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.
_________________________________________________________________

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(3tcl), Tcl_WrongNumArgs(3tcl)

KEYWORDS

       index, option, value, table lookup