Question

I am passing my program inputs and I could see them in argv but getopt doesnt seem to have the argument that I expect.

This is how I run my prog: ./my_prog -X -f filename

<snip>
while ((opt = getopt(argc, argv, "Xf:eE:dD")) != EOF) {
    switch (opt) {
       case 'X':
       case 'f':
                if (optarg == NULL)
                fput("no point of living", fp);         << for debugging

</snip>

I always get optarg as null. WHY?

Answer 1

Your argument string does not have a : after the X (e.g. X:f) so optarg will always be null.

I’ll also point out that generally in a switch statement you’ll want a break after each case (generally, not always, but when parsing arguments usually), so:

switch ( ... ) {
    case 'X': {
        // do something
    } break;

    case 'f': {
        // do something else
    } break;
}