C ++ EXC_BAD_ACCESS，argv []

Question

I've been stuck on this for a while and can't debug this EXC_BAD_ACCESS error. I have run NSZombie and I am pretty sure its a memory issue with argv[1] (or anything more for that matter). I've checked my syntax and libraries so I don't know why it wont store past arg[0] .

#include <iostream>
#include <cstdlib>
#include <cstring>
using namespace std;

int main(int argc, char* argv[])
{
    cout << "Enter the initial bankroll" << endl;
    int bankroll = atoi(argv[1]); //code faults here

    cout << "Enter seed" << endl;
    int seed = atoi(argv[2]);

    // ...

I left out the rest because the error occurs before anything else.

The code runs in the terminal but fails the automatic grader for my class.

Arguments entered:

./blackjack 400 1

Should work for any numbers.

Shouldn't argv[0] would be blackjack, argv[1] the first number and argv[2] the second?

Answer 1

cout doesn't fill the elements of argv , those come from the command line used to execute your program. Also, whenever you use argv , be sure to check argc , which is the number of valid indices into argv . Your program is probably crashing because you haven't passed any arguments to your program, and so the elements of argv aren't usable.

You'll need to use cin calls to read the user input that you're expecting, or change your program to use values passed in from the command line, ie no prompts or reads.

Your added assumptions are correct about argv : if you execute the program with: ./blackjack 400 1 , then argv[1] should be 400 , and argv[2] should be 1 .

Since, based on your edit, you seem to want to get these numbers from the command-line, then remove your cout calls.

Answer 2

As others have noted argv are command line arguments. If they are filled you just use them. I often do like this:

int
main(int n_app_args, char** app_arg)
{
  std::string nec_file;
  if (n_app_args > 1)
    nec_file = app_arg[1];
  else
  {
    std::cout << "Enter NEC output file: ";
    std::cin >> nec_file;
  }

where if I forget the command line argument the program asks me. If I remember the argument the argument is used without further intervention. You can obviously extend this to more arguments.