The Index to Relative Position of Substring routine returns an
    index, which is the relative position of the first occurrence of
    a substring in the source string.

    Format

      LIB$INDEX  source-string ,sub-string

1 - Returns

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

    The relative position of the first character of the substring if
    found, or zero if not found.

    On Alpha and I64 systems, if the relative position of the
    substring can exceed 2**32-1, assign the return value to a
    quadword to ensure that you retrieve the correct relative
    position.

2 - Arguments

 source-string

    OpenVMS usage:char_string
    type:         character string
    access:       read only
    mechanism:    by descriptor

    Source string to be searched by LIB$INDEX. The source-string
    argument is the address of a descriptor pointing to this source
    string.

 sub-string

    OpenVMS usage:char_string
    type:         character string
    access:       read only
    mechanism:    by descriptor

    Substring to be found. The sub-string argument is the address of
    a descriptor pointing to this substring.