VMS Help RTL Routines, LIB$, LIB$MOVTUC, Returns  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

    The relative position in the source string of the character that
    is translated to the stop character. Zero is returned if the stop
    character is not found. This value is set to -1 if destination-
    string cannot be allocated.