3

I know this queston has been asked multiple times, but still I am unable to figure this out 

#include<stdio.h>
#include<getopt.h>
int ch;
int queue_time=60;
int thread_num=4;
char *scheduling_algo="FCFS";
extern char *optarg;
int port=8080;
int debug_flag,h_flag,l_flag;
int main(int argc,char *argv[])
{
  while ((ch = getopt(argc, argv, "dhlprtns")) != -1)
switch(ch)
{
  case 'd':
    debug_flag=atoi(optarg);        /* print address in output */
    break;
  case 'h':
    h_flag=atoi(optarg);
    break;
  case 'l':
    l_flag=atoi(optarg);; 
    break;
  case 'p':
    port = atoi(optarg);
    break;
case 'r':
    printf("%s",optarg); 
    break;
case 't':
    queue_time = atoi(optarg);
    break;
case 'n':
    thread_num = atoi(optarg);
    break;
case 's':
    scheduling_algo = optarg;
    break;
default:
    printf("nothing was passed");
}

    printf("%d",queue_time);
    printf("%d",debug_flag);
    printf("%d",h_flag);
    printf("%d",l_flag);
}

I am executing my program using the following command

./a.out -d -h -l -t 55

I am getting the core dumped error . I read a few examples on google, but still I am facing this problem. Can anyone please help?

Thomas Dickey
  • 51,086
  • 7
  • 70
  • 105
user2934433
  • 343
  • 1
  • 5
  • 20

2 Answers2

15

You need to read the man page for getopt()

  while ((ch = getopt(argc, argv, "dhlprtns")) != -1)
                                   ^^^^^^^^

This does not correspond to the way you are using the arguments. You want colons ":" after the flags which expect arguments. In your code "d" is not followed by a colon and yet you seem to want an value for it:

  case 'd':
    debug_flag=atoi(optarg);        /* print address in output */
    break;

So what is happening is you are calling atoi(0) and this is seg faulting.

Here's the example from the man page, note how "b" is not followed by a colon while "f" is.

#include <unistd.h>
 int bflag, ch, fd;

 bflag = 0;
 while ((ch = getopt(argc, argv, "bf:")) != -1) {
         switch (ch) {
         case 'b':
                 bflag = 1;
                 break;
         case 'f':
                 if ((fd = open(optarg, O_RDONLY, 0)) < 0) {
                         (void)fprintf(stderr,
                             "myname: %s: %s\n", optarg, strerror(errno));
                         exit(1);
                 }
                 break;
         case '?':
         default:
                 usage();
         }
 }
 argc -= optind;
 argv += optind;
Charlie Burns
  • 6,994
  • 20
  • 29
  • Thanks a lot, the man page was very confusing. Now I got a clear picture. I need to use optarg only for those flags which have colon. – user2934433 Oct 30 '13 at 01:35
1

This may be of use to others: You will also get a segfault if you specify an option letter as both without colon, and with colon eg "dabcd:e" - in this case "d" occurs with and without colon.... and then use that option letter.

It appears getopt and its variants do not check for this conflict and return an error!

MikeW
  • 5,504
  • 1
  • 34
  • 29