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3 <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.
6 </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>
7 Here are Standard, simple, and portable ways to perform common
8 transformations on a <code class="code">string</code> instance, such as
9 "convert to all upper case." The word transformations
10 is especially apt, because the standard template function
11 <code class="code">transform<></code> is used.
13 This code will go through some iterations. Here's a simple
15 </p><pre class="programlisting">
16 #include <string>
17 #include <algorithm>
18 #include <cctype> // old <ctype.h>
22 char operator() (char c) const { return std::tolower(c); }
27 char operator() (char c) const { return std::toupper(c); }
32 std::string s ("Some Kind Of Initial Input Goes Here");
34 // Change everything into upper case
35 std::transform (s.begin(), s.end(), s.begin(), ToUpper());
37 // Change everything into lower case
38 std::transform (s.begin(), s.end(), s.begin(), ToLower());
40 // Change everything back into upper case, but store the
41 // result in a different string
42 std::string capital_s;
43 capital_s.resize(s.size());
44 std::transform (s.begin(), s.end(), capital_s.begin(), ToUpper());
47 <span class="emphasis"><em>Note</em></span> that these calls all
48 involve the global C locale through the use of the C functions
49 <code class="code">toupper/tolower</code>. This is absolutely guaranteed to work --
50 but <span class="emphasis"><em>only</em></span> if the string contains <span class="emphasis"><em>only</em></span> characters
51 from the basic source character set, and there are <span class="emphasis"><em>only</em></span>
52 96 of those. Which means that not even all English text can be
53 represented (certain British spellings, proper names, and so forth).
54 So, if all your input forevermore consists of only those 96
55 characters (hahahahahaha), then you're done.
56 </p><p><span class="emphasis"><em>Note</em></span> that the
57 <code class="code">ToUpper</code> and <code class="code">ToLower</code> function objects
58 are needed because <code class="code">toupper</code> and <code class="code">tolower</code>
59 are overloaded names (declared in <code class="code"><cctype></code> and
60 <code class="code"><locale></code>) so the template-arguments for
61 <code class="code">transform<></code> cannot be deduced, as explained in
62 <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2002-11/msg00180.html" target="_top">this
65 At minimum, you can write short wrappers like
66 </p><pre class="programlisting">
69 return std::tolower(c);
70 } </pre><p>The correct method is to use a facet for a particular locale
71 and call its conversion functions. These are discussed more in
72 Chapter 22; the specific part is
73 <a class="ulink" href="../22_locale/howto.html#7" target="_top">Correct Transformations</a>,
74 which shows the final version of this code. (Thanks to James Kanze
75 for assistance and suggestions on all of this.)
76 </p><p>Another common operation is trimming off excess whitespace. Much
77 like transformations, this task is trivial with the use of string's
78 <code class="code">find</code> family. These examples are broken into multiple
79 statements for readability:
80 </p><pre class="programlisting">
81 std::string str (" \t blah blah blah \n ");
83 // trim leading whitespace
84 string::size_type notwhite = str.find_first_not_of(" \t\n");
85 str.erase(0,notwhite);
87 // trim trailing whitespace
88 notwhite = str.find_last_not_of(" \t\n");
89 str.erase(notwhite+1); </pre><p>Obviously, the calls to <code class="code">find</code> could be inserted directly
90 into the calls to <code class="code">erase</code>, in case your compiler does not
91 optimize named temporaries out of existence.
92 </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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