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-<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 7. Strings</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><meta name="keywords" content=" ISO C++ , library "/><link rel="home" href="../spine.html" title="The GNU C++ Library"/><link rel="up" href="bk01pt02.html" title="Part II. Standard Contents"/><link rel="prev" href="traits.html" title="Traits"/><link rel="next" href="localization.html" title="Chapter 8. Localization"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 7.
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Strings
-</th></tr><tr><td align="left"><a accesskey="p" href="traits.html">Prev</a> </td><th width="60%" align="center">Part II.
+</th></tr><tr><td
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Standard Contents
- </th><td align="right"> <a accesskey="n" href="localization.html">Next</a></td></tr></table><hr/></div><div class="chapter" title="Chapter 7. Strings"><div class="titlepage"><div><div><h2 class="title"><a id="std.strings"/>Chapter 7.
+ </th><td width="20%" align="right"> <a accesskey="n" href="localization.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="std.strings"></a>Chapter 7.
Strings
- <a id="id475084" class="indexterm"/>
-</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl
><dt><span class="section"><a href="strings.html#std.strings.string">String Classes</a></span></dt><dd><dl><dt><span class="section"><a href="strings.html#strings.string.simple">Simple Transformations</a></span></dt><dt><span class="section"><a href="strings.html#strings.string.case">Case Sensitivity</a></span></dt><dt><span class="section"><a href="strings.html#strings.string.character_types">Arbitrary Character Types</a></span></dt><dt><span class="section"><a href="strings.html#strings.string.token">Tokenizing</a></span></dt><dt><span class="section"><a href="strings.html#strings.string.shrink">Shrink to Fit</a></span></dt><dt><span class="section"><a href="strings.html#strings.string.Cstring">CString (MFC)</a></span></dt></dl></dd></dl></div><div class="section" title="String Classes"><div class="titlepage"><div><div><h2 class="title"><a id="std.strings.string"/>String Classes</h2></div></div></div><div class="section" title="Simple Transformations"><div class="titlepage"><div><div><h3 class="title"><a id="strings.string.simple"/>Simple Transformations</h3></div></div></div><p>
+ <a id="idm269986623744" class="indexterm"></a>
+</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl
class="toc"><dt><span class="section"><a href="strings.html#std.strings.string">String Classes</a></span></dt><dd><dl><dt><span class="section"><a href="strings.html#strings.string.simple">Simple Transformations</a></span></dt><dt><span class="section"><a href="strings.html#strings.string.case">Case Sensitivity</a></span></dt><dt><span class="section"><a href="strings.html#strings.string.character_types">Arbitrary Character Types</a></span></dt><dt><span class="section"><a href="strings.html#strings.string.token">Tokenizing</a></span></dt><dt><span class="section"><a href="strings.html#strings.string.shrink">Shrink to Fit</a></span></dt><dt><span class="section"><a href="strings.html#strings.string.Cstring">CString (MFC)</a></span></dt></dl></dd></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="std.strings.string"></a>String Classes</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="strings.string.simple"></a>Simple Transformations</h3></div></div></div><p>
Here are Standard, simple, and portable ways to perform common
transformations on a <code class="code">string</code> instance, such as
"convert to all upper case." The word transformations
are overloaded names (declared in <code class="code"><cctype></code> and
<code class="code"><locale></code>) so the template-arguments for
<code class="code">transform<></code> cannot be deduced, as explained in
- <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2002-11/msg00180.html">this
+ <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2002-11/msg00180.html" target="_top">this
message</a>.
At minimum, you can write short wrappers like
str.erase(notwhite+1); </pre><p>Obviously, the calls to <code class="code">find</code> could be inserted directly
into the calls to <code class="code">erase</code>, in case your compiler does not
optimize named temporaries out of existence.
- </p></div><div class="section"
title="Case Sensitivity"><div class="titlepage"><div><div><h3 class="title"><a id="strings.string.case"/>Case Sensitivity</h3></div></div></div><p>
+ </p></div><div class="section"
><div class="titlepage"><div><div><h3 class="title"><a id="strings.string.case"></a>Case Sensitivity</h3></div></div></div><p>
</p><p>The well-known-and-if-it-isn't-well-known-it-ought-to-be
- <a class="link" href="http://www.gotw.ca/gotw/">Guru of the Week</a>
+ <a class="link" href="http://www.gotw.ca/gotw/" target="_top">Guru of the Week</a>
discussions held on Usenet covered this topic in January of 1998.
