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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 V1.73.2" /><meta name="keywords" content="&#10;      ISO C++&#10;    , &#10;      library&#10;    " /><link rel="start" 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&lt;&gt;</code> is used.
   </p><p>
     This code will go through some iterations.  Here's a simple
     version:
   </p><pre class="programlisting">
   #include &lt;string&gt;
   #include &lt;algorithm&gt;
   #include &lt;cctype&gt;      // old &lt;ctype.h&gt;

   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">&lt;cctype&gt;</code> and
      <code class="code">&lt;locale&gt;</code>) so the template-arguments for
      <code class="code">transform&lt;&gt;</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>