Differences to C's getopt() & getopt_long()

Differences oft f90getoptto the C-functions getopt() and getopt_long().

From C version

• when options are finished, C version returns -1 instead of char(0), and thus stupidly requires an int instead of a char.
• does not support optreset
• does not support "--" as last argument
• if no argument, optarg is blank, not NULL
• argc and argv are implicit

For long options

• optional argument to getopt(), rather than separate function getopt_long()
• has_arg is logical, and does not support optional_argument
• does not support flag field (and thus always returns val)
• does not support longindex
• knows the length of longopts, so does not need an empty last record