Thread: Quick input check question

So I want to check to see if the command line argument I received was an integer. How do I do this?

Code:

#include <iostream>
using namespace std;

int main(int argc, char* argv[]) {
	//**************************
	//Checking for correct input
	//**************************

	if ( argc != 2 ) {
		cerr << "Usage: " << argv[0] << " n" << endl;
		return 1;
    }

	if ( argv[1].isdigit() != 1 && ) {
		cerr << "Usage: n must be a positive integer." << endl;
		return 1;
	}
}

However, the error message says that there is a request for member isdigit in *(argv + 4u) which is of nonclass type char*.

I don't really understand the error message.

isdigit is not a member function of anything, it's just a function. It also only works on a char, not a char*. The C way would be to use strtol (also not a member function) and pay attention to the second pointer argument to make sure it's at the end of the string. I don't know that there's much better in C++; boost's lexical_cast, maybe.

Yes, thanks, I'm an idiot. (I'm pretty sure I've suggested that before, too; don't know why it didn't come to mind this time.)