Question

I made a simple test program to play around with C++11 threads.

#include <iostream>
#include <stdlib.h>
#include <thread>
using namespace std;

void tee(int civ)
{
    for(int loop=0; loop<19; loop++, civ++)
    {
        civ = civ%19;
        cout << loop << "\t" << civ << endl;
        this_thread::sleep_for(chrono::milliseconds(300));
    }
}

void koot()
{
    while(true)
    {
        cout << ":) ";
        this_thread::sleep_for(chrono::milliseconds(300));
    }
}

int main(int argc, char *argv[])
{
    thread saie(tee, atoi(argv[1])),
        kamaa(koot);
    saie.join();
    kamaa.join();

    return 0;
}

It works fine as long as I supply command line arguments, but if I don’t, it crashes.
How can this be solved?
I tried checking the argument count, and if they existed, to no avail.

EDIT: I had to add this line:

if(argc < 2) return 1;

Answer 1

It crashes because you are accessing

argv[1]

which would hold a command line argument (other than the program’s name) if there was one. You should check whether argc is greater than 1. Why greater than 1? Because the first command line argument is the name of the program itself. So argc is always greater than 0. And indexing starts at 0. So if argc == 1, only argv[0] is valid.

#include <iostream>
int main(int argc, char* argv[])
{
  // no need to check argc for argv[0]
  std::cout << argc << " " << argv[0] << "\n";
}