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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>Case Sensitivity</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="bk01pt05ch13.html" title="Chapter 13. String Classes" /><link rel="prev" href="bk01pt05ch13.html" title="Chapter 13. String Classes" /><link rel="next" href="bk01pt05ch13s03.html" title="Arbitrary Character Types" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Case Sensitivity</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk01pt05ch13.html">Prev</a> </td><th width="60%" align="center">Chapter 13. String Classes</th><td width="20%" align="right"> <a accesskey="n" href="bk01pt05ch13s03.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="strings.string.case"></a>Case Sensitivity</h2></div></div></div><p> |
| </p><p>The well-known-and-if-it-isn't-well-known-it-ought-to-be |
| <a class="ulink" href="http://www.gotw.ca/gotw/" target="_top">Guru of the Week</a> |
| discussions held on Usenet covered this topic in January of 1998. |
| Briefly, the challenge was, “<span class="quote">write a 'ci_string' class which |
| is identical to the standard 'string' class, but is |
| case-insensitive in the same way as the (common but nonstandard) |
| C function stricmp()</span>”. |
| </p><pre class="programlisting"> |
| ci_string s( "AbCdE" ); |
| |
| // case insensitive |
| assert( s == "abcde" ); |
| assert( s == "ABCDE" ); |
| |
| // still case-preserving, of course |
| assert( strcmp( s.c_str(), "AbCdE" ) == 0 ); |
| assert( strcmp( s.c_str(), "abcde" ) != 0 ); </pre><p>The solution is surprisingly easy. The original answer was |
| posted on Usenet, and a revised version appears in Herb Sutter's |
| book <span class="emphasis"><em>Exceptional C++</em></span> and on his website as <a class="ulink" href="http://www.gotw.ca/gotw/029.htm" target="_top">GotW 29</a>. |
| </p><p>See? Told you it was easy!</p><p> |
| <span class="emphasis"><em>Added June 2000:</em></span> The May 2000 issue of C++ |
| Report contains a fascinating <a class="ulink" href="http://lafstern.org/matt/col2_new.pdf" target="_top"> article</a> by |
| Matt Austern (yes, <span class="emphasis"><em>the</em></span> Matt Austern) on why |
| case-insensitive comparisons are not as easy as they seem, and |
| why creating a class is the <span class="emphasis"><em>wrong</em></span> way to go |
| about it in production code. (The GotW answer mentions one of |
| the principle difficulties; his article mentions more.) |
| </p><p>Basically, this is "easy" only if you ignore some things, |
| things which may be too important to your program to ignore. (I chose |
| to ignore them when originally writing this entry, and am surprised |
| that nobody ever called me on it...) The GotW question and answer |
| remain useful instructional tools, however. |
| </p><p><span class="emphasis"><em>Added September 2000:</em></span> James Kanze provided a link to a |
| <a class="ulink" href="http://www.unicode.org/unicode/reports/tr21/" target="_top">Unicode |
| Technical Report discussing case handling</a>, which provides some |
| very good information. |
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