Tcl_GetIndexFromObj(3) Tcl Library Procedures Tcl_GetIndexFromObj(3)______________________________________________________________________________NAME
Tcl_GetIndexFromObj, Tcl_GetIndexFromObjStruct - lookup string in table
of keywords
SYNOPSIS
#include <tcl.h>
int
Tcl_GetIndexFromObj(interp, objPtr, tablePtr, msg, flags,
indexPtr)
int
Tcl_GetIndexFromObjStruct(interp, objPtr, structTablePtr, offset,
msg, flags, indexPtr)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter to use for error
reporting; if NULL, then no
message is provided on errors.
Tcl_Obj *objPtr (in/out) The string value of this
object is used to search
through tablePtr. The inter‐
nal representation is modified
to hold the index of the
matching table entry.
const char **tablePtr (in) An array of null-terminated
strings. The end of the array
is marked by a NULL string
pointer. Note that references
to the tablePtr may be
retained in the internal rep‐
resentation of objPtr, so this
should represent the address
of a statically-allocated
array.
const void *structTablePtr (in) An array of arbitrary type,
typically some struct type.
The first member of the struc‐
ture must be a null-terminated
string. The size of the
structure is given by offset.
Note that references to the
structTablePtr may be retained
in the internal representation
of objPtr, so this should rep‐
resent the address of a stati‐
cally-allocated array of
structures.
int offset (in) The offset to add to struct‐
TablePtr to get to the next
entry. The end of the array
is marked by a NULL string
pointer.
const char *msg (in) Null-terminated string
describing what is being
looked up, such as option.
This string is included in
error messages.
int flags (in) OR-ed combination of bits pro‐
viding additional information
for operation. The only bit
that is currently defined is
TCL_EXACT.
int *indexPtr (out) The index of the string in
tablePtr that matches the
value of objPtr is returned
here.
_________________________________________________________________DESCRIPTION
These procedures provide 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. Tcl_GetIndexFromObj
compares objPtr against each of the strings in tablePtr to find a
match. A match occurs if objPtr's string value is identical to one of
the strings in tablePtr, or if it is a non-empty unique abbreviation
for exactly one of the strings in tablePtr and the TCL_EXACT flag was
not specified; in either case the index of the matching entry is stored
at *indexPtr and TCL_OK is returned.
If there is no matching entry, TCL_ERROR is returned and an error mes‐
sage is left in interp's result if interp is not NULL. Msg is included
in the error message to indicate what was being looked up. For exam‐
ple, if msg is option the error message will have a form like “bad
option "firt": must be first, second, or third”.
If Tcl_GetIndexFromObj completes successfully it modifies the internal
representation of objPtr to hold the address of the table and the index
of the matching entry. If Tcl_GetIndexFromObj is invoked again with
the same objPtr and tablePtr arguments (e.g. during a reinvocation of a
Tcl command), it returns the matching index immediately without having
to redo the lookup operation. Note: Tcl_GetIndexFromObj assumes that
the entries in tablePtr are static: they must not change between invo‐
cations. If the value of objPtr is the empty string, Tcl_GetIndexFro‐
mObj will treat it as a non-matching value and return TCL_ERROR.
Tcl_GetIndexFromObjStruct works just like Tcl_GetIndexFromObj, except
that instead of treating tablePtr as an array of string pointers, it
treats it as a pointer to the first string in a series of strings that
have offset bytes between them (i.e. that there is a pointer to the
first array of characters at tablePtr, a pointer to the second array of
characters at tablePtr+offset bytes, etc.) This is particularly useful
when processing things like Tk_ConfigurationSpec, whose string keys are
in the same place in each of several array elements.
SEE ALSO
Tcl_WrongNumArgs
KEYWORDS
index, object, table lookup
Tcl 8.1 Tcl_GetIndexFromObj(3)
