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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 V1.74.0" /><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.
+ Strings
+
+</th><td width="20%" align="right"> <a accesskey="n" href="bk01pt05ch13s02.html">Next</a></td></tr></table><hr /></div><div class="chapter" lang="en" xml:lang="en"><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" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="strings.string.simple"></a>Simple Transformations</h2></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
+ is especially apt, because the standard template function
+ <code class="code">transform<></code> is used.
+ </p><p>
+ This code will go through some iterations. Here's a simple
+ version:
+ </p><pre class="programlisting">
+ #include <string>
+ #include <algorithm>
+ #include <cctype> // old <ctype.h>
+
+ struct ToLower
+ {
+ char operator() (char c) const { return std::tolower(c); }
+ };
+
+ struct ToUpper
+ {
+ char operator() (char c) const { return std::toupper(c); }
+ };
+
+ int main()
+ {
+ std::string s ("Some Kind Of Initial Input Goes Here");
+
+ // Change everything into upper case
+ std::transform (s.begin(), s.end(), s.begin(), ToUpper());
+
+ // Change everything into lower case
+ std::transform (s.begin(), s.end(), s.begin(), ToLower());
+
+ // Change everything back into upper case, but store the
+ // result in a different string
+ std::string capital_s;
+ capital_s.resize(s.size());
+ std::transform (s.begin(), s.end(), capital_s.begin(), ToUpper());
+ }
+ </pre><p>
+ <span class="emphasis"><em>Note</em></span> that these calls all
+ involve the global C locale through the use of the C functions
+ <code class="code">toupper/tolower</code>. This is absolutely guaranteed to work --
+ but <span class="emphasis"><em>only</em></span> if the string contains <span class="emphasis"><em>only</em></span> characters
+ from the basic source character set, and there are <span class="emphasis"><em>only</em></span>
+ 96 of those. Which means that not even all English text can be
+ represented (certain British spellings, proper names, and so forth).
+ So, if all your input forevermore consists of only those 96
+ characters (hahahahahaha), then you're done.
+ </p><p><span class="emphasis"><em>Note</em></span> that the
+ <code class="code">ToUpper</code> and <code class="code">ToLower</code> function objects
+ are needed because <code class="code">toupper</code> and <code class="code">tolower</code>
+ 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="ulink" href="http://gcc.gnu.org/ml/libstdc++/2002-11/msg00180.html" target="_top">this
+ message</a>.
+
+ At minimum, you can write short wrappers like
+ </p><pre class="programlisting">
+ char toLower (char c)
+ {
+ return std::tolower(c);
+ } </pre><p>The correct method is to use a facet for a particular locale
+ and call its conversion functions. These are discussed more in
+ Chapter 22; the specific part is
+ <a class="ulink" href="../22_locale/howto.html#7" target="_top">Correct Transformations</a>,
+ which shows the final version of this code. (Thanks to James Kanze
+ for assistance and suggestions on all of this.)
+ </p><p>Another common operation is trimming off excess whitespace. Much
+ like transformations, this task is trivial with the use of string's
+ <code class="code">find</code> family. These examples are broken into multiple
+ statements for readability:
+ </p><pre class="programlisting">
+ std::string str (" \t blah blah blah \n ");
+
+ // trim leading whitespace
+ string::size_type notwhite = str.find_first_not_of(" \t\n");
+ str.erase(0,notwhite);
+
+ // trim trailing whitespace
+ notwhite = str.find_last_not_of(" \t\n");
+ 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><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.
+ Strings
+
+ </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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