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158 lines
8.2 KiB
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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN">
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<!Converted with LaTeX2HTML 0.6.5 (Tue Nov 15 1994) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds >
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<HEAD>
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<TITLE>18.2. String Comparison</TITLE>
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<BODY>
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<meta name="description" value=" String Comparison">
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<meta name="keywords" value="clm">
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<meta name="resource-type" value="document">
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<meta name="distribution" value="global">
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<P>
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<b>Common Lisp the Language, 2nd Edition</b>
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<BR> <HR><A NAME=tex2html3598 HREF="node167.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html3596 HREF="node164.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html3590 HREF="node165.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html3600 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html3601 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html3599 HREF="node167.html"> String Construction and </A>
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<B>Up:</B> <A NAME=tex2html3597 HREF="node164.html"> Strings</A>
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<B> Previous:</B> <A NAME=tex2html3591 HREF="node165.html"> String Access</A>
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<HR> <P>
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<H1><A NAME=SECTION002220000000000000000>18.2. String Comparison</A></H1>
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<P>
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The naming conventions for these functions and for their keyword
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arguments generally follow the conventions for the generic sequence
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functions (see chapter <A HREF="node141.html#KSEQUE">14</A>).
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<p>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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Note that this remark, predating the design of the Common Lisp Object System,
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uses the term ``generic'' in a generic sense and not necessarily
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in the technical sense used by CLOS
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(see chapter <A HREF="node15.html#DTYPES">2</A>).
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<BR><b>[Function]</b><BR>
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<tt>string= <i>string1</i> <i>string2</i> &key :start1 :end1 :start2 :end2</tt><P><tt>string=</tt> compares two strings and is true if
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they are the same (corresponding characters are identical)
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but is false if they are not.
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The function <tt>equal</tt> calls <tt>string=</tt> if
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applied to two strings.
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<P>
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The keyword arguments <tt>:start1</tt> and <tt>:start2</tt> are the places
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in the strings to start the comparison.
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The arguments <tt>:end1</tt> and <tt>:end2</tt> are the
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places in the strings to stop comparing; comparison stops just
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<i>before</i> the position specified by a limit.
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The ``start'' arguments default to zero (beginning of string),
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and the ``end'' arguments (if either omitted or <tt>nil</tt>)
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default to the lengths of the strings (end of string),
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so that by default the entirety of each string is examined.
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These arguments are provided so that substrings can be compared
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efficiently.
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<P>
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<tt>string=</tt> is necessarily false if the (sub)strings
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being compared are of unequal length; that is, if
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<P><pre>
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(not (= (- end1 start1) (- end2 start2)))
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</pre><P>
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is true, then <tt>string=</tt> is false.
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<P>
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<P><pre>
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(string= "foo" "foo") is true
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(string= "foo" "Foo") is false
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(string= "foo" "bar") is false
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(string= "together" "frog" :start1 1 :end1 3 :start2 2)
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is true
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</pre><P>
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<P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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X3J13 voted in June 1989 (STRING-COERCION) <A NAME=18203> </A>
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to clarify string coercion (see <tt>string</tt>).
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<hr>
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<b>Compatibility note:</b> <tt>string=</tt> is called <tt>strequal</tt> in Interlisp.
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<hr>
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<P>
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<BR><b>[Function]</b><BR>
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<tt>string-equal <i>string1</i> <i>string2</i> &key :start1 :end1 :start2 :end2</tt><P><tt>string-equal</tt> is just like <tt>string=</tt> except that differences
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in case are ignored; two characters are considered to be the same
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if <tt>char-equal</tt> is true of them.
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For example:
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<P><pre>
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(string-equal "foo" "Foo") is true
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</pre><P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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X3J13 voted in June 1989 (STRING-COERCION) <A NAME=18219> </A>
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to clarify string coercion (see <tt>string</tt>).
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<BR><b>[Function]</b><BR>
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<pre>
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string< <i>string1</i> <i>string2</i> &key :start1 :end1 :start2 :end2
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string> <i>string1</i> <i>string2</i> &key :start1 :end1 :start2 :end2
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string<= <i>string1</i> <i>string2</i> &key :start1 :end1 :start2 :end2
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string>= <i>string1</i> <i>string2</i> &key :start1 :end1 :start2 :end2
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string/= <i>string1</i> <i>string2</i> &key :start1 :end1 :start2 :end2
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</pre>
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<P>These functions compare the two string arguments lexicographically,
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and the result is <tt>nil</tt> unless <i>string1</i> is respectively
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less than, greater than,
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less than or equal to, greater than or equal to, or not equal to <i>string2</i>.
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If the condition is satisfied, however, then
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the result is the index within the strings of the first character
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position at which the strings fail to match; put another way,
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the result is the length of the longest common prefix of the strings.
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<P>
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A string <i>a</i> is less than a string <i>b</i> if
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in the first position in which they differ the character of <i>a</i>
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is less than the corresponding character of <i>b</i> according to
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the function <tt>char<</tt>, or
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if string <i>a</i> is a proper prefix of string <i>b</i>
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(of shorter length and matching in all the characters of <i>a</i>).
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<P>
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The keyword arguments <tt>:start1</tt> and <tt>:start2</tt> are the places
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in the strings to start the comparison.
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The keyword arguments <tt>:end1</tt> and <tt>:end2</tt>
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are the places in the strings to stop comparing; comparison stops just
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<i>before</i> the position specified by a limit.
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The ``start'' arguments default to zero (beginning of string),
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and the ``end'' arguments (if either omitted or <tt>nil</tt>)
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default to the lengths of the strings (end of string),
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so that by default the entirety of each string is examined.
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These arguments are provided so that substrings can be compared
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efficiently. The index returned in case of a mismatch
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is an index into <i>string1</i>.
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<P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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X3J13 voted in June 1989 (STRING-COERCION) <A NAME=18243> </A>
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to clarify string coercion (see <tt>string</tt>).
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<BR><b>[Function]</b><BR>
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<pre>
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string-lessp <i>string1</i> <i>string2</i> &key :start1 :end1 :start2 :end2
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string-greaterp <i>string1</i> <i>string2</i> &key :start1 :end1 :start2 :end2
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string-not-greaterp <i>string1</i> <i>string2</i> &key :start1 :end1 :start2 :end2
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string-not-lessp <i>string1</i> <i>string2</i> &key :start1 :end1 :start2 :end2
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string-not-equal <i>string1</i> <i>string2</i> &key :start1 :end1 :start2 :end2
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</pre>
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<P>These are exactly like <tt>string<</tt>, <tt>string></tt>, <tt>string<=</tt>,
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<tt>string>=</tt>, and <tt>string/=</tt>, respectively, except that distinctions between
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uppercase and lowercase letters are ignored. It is as if
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<tt>char-lessp</tt> were used instead of <tt>char<</tt>
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for comparing characters.
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<P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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X3J13 voted in June 1989 (STRING-COERCION) <A NAME=18256> </A>
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to clarify string coercion (see <tt>string</tt>).
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<BR> <HR><A NAME=tex2html3598 HREF="node167.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html3596 HREF="node164.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html3590 HREF="node165.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html3600 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html3601 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html3599 HREF="node167.html"> String Construction and </A>
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<B>Up:</B> <A NAME=tex2html3597 HREF="node164.html"> Strings</A>
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<B> Previous:</B> <A NAME=tex2html3591 HREF="node165.html"> String Access</A>
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<HR> <P>
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<HR>
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<P><ADDRESS>
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AI.Repository@cs.cmu.edu
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</ADDRESS>
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</BODY>
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