsis"></a><a class="link" href="synopsis.html" title="Synopsis">Synopsis</a> |
| </h2></div></div></div> |
| <div class="toc"><dl class="toc"> |
| <dt><span class="section"><a href="synopsis.html#boost_lexical_cast.synopsis.lexical_cast">lexical_cast</a></span></dt> |
| <dt><span class="section"><a href="synopsis.html#boost_lexical_cast.synopsis.bad_lexical_cast">bad_lexical_cast</a></span></dt> |
| <dt><span class="section"><a href="synopsis.html#boost_lexical_cast.synopsis.try_lexical_convert">try_lexical_convert</a></span></dt> |
| </dl></div> |
| <p> |
| Library features defined in <a href="../../../boost/lexical_cast.hpp" target="_top">boost/lexical_cast.hpp</a>: |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> |
| <span class="special">{</span> |
| <span class="keyword">class</span> <span class="identifier">bad_lexical_cast</span><span class="special">;</span> |
| |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Target</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Source</span><span class="special">></span> |
| <span class="identifier">Target</span> <span class="identifier">lexical_cast</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Source</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Target</span><span class="special">></span> |
| <span class="identifier">Target</span> <span class="identifier">lexical_cast</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">AnyCharacterType</span><span class="special">*</span> <span class="identifier">chars</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">count</span><span class="special">);</span> |
| |
| <span class="keyword">namespace</span> <span class="identifier">conversion</span> |
| <span class="special">{</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Target</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Source</span><span class="special">></span> |
| <span class="keyword">bool</span> <span class="identifier">try_lexical_convert</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Source</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">,</span> <span class="identifier">Target</span><span class="special">&</span> <span class="identifier">result</span><span class="special">);</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">AnyCharacterType</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Target</span><span class="special">></span> |
| <span class="keyword">bool</span> <span class="identifier">try_lexical_convert</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">AnyCharacterType</span><span class="special">*</span> <span class="identifier">chars</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">count</span><span class="special">,</span> <span class="identifier">Target</span><span class="special">&</span> <span class="identifier">result</span><span class="special">);</span> |
| |
| <span class="special">}</span> <span class="comment">// namespace conversion</span> |
| <span class="special">}</span> <span class="comment">// namespace boost</span> |
| </pre> |
| <p> |
| </p> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_lexical_cast.synopsis.lexical_cast"></a><a class="link" href="synopsis.html#boost_lexical_cast.synopsis.lexical_cast" title="lexical_cast">lexical_cast</a> |
| </h3></div></div></div> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Target</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Source</span><span class="special">></span> |
| <span class="identifier">Target</span> <span class="identifier">lexical_cast</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Source</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span> |
| </pre> |
| <p> |
| Returns the result of streaming arg into a standard library string-based |
| stream and then out as a Target object. Where Target is either <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> |
| or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">wstring</span></code>, stream extraction takes the whole |
| content of the string, including spaces, rather than relying on the default |
| <code class="computeroutput"><span class="keyword">operator</span><span class="special">>></span></code> |
| behavior. If the conversion is unsuccessful, a <code class="computeroutput"><span class="identifier">bad_lexical_cast</span></code> |
| exception is thrown. |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Target</span><span class="special">></span> |
| <span class="identifier">Target</span> <span class="identifier">lexical_cast</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">AnyCharacterType</span><span class="special">*</span> <span class="identifier">chars</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">count</span><span class="special">);</span> |
| </pre> |
| <p> |
| Takes an array of <code class="computeroutput"><span class="identifier">count</span></code> characters |
| as input parameter and streams them out as a Target object. If the conversion |
| is unsuccessful, a <code class="computeroutput"><span class="identifier">bad_lexical_cast</span></code> |
| exception is thrown. This call may be useful for processing nonzero terminated |
| array of characters or processing just some part of character array. |
| </p> |
| <p> |
| The requirements on the argument and result types for both functions are: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem"> |
