NAME
        GetCatalogStr -- get a string from a message catalog. (V38)

   SYNOPSIS
        string = GetCatalogStr(catalog,stringNum,defaultString);
        D0                     A0      D0        A1

        strptr getcatalogstr(struct catalog *,long,strptr);

   FUNCTION
        This function returns a specific string within a message catalog.
        If the catalog parameter is NULL, or the requested message does not
        exist, then defaultString is returned.

   INPUTS
        catalog - a message catalog as obtained from opencatalog(), or null
        stringNum - a message number within the catalog
        defaultString - string to return in case "catalog" is NULL or
                        "stringNum" can't be found

   RESULT
        string - a pointer to a NULL-terminated string. The returned string
                 is READ-ONLY, do NOT modify! This string pointer is valid
                 only as long as the catalog remains open.

   SEE ALSO
        opencatalog(), closecatalog()