Non-const declaration of array

Question

I have been teaching myself programming for couple of years, and I was sure that if you need array declaration of a variable number you need to use malloc or new.

Today I found that this compiles under g++ version 4.4.4, without warnings or errors:

#include <iostream>
using namespace std;

int main()
{
    int size_array;
    cin >> size_array;
    int iTable[size_array];

    for(int i=0;i < size_array;i++)
        iTable[i]=i*i;
    for(int i=0;i < size_array;i++)
        cout << iTable[i] << endl;

    return 0;
}

Also it compiles completely fine if you are using gcc (after changing cout and cin with printf and scanf)

Under Visual Studio this code fails to compile since size_array is not constant.

When this was changed? This is a safe method?

Answer 1

This is a C99 feature - VLA - which is not a part of standard c++. You can use it if your compiler supports it and you don't require portability. If the compiler supports it, it's perfectly safe to use - but it's a bad habit using non-standard features.

Answer 2

This is a compiler extension of gcc, not standard.

Answer 3

No thats not safe at all. It could corrupt your stack.