Briefly, the challenge was, <span class="quote">“<span class="quote">write a 'ci_string' class which
is identical to the standard 'string' class, but is
assert( strcmp( s.c_str(), "AbCdE" ) == 0 );
assert( strcmp( s.c_str(), "abcde" ) != 0 ); </pre><p>The solution is surprisingly easy. The original answer was
posted on Usenet, and a revised version appears in Herb Sutter's
- book <span class="emphasis"><em>Exceptional C++</em></span> and on his website as <a class="link" href="http://www.gotw.ca/gotw/029.htm">GotW 29</a>.
+ book <span class="emphasis"><em>Exceptional C++</em></span> and on his website as <a class="link" href="http://www.gotw.ca/gotw/029.htm" target="_top">GotW 29</a>.
</p><p>See? Told you it was easy!</p><p>
<span class="emphasis"><em>Added June 2000:</em></span> The May 2000 issue of C++
- Report contains a fascinating <a class="link" href="http://lafstern.org/matt/col2_new.pdf"> article</a> by
+ Report contains a fascinating <a class="link" href="http://lafstern.org/matt/col2_new.pdf" target="_top"> article</a> by
Matt Austern (yes, <span class="emphasis"><em>the</em></span> Matt Austern) on why
case-insensitive comparisons are not as easy as they seem, and
why creating a class is the <span class="emphasis"><em>wrong</em></span> way to go
that nobody ever called me on it...) The GotW question and answer
remain useful instructional tools, however.
</p><p><span class="emphasis"><em>Added September 2000:</em></span> James Kanze provided a link to a
- <a class="link" href="http://www.unicode.org/reports/tr21/tr21-5.html">Unicode
+ <a class="link" href="http://www.unicode.org/reports/tr21/tr21-5.html" target="_top">Unicode
Technical Report discussing case handling</a>, which provides some
very good information.
- </p></div><div class="section"
title="Arbitrary Character Types"><div class="titlepage"><div><div><h3 class="title"><a id="strings.string.character_types"/>Arbitrary Character Types</h3></div></div></div><p>
+ </p></div><div class="section"
><div class="titlepage"><div><div><h3 class="title"><a id="strings.string.character_types"></a>Arbitrary Character Types</h3></div></div></div><p>
</p><p>The <code class="code">std::basic_string</code> is tantalizingly general, in that
it is parameterized on the type of the characters which it holds.
In theory, you could whip up a Unicode character class and instantiate
works and can be specialized even for <code class="code">int</code> and other
built-in types.
</p><p>If you want to use your own special character class, then you have
- <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2002-08/msg00163.html">a lot
+ <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2002-08/msg00163.html" target="_top">a lot
of work to do</a>, especially if you with to use i18n features
(facets require traits information but don't have a traits argument).
- </p><p>Another example of how to specialize char_traits was given <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2002-08/msg00260.html">on the
+ </p><p>Another example of how to specialize char_traits was given <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2002-08/msg00260.html" target="_top">on the
mailing list</a> and at a later date was put into the file <code class="code">
include/ext/pod_char_traits.h</code>. We agree
that the way it's used with basic_string (scroll down to main())
- doesn't look nice, but that's because <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2002-08/msg00236.html">the
- nice-looking first attempt</a> turned out to <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2002-08/msg00242.html">not
+ doesn't look nice, but that's because <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2002-08/msg00236.html" target="_top">the
+ nice-looking first attempt</a> turned out to <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2002-08/msg00242.html" target="_top">not
be conforming C++</a>, due to the rule that CharT must be a POD.
(See how tricky this is?)