| Source is OutputStreamable, meaning that an <code class="computeroutput"><span class="keyword">operator</span><span class="special"><<</span></code> is defined that takes a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">ostream</span></code> or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">wostream</span></code> |
| object on the left hand side and an instance of the argument type on |
| the right. |
| </li> |
| <li class="listitem"> |
| Target is InputStreamable, meaning that an <code class="computeroutput"><span class="keyword">operator</span><span class="special">>></span></code> is defined that takes a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">istream</span></code> or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">wistream</span></code> |
| object on the left hand side and an instance of the result type on the |
| right. |
| </li> |
| <li class="listitem"> |
| Target is CopyConstructible [20.1.3]. |
| </li> |
| <li class="listitem"> |
| Target is DefaultConstructible, meaning that it is possible to default-initialize |
| an object of that type [8.5, 20.1.4]. |
| </li> |
| </ul></div> |
| <p> |
| The character type of the underlying stream is assumed to be <code class="computeroutput"><span class="keyword">char</span></code> unless either the <code class="computeroutput"><span class="identifier">Source</span></code> |
| or the <code class="computeroutput"><span class="identifier">Target</span></code> requires wide-character |
| streaming, in which case the underlying stream uses <code class="computeroutput"><span class="keyword">wchar_t</span></code>. |
| Following types also can use <code class="computeroutput"><span class="keyword">char16_t</span></code> |
| or <code class="computeroutput"><span class="keyword">char32_t</span></code> for wide-character |
| streaming: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem"> |
| Single character: <code class="computeroutput"><span class="keyword">char16_t</span></code>, |
| <code class="computeroutput"><span class="keyword">char32_t</span></code> |
| </li> |
| <li class="listitem"> |
| Arrays of characters: <code class="computeroutput"><span class="keyword">char16_t</span> |
| <span class="special">*</span></code>, <code class="computeroutput"><span class="keyword">char32_t</span> |
| <span class="special">*</span></code>, <code class="computeroutput"><span class="keyword">const</span> |
| <span class="keyword">char16_t</span> <span class="special">*</span></code>, |
| <code class="computeroutput"><span class="keyword">const</span> <span class="keyword">char32_t</span> |
| <span class="special">*</span></code> |
| </li> |
| <li class="listitem"> |
| Strings: <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_string</span></code>, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">containers</span><span class="special">::</span><span class="identifier">basic_string</span></code> |
| </li> |
| <li class="listitem"> |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">iterator_range</span><span class="special"><</span><span class="identifier">WideCharPtr</span><span class="special">></span></code>, |
| where <code class="computeroutput"><span class="identifier">WideCharPtr</span></code> is |
| a pointer to wide-character or pointer to const wide-character |
| </li> |
| <li class="listitem"> |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="identifier">CharT</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span></code> |
| and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="identifier">CharT</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span></code>, |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">CharT</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span></code> and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">CharT</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span></code> |
| </li> |
| </ul></div> |
| <div class="important"><table border="0" summary="Important"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../doc/src/images/important.png"></td> |
| <th align="left">Important</th> |
| </tr> |
| <tr><td align="left" valign="top"> |
| <p> |
| Many compilers and runtime libraries fail to make conversions using new |
| Unicode characters. Make sure that the following code compiles and outputs |
| nonzero values, before using new types: |
| </p> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> |
| <span class="special"><<</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">u32string</span><span class="special">>(</span><span class="number">1.0</span><span class="special">).</span><span class="identifier">size</span><span class="special">()</span> |
| <span class="special"><<</span> <span class="string">" "</span> |
| <span class="special"><<</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">u16string</span><span class="special">>(</span><span class="number">1.0</span><span class="special">).</span><span class="identifier">size</span><span class="special">();</span> |
| </pre> |
| <p> |
| </p> |
| </td></tr> |
| </table></div> |
| <p> |
| Where a higher degree of control is required over conversions, <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">stringstream</span></code> |
| and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">wstringstream</span></code> offer a more appropriate |
