archie/tk4.2/doc/GetUid.3

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'\" Copyright (c) 1990 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\" SCCS: @(#) GetUid.3 1.10 96/03/26 18:12:55
'\" 
.so man.macros
.TH Tk_GetUid 3 "" Tk "Tk Library Procedures"
.BS
.SH NAME
Tk_GetUid, Tk_Uid \- convert from string to unique identifier
.SH SYNOPSIS
.nf
\fB#include <tk.h>\fR
.sp
\fB#typedef char *Tk_Uid\fR
.sp
Tk_Uid
\fBTk_GetUid\fR(\fIstring\fR)
.SH ARGUMENTS
.AP char *string in
String for which the corresponding unique identifier is
desired.
.BE

.SH DESCRIPTION
.PP
\fBTk_GetUid\fR returns the unique identifier corresponding
to \fIstring\fR.
Unique identifiers are similar to atoms in Lisp, and are used
in Tk to speed up comparisons and
searches.  A unique identifier (type Tk_Uid) is a string pointer
and may be used anywhere that a variable of type ``char *''
could be used.  However, there is guaranteed to be exactly
one unique identifier for any given string value.  If \fBTk_GetUid\fR
is called twice, once with string \fIa\fR and once with string
\fIb\fR, and if \fIa\fR and \fIb\fR have the same string value
(strcmp(a, b) == 0), then \fBTk_GetUid\fR will return exactly
the same Tk_Uid value for each call (Tk_GetUid(a) == Tk_GetUid(b)).
This means that variables of type
Tk_Uid may be compared directly (x == y) without having to call
\fBstrcmp\fR.
In addition, the return value from \fBTk_GetUid\fR will have the
same string value as its argument (strcmp(Tk_GetUid(a), a) == 0).

.SH KEYWORDS
atom, unique identifier