The Find First Substring in Input String routine finds the first
    substring (in a provided list of substrings) occurring in a given
    string.

    Format

      STR$FIND_FIRST_SUBSTRING  source-string ,index ,substring-index

                                ,substring [,substring...]

1  –  Returns

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

    The values returned by STR$FIND_FIRST_SUBSTRING and the
    conditions to which they translate are as follows:

    Returned
    Value          Condition

    0              source-string did not contain any of the specified
                   substrings.
    1              STR$FIND_FIRST_SUBSTRING found at least one of the
                   specified substrings in source-string.

2  –  Arguments

 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.