Array initialization with non constant expression

[Mefisto]

Hi all,
you know the Stroustrup says:"..you cannot initialize an array with a non constant expression" or something like this.
Well, i'm on a mac and i use XCode to compile my c++ projects.
Can you explain me why the hell i'm able to compile without ANY errors and with the correct output, the following code??

Code: Select all

#include <iostream>

int main()
{
     int size;

     std::cin >> size;
     int array[size];

     array[0] = size;//just to test
     std::cout << array[0];
}


Thanks

[Alvaro]

Some compilers allow arrays with run-time size, but the standard doesn't require them to. Your code won't work in other compilers.

I believe XCode uses gcc under the hood. If that is the case, you can try passing option `-pedantic', which will make it complain about something like this.

[Mefisto]

Yes It uses gcc,
so thanks for your clean and full answer!

[jlou]

Note that it's called a variable length array (VLA) and allowed in C99, which is why gcc allows it as an extension for C++ programs. It's not allowed in standard C++.

[GiovaMaster]

thanks for your specification jlou!