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123 lines
3.0 KiB
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<!-- Created by texi2html 1.56k from cln.texi on 14 January 2000 -->
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<TITLE>CLN, a Class Library for Numbers - 8. Symbolic data types</TITLE>
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Go to the <A HREF="cln_1.html">first</A>, <A HREF="cln_7.html">previous</A>, <A HREF="cln_9.html">next</A>, <A HREF="cln_13.html">last</A> section, <A HREF="cln_toc.html">table of contents</A>.
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<P><HR><P>
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<H1><A NAME="SEC51" HREF="cln_toc.html#TOC51">8. Symbolic data types</A></H1>
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<P>
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CLN implements two symbolic (non-numeric) data types: strings and symbols.
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<H2><A NAME="SEC52" HREF="cln_toc.html#TOC52">8.1 Strings</A></H2>
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<P>
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The class
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<PRE>
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String
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cl_string
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<cl_string.h>
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</PRE>
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<P>
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implements immutable strings.
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<P>
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Strings are constructed through the following constructors:
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<DL COMPACT>
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<DT><CODE>cl_string (const char * s)</CODE>
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<DD>
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Returns an immutable copy of the (zero-terminated) C string <CODE>s</CODE>.
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<DT><CODE>cl_string (const char * ptr, unsigned long len)</CODE>
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<DD>
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Returns an immutable copy of the <CODE>len</CODE> characters at
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<CODE>ptr[0]</CODE>, ..., <CODE>ptr[len-1]</CODE>. NUL characters are allowed.
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</DL>
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<P>
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The following functions are available on strings:
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<DL COMPACT>
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<DT><CODE>operator =</CODE>
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<DD>
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Assignment from <CODE>cl_string</CODE> and <CODE>const char *</CODE>.
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<DT><CODE>s.length()</CODE>
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<DD>
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<DT><CODE>strlen(s)</CODE>
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<DD>
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Returns the length of the string <CODE>s</CODE>.
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<DT><CODE>s[i]</CODE>
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<DD>
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Returns the <CODE>i</CODE>th character of the string <CODE>s</CODE>.
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<CODE>i</CODE> must be in the range <CODE>0 <= i < s.length()</CODE>.
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<DT><CODE>bool equal (const cl_string& s1, const cl_string& s2)</CODE>
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<DD>
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Compares two strings for equality. One of the arguments may also be a
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plain <CODE>const char *</CODE>.
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</DL>
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<H2><A NAME="SEC53" HREF="cln_toc.html#TOC53">8.2 Symbols</A></H2>
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<P>
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Symbols are uniquified strings: all symbols with the same name are shared.
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This means that comparison of two symbols is fast (effectively just a pointer
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comparison), whereas comparison of two strings must in the worst case walk
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both strings until their end.
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Symbols are used, for example, as tags for properties, as names of variables
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in polynomial rings, etc.
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<P>
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Symbols are constructed through the following constructor:
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<DL COMPACT>
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<DT><CODE>cl_symbol (const cl_string& s)</CODE>
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<DD>
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Looks up or creates a new symbol with a given name.
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</DL>
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<P>
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The following operations are available on symbols:
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<DL COMPACT>
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<DT><CODE>cl_string (const cl_symbol& sym)</CODE>
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<DD>
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Conversion to <CODE>cl_string</CODE>: Returns the string which names the symbol
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<CODE>sym</CODE>.
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<DT><CODE>bool equal (const cl_symbol& sym1, const cl_symbol& sym2)</CODE>
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<DD>
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Compares two symbols for equality. This is very fast.
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</DL>
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<P><HR><P>
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Go to the <A HREF="cln_1.html">first</A>, <A HREF="cln_7.html">previous</A>, <A HREF="cln_9.html">next</A>, <A HREF="cln_13.html">last</A> section, <A HREF="cln_toc.html">table of contents</A>.
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