source-string

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

    String that STR$FIND_FIRST_SUBSTRING searches. The source-string
    argument is the address of a descriptor pointing to the string.

 index

    OpenVMS usage:longword_signed
    type:         longword (signed)
    access:       write only
    mechanism:    by reference

    Earliest position within source-string at which STR$FIND_FIRST_
    SUBSTRING found a matching substring; zero if no matching
    substring was found. The index argument is the address of a
    signed longword containing this position.

 substring-index

    OpenVMS usage:longword_signed
    type:         longword (signed)
    access:       write only
    mechanism:    by reference

    Ordinal number of the substring that matched (1 for the first, 2
    for the second, and so on), or zero if STR$FIND_FIRST_SUBSTRING
    found no substrings that matched. The substring-index argument is
    the address of a signed longword containing this ordinal number.

 substring

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

    Specified substring for which STR$FIND_FIRST_SUBSTRING searches
    in source-string. The substring argument is the address of a
    descriptor pointing to the first substring. You can specify
    multiple substrings to search for.

 substring

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

    Additional specified substring for which STR$FIND_FIRST_SUBSTRING
    searches in source-string. The substring argument is the address
    of a descriptor pointing to the substring. You can specify
    multiple substrings to search for.