## Tcl8.5.14/Tk8.5.14 Documentation > TkLib > GetUid

### Tcl/Tk Applications | Tcl Commands | Tk Commands | Tcl Library | Tk Library

### NAME

Tk_GetUid, Tk_Uid - convert from string to unique identifier

### SYNOPSIS

#include <tk8.5/tk.h>
Tk_Uid
Tk_GetUid(string)

### ARGUMENTS

char *string (in)
  String for which the corresponding unique identifier is desired.

### DESCRIPTION

Tk_GetUid returns the unique identifier corresponding to string. 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 Tk_GetUid is called twice, once with string a and once with string b, and if a and b have the same string value (strcmp(a, b) == 0), then Tk_GetUid 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 strcmp. In addition, the return value from Tk_GetUid will have the same string value as its argument (strcmp(Tk_GetUid(a), a) == 0).

### KEYWORDS

atom, unique identifier
Copyright © 1995-1997 Roger E. Critchlow Jr. Copyright © 1990 The Regents of the University of California. Copyright © 1994-1996 Sun Microsystems, Inc.