Question

I need to learn C++ basics for a research project, and I’m experimenting with error/exception handling. I did use the throw command successfully to anticipate on events that might occur (like divide by zero), but I cannot figure out how to catch unanticipated exceptions. Take this example code:

#include <iostream>
#include <exception>
#include <stdexcept>
using namespace std;

void arrayOutOfBound()
{
    int a[3] = {1, 2, 3};

    try
    {
        cout << "This should not display: " << a[5] << endl;
    }
    catch(runtime_error &e)
    /* catch(exception &e)     // also does not work  */
    {
        cout << "Error: " << e.what() << endl;
    }
}

int main()
{
    arrayOutOfBound();
}

I guess I have to use throw statements somewhere, but suppose I really did not know that a[5] wouldn’t work (or the user entered this index and I did not check for the array size), then how can I prevent the program from crashing? (as this happens in the Visual C++ Express 2010 debugger)

Note: if I would do try { int result = a[5]; } first, outside the block, and try to use cout << result at the end, the program does not compile. The compiler is trying to help me, but therefore I cannot try the exception handling.

Answer 1

suppose I really did not know that a[5] wouldn’t work (or the user entered this index and I did not check for the array size), then how can I prevent the program from crashing?

You simply can’t. An out of bounds access to an array causes undefined behavior in C++, it won’t throw an exception. When you are lucky enough, you get a crash.