getopt adding extra functionality in C - c

Question

here is my question. I want to be able to support this in my application:
./cipher [-devh] [-p PASSWD] infile outfile
I managed to get the [-devh] supported, but I don't know how to get [-p PASSWORD] supported. Of course I can manually check for argc being 2 and then have a bunch of flags but I prefer using getopts and think it would be easier. Here is my code for the [-devh] how can I extend it so it can support them remaining?
while ( (c = getopt(argc, argv, "devh")) != -1) {
switch (c) {
case 'd':
printf ("option d\n");
dopt = 1;
break;
case 'e':
printf ("option e\n");
eopt = 1;
break;
case 'v':
printf ("option v\n");
vopt = 1;
break;
case 'h':
printf ("option h\n");
hopt = 1;
break;
default:
printf ("?? getopt returned character code 0%o ??\n", c);
}
}

Answer 1

Taken directly from the GNU C Library Reference page on getopt:
while ((c = getopt (argc, argv, "abc:")) != -1)
switch (c)
{
case 'a':
aflag = 1;
break;
case 'b':
bflag = 1;
break;
case 'c':
cvalue = optarg;
break;
case '?':
if (optopt == 'c')
fprintf (stderr, "Option -%c requires an argument.\n", optopt);
else if (isprint (optopt))
fprintf (stderr, "Unknown option `-%c'.\n", optopt);
else
fprintf (stderr, "Unknown option character `\\x%x'.\n", optopt);
return 1;
default:
abort();
}
c here is the argument that takes an optional parameter, so this is probably the syntax you were looking for.
What I understand getopt does is loop through the given arguments, parsing them one at a time. So when it gets to the option c (in your case p) where a second argument is required, it is stored in optarg. This is assigned to a variable of your choice (here cvalue) for later processing.