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Tcl_GetIndexFromObj(3) Tcl Library Procedures Tcl_GetIndexFromObj(3)
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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 value
is used to search through
tablePtr. The internal
representation is modified to
hold the index of the matching
table entry.
const char *const *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
representation 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
structure 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 represent the
address of a statically-
allocated array of structures.
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.
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
providing 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.
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DESCRIPTION
These procedures provide an efficient way for looking up keywords,
switch names, option names, and similar things where the literal value
of a Tcl value must be chosen from a predefined set.
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
message 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 example, 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
invocations. If the value of objPtr is the empty string,
Tcl_GetIndexFromObj 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
prefix(n), Tcl_WrongNumArgs(3)
KEYWORDS
index, option, value, table lookup
Tcl 8.1 Tcl_GetIndexFromObj(3)