| path. Where non-stream-based conversions are required, <code class="computeroutput"><span class="identifier">lexical_cast</span></code> |
| is the wrong tool for the job and is not special-cased for such scenarios. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_lexical_cast.synopsis.bad_lexical_cast"></a><a class="link" href="synopsis.html#boost_lexical_cast.synopsis.bad_lexical_cast" title="bad_lexical_cast">bad_lexical_cast</a> |
| </h3></div></div></div> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">bad_lexical_cast</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">bad_cast</span> |
| <span class="special">{</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="special">...</span> <span class="comment">// same member function interface as std::exception</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| Exception used to indicate runtime lexical_cast failure. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_lexical_cast.synopsis.try_lexical_convert"></a><a class="link" href="synopsis.html#boost_lexical_cast.synopsis.try_lexical_convert" title="try_lexical_convert">try_lexical_convert</a> |
| </h3></div></div></div> |
| <p> |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code> remains the main interface |
| for lexical conversions. It must be used by default in most cases. However |
| some developers wish to make their own conversion functions, reusing all |
| the optimizations of the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code>. |
| That's where the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">conversion</span><span class="special">::</span><span class="identifier">try_lexical_convert</span></code> function steps in. |
| </p> |
| <p> |
| <code class="computeroutput"><span class="identifier">try_lexical_convert</span></code> returns |
| <code class="computeroutput"><span class="keyword">true</span></code> if conversion succeeded, |
| otherwise returns <code class="computeroutput"><span class="keyword">false</span></code>. If |
| conversion failed and <code class="computeroutput"><span class="keyword">false</span></code> |
| was returned, state of <code class="computeroutput"><span class="identifier">result</span></code> |
| output variable is undefined. |
| </p> |
| <p> |
| Actually, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code> is implemented using <code class="computeroutput"><span class="identifier">try_lexical_convert</span></code>: |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Target</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Source</span><span class="special">></span> |
| <span class="keyword">inline</span> <span class="identifier">Target</span> <span class="identifier">lexical_cast</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Source</span> <span class="special">&</span><span class="identifier">arg</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">Target</span> <span class="identifier">result</span><span class="special">;</span> |
| |
| <span class="keyword">if</span> <span class="special">(!</span><span class="identifier">conversion</span><span class="special">::</span><span class="identifier">try_lexical_convert</span><span class="special">(</span><span class="identifier">arg</span><span class="special">,</span> <span class="identifier">result</span><span class="special">))</span> |
| <span class="keyword">throw</span> <span class="identifier">bad_lexical_cast</span><span class="special">();</span> |
| |
| <span class="keyword">return</span> <span class="identifier">result</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| <code class="computeroutput"><span class="identifier">try_lexical_convert</span></code> relaxes |
| the CopyConstructible and DefaultConstructible requirements for <code class="computeroutput"><span class="identifier">Target</span></code> type. Following requirements for |
| <code class="computeroutput"><span class="identifier">Target</span></code> and <code class="computeroutput"><span class="identifier">Source</span></code> remain: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem"> |
| Source must be OutputStreamable, meaning that an <code class="computeroutput"><span class="keyword">operator</span><span class="special"><<</span></code> is defined that takes a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">ostream</span></code> or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">wostream</span></code> |
| object on the left hand side and an instance of the argument type on |
| the right. |
| </li> |
| <li class="listitem"> |
| Target must be InputStreamable, meaning that an <code class="computeroutput"><span class="keyword">operator</span><span class="special">>></span></code> is defined that takes a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">istream</span></code> or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">wistream</span></code> |
| object on the left hand side and an instance of the result type on the |
| right. |
| </li> |
| </ul></div> |
| </div> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2000-2005 Kevlin Henney<br>Copyright © 2006-2010 Alexander Nasonov<br>Copyright © 2011-2014 Antony |
| Polukhin<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
| </p> |
| </div></td> |
| </tr></table> |
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