Thread: Command Line Arguments

Hey guys/gals,

When using command line arguments how would you handle if there is nothing typed in the command. How do I quit the program if the argument is left blank?


example code:

Code:

int main(int argc, char *argv[])
{

y = 0;

x = atoi(argv[1]); //so here if x is nothing...there is nothing placed for the arg...

while(y<x) //how do I make it so it doesn't go through this loop?
{
//do stuff
}


return 0;

}

You should not blindly start using the second parameter in main (usually called argv).
The first parameter (argc) tells you how many items are in the array.

Check argc before blindly using argv

Code:

x = atoi(argv[1]); //so here if x is nothing...there is nothing placed for the arg...

If there is no argument, then you've got a likely seg fault or access violation as you're dabbling in undefined behavior by accessing an array element that does not exist.

Follow CommonTater's advice and use argc to check for the presence of an argument.

LOL. Now that's the kind of helpful error message that "users" need.
As a programmer, I always say the world would be better off without them pesky users.

Haha. But perhaps just "You suck!" is too general; users need more information. Perhaps

Code:

if(argc < 2)  // No argument given
{
  fputs("There is no argument: you suck!\n", stderr);
  exit(EXIT_FAILURE);
}