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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 13. String Classes</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="strings.html" title="Part V. Strings" /><link rel="prev" href="strings.html" title="Part V. Strings" /><link rel="next" href="bk01pt05ch13s02.html" title="Case Sensitivity" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 13. String Classes</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="strings.html">Prev</a> </td><th width="60%" align="center">Part V.
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Strings
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</th><td width="20%" align="right"> <a accesskey="n" href="bk01pt05ch13s02.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 13. String Classes"><div class="titlepage"><div><div><h2 class="title"><a id="manual.strings.string"></a>Chapter 13. String Classes</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="bk01pt05ch13.html#strings.string.simple">Simple Transformations</a></span></dt><dt><span class="sect1"><a href="bk01pt05ch13s02.html">Case Sensitivity</a></span></dt><dt><span class="sect1"><a href="bk01pt05ch13s03.html">Arbitrary Character Types</a></span></dt><dt><span class="sect1"><a href="bk01pt05ch13s04.html">Tokenizing</a></span></dt><dt><span class="sect1"><a href="bk01pt05ch13s05.html">Shrink to Fit</a></span></dt><dt><span class="sect1"><a href="bk01pt05ch13s06.html">CString (MFC)</a></span></dt></dl></div><div class="sect1" title="Simple Transformations"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="strings.string.simple"></a>Simple Transformations</h2></div></div></div><p>
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Here are Standard, simple, and portable ways to perform common
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transformations on a <code class="code">string</code> instance, such as
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"convert to all upper case." The word transformations
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is especially apt, because the standard template function
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<code class="code">transform<></code> is used.
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</p><p>
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This code will go through some iterations. Here's a simple
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version:
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</p><pre class="programlisting">
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#include <string>
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#include <algorithm>
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#include <cctype> // old <ctype.h>
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struct ToLower
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{
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char operator() (char c) const { return std::tolower(c); }
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};
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struct ToUpper
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{
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char operator() (char c) const { return std::toupper(c); }
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};
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int main()
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{
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std::string s ("Some Kind Of Initial Input Goes Here");
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// Change everything into upper case
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std::transform (s.begin(), s.end(), s.begin(), ToUpper());
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// Change everything into lower case
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std::transform (s.begin(), s.end(), s.begin(), ToLower());
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// Change everything back into upper case, but store the
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// result in a different string
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std::string capital_s;
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capital_s.resize(s.size());
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std::transform (s.begin(), s.end(), capital_s.begin(), ToUpper());
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}
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</pre><p>
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<span class="emphasis"><em>Note</em></span> that these calls all
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involve the global C locale through the use of the C functions
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<code class="code">toupper/tolower</code>. This is absolutely guaranteed to work --
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but <span class="emphasis"><em>only</em></span> if the string contains <span class="emphasis"><em>only</em></span> characters
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from the basic source character set, and there are <span class="emphasis"><em>only</em></span>
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96 of those. Which means that not even all English text can be
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represented (certain British spellings, proper names, and so forth).
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So, if all your input forevermore consists of only those 96
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characters (hahahahahaha), then you're done.
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</p><p><span class="emphasis"><em>Note</em></span> that the
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<code class="code">ToUpper</code> and <code class="code">ToLower</code> function objects
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are needed because <code class="code">toupper</code> and <code class="code">tolower</code>
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are overloaded names (declared in <code class="code"><cctype></code> and
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<code class="code"><locale></code>) so the template-arguments for
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<code class="code">transform<></code> cannot be deduced, as explained in
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<a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2002-11/msg00180.html" target="_top">this
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message</a>.
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At minimum, you can write short wrappers like
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</p><pre class="programlisting">
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char toLower (char c)
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{
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return std::tolower(c);
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} </pre><p>(Thanks to James Kanze for assistance and suggestions on all of this.)
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</p><p>Another common operation is trimming off excess whitespace. Much
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like transformations, this task is trivial with the use of string's
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<code class="code">find</code> family. These examples are broken into multiple
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statements for readability:
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</p><pre class="programlisting">
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std::string str (" \t blah blah blah \n ");
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// trim leading whitespace
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string::size_type notwhite = str.find_first_not_of(" \t\n");
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str.erase(0,notwhite);
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// trim trailing whitespace
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notwhite = str.find_last_not_of(" \t\n");
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str.erase(notwhite+1); </pre><p>Obviously, the calls to <code class="code">find</code> could be inserted directly
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into the calls to <code class="code">erase</code>, in case your compiler does not
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optimize named temporaries out of existence.
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</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="strings.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="strings.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="bk01pt05ch13s02.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Part V.
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Strings
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</td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Case Sensitivity</td></tr></table></div></body></html>
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