boostorg/conversion
1
0
Fork 1
mirror of https://github.com/boostorg/conversion.git synced 2025-08-02 14:04:28 +02:00
Code Issues Packages Projects Releases Wiki Activity

Merged from trunk revision 71922. Most part of this modifications of lexical_cast library were made and successfully tested during the year 2009.

Browse Source 
Later commits affected only documentation bugs.

[SVN r71923]
This commit is contained in:
Antony Polukhin
2011-05-13 17:44:51 +00:00
parent b5583b88fa
commit 701d5f0bf0
3 changed files with 86 additions and 29 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
include/boost/lexical_cast.hpp
View File

@@ -55,7 +55,13 @@
namespace boost
{
// exception used to indicate runtime lexical_cast failure
class bad_lexical_cast : public std::bad_cast
class bad_lexical_cast :
// workaround MSVC bug with std::bad_cast when _HAS_EXCEPTIONS == 0
#if defined(BOOST_MSVC) && defined(_HAS_EXCEPTIONS) && !_HAS_EXCEPTIONS
public std::exception
#else
public std::bad_cast
#endif
#if defined(__BORLANDC__) && BOOST_WORKAROUND( __BORLANDC__, < 0x560 )
// under bcc32 5.5.1 bad_cast doesn't derive from exception
@@ -521,11 +527,10 @@ namespace boost
std::string::size_type const grouping_size = grouping.size();
CharT thousands_sep = grouping_size ? np.thousands_sep() : 0;
std::string::size_type group = 0; // current group number
char last_grp_size = grouping[0] <= 0 ? CHAR_MAX : grouping[0];
// a) Since grouping is const, grouping[grouping.size()] returns 0.
// b) It's safe to assume here and below that CHAR_MAX
// is equivalent to unlimited grouping:
char last_grp_size =
grouping_size == 0 || grouping[0] <= 0 ? CHAR_MAX : grouping[0];
#ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
// Check that ulimited group is unreachable:
BOOST_STATIC_ASSERT(std::numeric_limits<T>::digits10 < CHAR_MAX);
#endif
@@ -1120,6 +1125,7 @@ namespace boost
# pragma warning( push )
# pragma warning( disable : 4701 ) // possible use of ... before initialization
# pragma warning( disable : 4702 ) // unreachable code
# pragma warning( disable : 4267 ) // conversion from 'size_t' to 'unsigned int'
#endif
template< typename Target
@@ -1191,11 +1197,7 @@ namespace boost
Target result;
if(!(interpreter << arg && interpreter >> result))
#ifndef BOOST_NO_TYPEID
throw_exception(bad_lexical_cast(typeid(Source), typeid(Target)));
#else
throw_exception(bad_lexical_cast());
#endif
BOOST_LCAST_THROW_BAD_CAST(Source, Target);
return result;
}

84
lexical_cast.htm
View File

@@ -194,32 +194,74 @@ public:
</pre>
</blockquote>Exception used to indicate runtime <a href="#lexical_cast"><code>lexical_cast</code></a>
failure.
<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>.
<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>
or,
<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</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>
<tr>
<td valign="top"><b>Question:</b></td>
<td>Why <code>std::cout << boost::lexical_cast&lt;unsigned int&gt;("-1");</code> does not throw, but outputs 4294967295?</td>
</tr>
<tr>
<td valign="top"><b>Answer:</b></td>
<td><code>boost::lexical_cast</code> has the behavior of <code>stringstream</code>, which uses <code>num_get</code> functions of <code>std::locale</code> to convert numbers. If we look at the [22.2.2.1.2] of Programming languages &mdash; C++, we'll see, that <code>num_get</code> uses the rules of <code>scanf</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.
</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://www.accu.org/var/uploads/journals/overload74.pdf">Overload #74</a>,
<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>),
August 2006.</li>
</ul>
<h2><a name="changes">Changes</a></h2>
@@ -265,6 +307,12 @@ public:
<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>

7
lexical_cast_test.cpp
View File

@@ -11,6 +11,13 @@
//
// Note: The unit test no longer compile on MSVC 6, but lexical_cast itself works for it.
//
// We need this #define before any #includes: otherwise msvc will emit warnings
// deep within std::string, resulting from our (perfectly legal) use of basic_string
// with a custom traits class:
//
#define _SCL_SECURE_NO_WARNINGS
#include <boost/config.hpp>
#if defined(__INTEL_COMPILER)