Segmentation fault - Core Dumped error while using getopt - c++

Question

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?

Answer 1

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;

Answer 2

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!