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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=" ISO C++ , library " /><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<></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> |
