F.GCAT - return the named substructure block.

Usage:

substruct = f.gcat( cat_blk, sub_name
                [, owner, permptr, who ] )

Where:

cat_blk: is the memory address of a type 0 or 1 catalog block describing the current catalog level. The named substructure will be found if it is contained on this block, or on any subsequent block in the chain of type 1 blocks.
sub_name: is the pointer to the two-word BCD name of the desired substructure.
owner: is a pointer to the two-word BCD userid of the owner of the catalog structure being searched. This is only needed if the substructure is located on a removable pack, and the PMC must be searched. If this value is not provided or is zero, it defaults to "&.uid".
permptr: is a pointer to a word containing permissions accumulated up to the catalog level being searched. This word is in the format described in "expl b syslib f.init". The new permissions are returned through this pointer. If this argument is missing or is zero, no permission checking is done.
who: is the userid to be used when checking permissions. If this is not supplied or is 0, the value "&.uid" is used.
substruct: is the memory address of the substructure's type 0 or type 2 catalog block.

Description:

F.GCAT is used to run down a catalog structure, optionally checking permissions. The current catalog level is searched, starting at the given type 0 or type 1 block, until the named structure is found or the chain to type 1 blocks is exhausted.

The original catalog block is not busied, and may be overwritten by a call to this function.

If the substructure is not found or resides on an unmounted removable pack, the negative of the appropriate FMS status is returned.