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)