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diff --git a/doc/html/boost_lexical_cast/frequently_asked_questions.html b/doc/html/boost_lexical_cast/frequently_asked_questions.html new file mode 100755 index 0000000000..c52e0af64b --- /dev/null +++ b/doc/html/boost_lexical_cast/frequently_asked_questions.html @@ -0,0 +1,128 @@ +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>Frequently Asked Questions</title> +<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> +<meta name="generator" content="DocBook XSL Stylesheets V1.76.1"> +<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> +<link rel="up" href="../boost_lexical_cast.html" title="Chapter 15. Boost.Lexical_Cast 1.0"> +<link rel="prev" href="synopsis.html" title="Synopsis"> +<link rel="next" href="changes.html" title="Changes"> +</head> +<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> +<table cellpadding="2" width="100%"><tr> +<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> +<td align="center"><a href="../../../index.html">Home</a></td> +<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> +<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> +<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> +<td align="center"><a href="../../../more/index.htm">More</a></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="synopsis.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../boost_lexical_cast.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="changes.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +<div class="section"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="boost_lexical_cast.frequently_asked_questions"></a><a class="link" href="frequently_asked_questions.html" title="Frequently Asked Questions">Frequently + Asked Questions</a> +</h2></div></div></div> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> + <span class="bold"><strong>Question:</strong></span> Why does <code class="computeroutput"><span class="identifier">lexical_cast</span><span class="special"><</span><span class="identifier">int8_t</span><span class="special">>(</span><span class="string">"127"</span><span class="special">)</span></code> throw <code class="computeroutput"><span class="identifier">bad_lexical_cast</span></code>? + <div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"> + <span class="bold"><strong>Answer:</strong></span> The type <code class="computeroutput"><span class="identifier">int8_t</span></code> + is a <code class="computeroutput"><span class="keyword">typedef</span></code> to <code class="computeroutput"><span class="keyword">char</span></code> or <code class="computeroutput"><span class="keyword">signed</span> + <span class="keyword">char</span></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. Please use other + integer types such as <code class="computeroutput"><span class="keyword">int</span></code> + or <code class="computeroutput"><span class="keyword">short</span> <span class="keyword">int</span></code>. + If bounds checking is important, you can also call <a href="../../../libs/numeric/conversion/doc/html/boost_numericconversion/improved_numeric_cast__.html" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">numeric_cast</span></code></a>: <code class="computeroutput"><span class="identifier">numeric_cast</span><span class="special"><</span><span class="identifier">int8_t</span><span class="special">>(</span><span class="identifier">lexical_cast</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"127"</span><span class="special">));</span></code> + </li></ul></div> + </li></ul></div> +<pre class="programlisting"></pre> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> + <span class="bold"><strong>Question:</strong></span> Why does <code class="computeroutput"><span class="identifier">lexical_cast</span><span class="special"><</span><span class="keyword">unsigned</span> <span class="keyword">char</span><span class="special">>(</span><span class="string">"127"</span><span class="special">)</span></code> + throw <code class="computeroutput"><span class="identifier">bad_lexical_cast</span></code>? + <div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"> + <span class="bold"><strong>Answer:</strong></span> Lexical conversion to any + char type is simply reading a byte from source. But since the source + has more than one byte, the exception is thrown. Please use other + integer types such as <code class="computeroutput"><span class="keyword">int</span></code> + or <code class="computeroutput"><span class="keyword">short</span> <span class="keyword">int</span></code>. + If bounds checking is important, you can also call <a href="../../../libs/numeric/conversion/doc/html/boost_numericconversion/improved_numeric_cast__.html" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">numeric_cast</span></code></a>: <code class="computeroutput"><span class="identifier">numeric_cast</span><span class="special"><</span><span class="keyword">unsigned</span> <span class="keyword">char</span><span class="special">>(</span><span class="identifier">lexical_cast</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"127"</span><span class="special">));</span></code> + </li></ul></div> + </li></ul></div> +<pre class="programlisting"></pre> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> + <span class="bold"><strong>Question:</strong></span> What does <code class="computeroutput"><span class="identifier">lexical_cast</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">></span></code> of an <code class="computeroutput"><span class="identifier">int8_t</span></code> + or <code class="computeroutput"><span class="identifier">uint8_t</span></code> not do what + I expect? + <div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"> + <span class="bold"><strong>Answer:</strong></span> As above, note that int8_t + and uint8_t are actually chars and are formatted as such. To avoid + this, cast to an integer type first: <code class="computeroutput"><span class="identifier">lexical_cast</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>(</span><span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="identifier">n</span><span class="special">));</span></code> + </li></ul></div> + </li></ul></div> +<pre class="programlisting"></pre> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> + <span class="bold"><strong>Question:</strong></span> The implementation always resets + the <code class="computeroutput"><span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">skipws</span></code> flag of an underlying stream object. + It breaks my <code class="computeroutput"><span class="keyword">operator</span><span class="special">>></span></code> + that works only in presence of this flag. Can you remove code that resets + the flag? + <div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"> + <span class="bold"><strong>Answer:</strong></span> May be in a future version. + There is no requirement in <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1973.html" target="_top">Lexical + Conversion Library Proposal for TR2, N1973 by Kevlin Henney and Beman + Dawes</a> to reset the flag but remember that <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1973.html" target="_top">Lexical + Conversion Library Proposal for TR2, N1973</a> is not yet accepted + by the committee. By the way, it's a great opportunity to make your + <code class="computeroutput"><span class="keyword">operator</span><span class="special">>></span></code> + conform to the standard. Read a good C++ book, study <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">sentry</span></code> and <a href="../../../libs/io/doc/ios_state.html" target="_top"><code class="computeroutput"><span class="identifier">ios_state_saver</span></code></a>. + </li></ul></div> + </li></ul></div> +<pre class="programlisting"></pre> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> + <span class="bold"><strong>Question:</strong></span> Why <code class="computeroutput"><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="keyword">unsigned</span> <span class="keyword">int</span><span class="special">>(</span><span class="string">"-1"</span><span class="special">);</span></code> + does not throw, but outputs 4294967295? + <div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"> + <span class="bold"><strong>Answer:</strong></span> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code> + has the behavior of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">stringstream</span></code>, + which uses <code class="computeroutput"><span class="identifier">num_get</span></code> + functions of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">locale</span></code> + to convert numbers. If we look at the Programming languages — C++, + we'll see, that <code class="computeroutput"><span class="identifier">num_get</span></code> + uses the rules of <code class="computeroutput"><span class="identifier">scanf</span></code> + for conversions. And in the C99 standard for unsigned input value + minus sign is optional, so if a negative number is read, no errors + will arise and the result will be the two's complement. + </li></ul></div> + </li></ul></div> +<pre class="programlisting"></pre> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> + <span class="bold"><strong>Question:</strong></span> Why <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="identifier">L</span><span class="char">'A'</span><span class="special">);</span></code> outputs + 65 and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span><span class="special"><</span><span class="keyword">wchar_t</span><span class="special">>(</span><span class="identifier">L</span><span class="string">"65"</span><span class="special">);</span></code> does not throw? + <div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"> + <span class="bold"><strong>Answer:</strong></span> If you are using an old + version of Visual Studio or compile code with /Zc:wchar_t- flag, + <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code> sees single <code class="computeroutput"><span class="keyword">wchar_t</span></code> character as <code class="computeroutput"><span class="keyword">unsigned</span> <span class="keyword">short</span></code>. + It is not a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code> + mistake, but a limitation of compiler options that you use. + </li></ul></div> + </li></ul></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 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> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="synopsis.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../boost_lexical_cast.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="changes.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> |