path: root/doc/GetIndex.3

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'\" Copyright (c) 1997 Sun Microsystems, Inc.
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'\" RCS: @(#) $Id: GetIndex.3,v 1.22 2007/12/13 15:22:31 dgp Exp $
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.so man.macros
.TH Tcl_GetIndexFromObj 3 8.1 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_GetIndexFromObj, Tcl_GetIndexFromObjStruct \- lookup string in table of keywords
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
int
\fBTcl_GetIndexFromObj\fR(\fIinterp, objPtr, tablePtr, msg, flags,
indexPtr\fR)
.sp
int
\fBTcl_GetIndexFromObjStruct\fR(\fIinterp, objPtr, structTablePtr, offset,
                          msg, flags, indexPtr\fR)
.SH ARGUMENTS
.AS "const char" *structTablePtr in/out
.AP Tcl_Interp *interp in
Interpreter to use for error reporting; if NULL, then no message is
provided on errors.
.AP Tcl_Obj *objPtr in/out
The string value of this object is used to search through \fItablePtr\fR.
The internal representation is modified to hold the index of the matching
table entry.
.AP "const char" **tablePtr in
An array of null-terminated strings.  The end of the array is marked
by a NULL string pointer.
.AP "const void" *structTablePtr in
An array of arbitrary type, typically some \fBstruct\fR type.
The first member of the structure must be a null-terminated string.
The size of the structure is given by \fIoffset\fR.
.AP int offset in
The offset to add to structTablePtr to get to the next entry.
The end of the array is marked by a NULL string pointer.
.AP "const char" *msg in
Null-terminated string describing what is being looked up, such as
\fBoption\fR.  This string is included in error messages.
.AP int flags in
OR-ed combination of bits providing additional information for
operation.  The only bit that is currently defined is \fBTCL_EXACT\fR.
.AP int *indexPtr out
The index of the string in \fItablePtr\fR that matches the value of
\fIobjPtr\fR is returned here.
.BE

.SH DESCRIPTION
.PP
This procedure provides an efficient way for looking up keywords,
switch names, option names, and similar things where the value of
an object must be one of a predefined set of values.
\fIObjPtr\fR is compared against each of
the strings in \fItablePtr\fR to find a match.  A match occurs if
\fIobjPtr\fR's string value is identical to one of the strings in
\fItablePtr\fR, or if it is a non-empty unique abbreviation
for exactly one of the strings in \fItablePtr\fR and the
\fBTCL_EXACT\fR flag was not specified; in either case
the index of the matching entry is stored at \fI*indexPtr\fR
and \fBTCL_OK\fR is returned.
.PP
If there is no matching entry,
\fBTCL_ERROR\fR is returned and an error message is left in \fIinterp\fR's
result if \fIinterp\fR is not NULL.  \fIMsg\fR is included in the
error message to indicate what was being looked up.  For example,
if \fImsg\fR is \fBoption\fR the error message will have a form like
.QW "\fBbad option \N'34'firt\N'34': must be first, second, or third\fR" .
.PP
If \fBTcl_GetIndexFromObj\fR completes successfully it modifies the
internal representation of \fIobjPtr\fR to hold the address of
the table and the index of the matching entry.  If \fBTcl_GetIndexFromObj\fR
is invoked again with the same \fIobjPtr\fR and \fItablePtr\fR
arguments (e.g. during a reinvocation of a Tcl command), it returns
the matching index immediately without having to redo the lookup
operation.  Note: \fBTcl_GetIndexFromObj\fR assumes that the entries
in \fItablePtr\fR are static: they must not change between
invocations.  If the value of \fIobjPtr\fR is the empty string,
\fBTcl_GetIndexFromObj\fR will treat it as a non-matching value
and return \fBTCL_ERROR\fR.
.PP
\fBTcl_GetIndexFromObjStruct\fR works just like
\fBTcl_GetIndexFromObj\fR, except that instead of treating
\fItablePtr\fR as an array of string pointers, it treats it as a
pointer to the first string in a series of strings that have
\fIoffset\fR bytes between them (i.e. that there is a pointer to the
first array of characters at \fItablePtr\fR, a pointer to the second
array of characters at \fItablePtr\fR+\fIoffset\fR bytes, etc.)
This is particularly useful when processing things like
\fBTk_ConfigurationSpec\fR, whose string keys are in the same place in
each of several array elements.

.SH "SEE ALSO"
Tcl_WrongNumArgs

.SH KEYWORDS
index, object, table lookup