Array with size 0

Question

Today I incidentally defined a two dimensional array with the size of one dimension being 0, however my compiler did not complain. I found the following which states that th

Answer 1

Your link explains everything. They are used as last field in a struct when the length of struct is not known at compile time. If you try using them on stack or in a middle of other declarations you will end up overwriting next elements.

Answer 2

In C++ it is illegal to declare an array of zero length. As such it is not normally considered a good practice as you are tying your code to a particular compiler extension. Many uses of dynamically sized arrays are better replaced with a container class such as std::vector.

ISO/IEC 14882:2003 8.3.4/1:

If the constant-expression (5.19) is present, it shall be an integral constant expression and its value shall be greater than zero.

However, you can dynamically allocate an array of zero length with new[].

ISO/IEC 14882:2003 5.3.4/6:

The expression in a direct-new-declarator shall have integral or enumeration type (3.9.1) with a non-negative value.

Answer 3

Compiling your example with gcc, all three of them have sizeof 0, so I would assume that all of them are treated equally by the compiler.

Answer 4

I ran this program at ideone.com

#include <iostream>

int main()
{
    int a[0];
    int b[0][100];
    int c[100][0];

    std::cout << "sizeof(a) = " << sizeof(a) << std::endl;
    std::cout << "sizeof(b) = " << sizeof(b) << std::endl;
    std::cout << "sizeof(c) = " << sizeof(c) << std::endl;

    return 0;
}

It gave the size of all the variables as 0.

sizeof(a) = 0
sizeof(b) = 0
sizeof(c) = 0

So in the above example, no memory is allocated for a, b or c.