View Full Version : using getopt in C

March 5th, 2007, 12:41 AM
Greetings, I am using the getopt function and I had a question. Is there anyway to easily, not require an argument after the r - example

./webserver -p 5000 -r

rather than

./webserver -p 5000 -r /asd

because it does this to me
[bwhit132@csunix webserver]$ ./webserver -p 5000 -r
./webserver: option requires an argument -- r

I want to allow the option but not have it as a necessity.

this is what im doing with it

void processargs(int argc, char **argv) {
int dirSize = 100;
int next_option;
const char* short_options = "p:r:";
do {
next_option = getopt(argc, argv, short_options);
if (next_option != -1) {
switch (next_option)
case 'p': /* -p -- port option */
port = optarg;
case 'r':

myPath = malloc(dirSize); //allocate because we are copying into a null ptr
while (getcwd(myPath,dirSize) == NULL){ //if the directory has a long name, reallocate size
dirSize *= 2;
myPath = malloc(dirSize);
downPath = optarg;
if (downPath == NULL){
printf("\nHAHAAAAA NULL BOY\n");
} else { printf("\n%s\n",downPath); }
/* Unknown option detected. Print it to standard
output, and exit with exit code zero (normal termination). */
fprintf(stderr, USAGE_STRING);

} while (next_option != -1);

if (port == NULL) {
fprintf(stderr, USAGE_STRING);

Edit: In case you were wondering I was just testing with the whole hahaha null boy thing..

Mr. C.
March 5th, 2007, 01:21 AM
man 3 getopt

optstring is a string containing the legitimate option characters. If
such a character is followed by a colon, the option requires an argu-
ment, so getopt places a pointer to the following text in the same
argv-element, or the text of the following argv-element, in optarg.
Two colons mean an option takes an optional arg; if there is text in
the current argv-element, it is returned in optarg, otherwise optarg is
set to zero. This is a GNU extension. If optstring contains W fol-
lowed by a semicolon, then -W foo is treated as the long option --foo.
(The -W option is reserved by POSIX.2 for implementation extensions.)
This behaviour is a GNU extension, not available with libraries before
GNU libc 2.

March 5th, 2007, 01:29 AM
ohhhh thanks. I was looking at the wrong man page. Thanks for your help