- </p></div><div class="section"
title="Tokenizing"><div class="titlepage"><div><div><h3 class="title"><a id="strings.string.token"/>Tokenizing</h3></div></div></div><p>
+ </p></div><div class="section"
><div class="titlepage"><div><div><h3 class="title"><a id="strings.string.token"></a>Tokenizing</h3></div></div></div><p>
</p><p>The Standard C (and C++) function <code class="code">strtok()</code> leaves a lot to
be desired in terms of user-friendliness. It's unintuitive, it
destroys the character string on which it operates, and it requires
tokenizing as well. Build an istringstream from the input text,
and then use std::getline with varying delimiters (the three-argument
signature) to extract tokens into a string.
- </p></div><div class="section"
title="Shrink to Fit"><div class="titlepage"><div><div><h3 class="title"><a id="strings.string.shrink"/>Shrink to Fit</h3></div></div></div><p>
+ </p></div><div class="section"
><div class="titlepage"><div><div><h3 class="title"><a id="strings.string.shrink"></a>Shrink to Fit</h3></div></div></div><p>
</p><p>From GCC 3.4 calling <code class="code">s.reserve(res)</code> on a
<code class="code">string s</code> with <code class="code">res < s.capacity()</code> will
reduce the string's capacity to <code class="code">std::max(s.size(), res)</code>.
(see <a class="link" href="../faq.html#faq.size_equals_capacity" title="7.8.">this FAQ
entry</a>) but the regular copy constructor cannot be used
because libstdc++'s <code class="code">string</code> is Copy-On-Write.
- </p><p>In <a class="link" href="status.html#status.iso.200x" title="C++ 200x">C++0x</a> mode you can call
+ </p><p>In <a class="link" href="status.html#status.iso.2011" title="C++ 2011">C++11</a> mode you can call
<code class="code">s.shrink_to_fit()</code> to achieve the same effect as
<code class="code">s.reserve(s.size())</code>.
- </p></div><div class="section"
title="CString (MFC)"><div class="titlepage"><div><div><h3 class="title"><a id="strings.string.Cstring"/>CString (MFC)</h3></div></div></div><p>
+ </p></div><div class="section"
><div class="titlepage"><div><div><h3 class="title"><a id="strings.string.Cstring"></a>CString (MFC)</h3></div></div></div><p>
</p><p>A common lament seen in various newsgroups deals with the Standard
string class as opposed to the Microsoft Foundation Class called
CString. Often programmers realize that a standard portable
their application from a Win32 platform, they discover that they
are relying on special functions offered by the CString class.
</p><p>Things are not as bad as they seem. In
- <a class="link" href="http://gcc.gnu.org/ml/gcc/1999-04n/msg00236.html">this
+ <a class="link" href="http://gcc.gnu.org/ml/gcc/1999-04n/msg00236.html" target="_top">this
message</a>, Joe Buck points out a few very important things:
- </p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>The Standard <code class="code">string</code> supports all the operations
+ </p><div class="itemizedlist"><ul class="itemizedlist"
style="list-style-type: disc; "><li class="listitem"><p>The Standard <code class="code">string</code> supports all the operations
that CString does, with three exceptions.
</p></li><li class="listitem"><p>Two of those exceptions (whitespace trimming and case
conversion) are trivial to implement. In fact, we do so
performance is O(n).
</pre><p>Joe Buck also pointed out some other things to keep in mind when
comparing CString and the Standard string class:
- </p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>CString permits access to its internal representation; coders
+ </p><div class="itemizedlist"><ul class="itemizedlist"
style="list-style-type: disc; "><li class="listitem"><p>CString permits access to its internal representation; coders
who exploited that may have problems moving to <code class="code">string</code>.
</p></li><li class="listitem"><p>Microsoft ships the source to CString (in the files
MFC\SRC\Str{core,ex}.cpp), so you could fix the allocation
libstdc++ string, the SGI string, and the SGI rope, and this
is all before any allocator or traits customizations! (More
choices than you can shake a stick at -- want fries with that?)
- </p></li></ul></div></div></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="traits.html">Prev</a> </td><td align="center"><a accesskey="u" href="bk01pt02.html">Up</a></td><td align="right"> <a accesskey="n" href="localization.html">Next</a></td></tr><tr><td align="left" valign="top">Traits </td><td align="center"><a accesskey="h" href="../spine.html">Home</a></td><td align="right" valign="top"> Chapter 8.
+ </p></li></ul></div></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="traits.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="bk01pt02.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="localization.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Traits </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 8.
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