How to read program arguments [closed]

Answer 1

int main(int argc, int **argv)

Using arguments of main, you should know the first argument argv[0] is the name of current executing file, and the following arguments are the parameters sent to your program.

In your case, you must read argv[1].

Always check argc to count the entered arguments.

Answer 2

This has nothing to do with threads per se.

The first argument to your program, if given, will be found in argv[1] but as a string, so you need to turn it into an integer with something like atoi or strtol.

Answer 3

Here is a minimal example with complete, correct error checking and diagnostic messages. Note that setting errno to 0 is necessary for distinguishing range errors from valid strtoul() outputs, this is an annoying quirk of the function.

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
int main(int argc, char *argv[])
{
    if (argc != 2) {
        fputs("usage: test NTHREAD\n", stderr);
        exit(1);
    }
    char *e;
    errno = 0;
    unsigned long nthread = strtoul(argv[1], &e, 0);
    if (!*argv[1] || *e) {
        fputs("error: invalid NTHREAD\n", stderr);
        exit(1);
    }
    if (nthread == (unsigned long) -1 && errno == ERANGE) {
        fputs("error: NTHREAD out of range\n", stderr);
        exit(1);
    }
    // Your code goes here
}