Array with size 0 [duplicate]

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.

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

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

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.