Which compilers support arrays with a size fixed at runtime and which compilers don't?

Question

I've been always using arrays whose size are asked in the input by the user like:

int main(){
    int n;
    cin>>n;
    int arr[n];
}

I never faced any problem with this method but now I've read a lot of articles saying that this syntax is not supported by C++ as C++ needs array size at compile time or arrays must be made dynamically using new keyword. Could anybody make this clear if the above code:

Is supported by new compilers and not by the old compilers. If yes, then after which version this syntax is supported?
Allocates the array dynamically in Heap or is this static memory allocation in stack?

using std::vector is a better way to approach arrays. Then you can do resize to make the vector (array) as big as you want, and the memory is managed for you. — ttemple, Jul 23 '20 at 13:07
Why do you wonder? What is the actual problem you're trying to solve? Why can't you use `std::vector` which is the standard way of handling run-time sized "arrays"? — Some programmer dude, Jul 23 '20 at 13:10
Microsoft's Visual C++ compiler does not and probably never will support variable-length arrays (unless the C++ standard will ever require it) — UnholySheep, Jul 23 '20 at 13:13
Go to https://gcc.godbolt.org/ and check the compilers you're interested in. — HolyBlackCat, Jul 23 '20 at 13:16
Well, there are the [usual suspects](https://godbolt.org/z/MqdPcd), but isn't it time to start using standard (since decades) containers like `std::vector`? — Bob__, Jul 23 '20 at 13:22
@ttemple @Some Programmer Dude @Bob__ .. Ya vectors might be better in handling these types of situations. In fact, while practicing, I too use vectors but I wanted to get an insight of how this thing actually works. `Abstraction` is good for users, not programmers/developers. — Shashank Gupta, Jul 23 '20 at 13:43
If you want to learn how they work, look at C compilers instead of C++, as it has been in C since the C99 standard. — Some programmer dude, Jul 23 '20 at 13:59

score 4 · Accepted Answer · answered Jul 23 '20 at 13:17

I clicked through most of the compilers available at https://godbolt.org/ and it seems that only the Microsoft Visual Studio compiler rejects it. GCC and Clang on several platforms are fine with this code.

Note that it is only an additional support, both compiler can decide to stop accepting the code, as it is non standard.

The array will be on the stack for both compilers.

score 0 · Answer 2 · answered Jul 23 '20 at 13:12

Modern C++ compilers usually don't support arrays with unknown size at compile-time. C style arrays like that allocate memory on the stack, using the "new" keyword" or malloc like in C will allocate them on the heap, though you will need to take care of their deletion then. What you might want to use is std::vector, which is on the "vector" header, it will dynamically allocate memory on the heap, allow for resizing at runtime and take care of it's own deletion when it goes out of scope.

score 0 · Answer 3 · answered Jul 23 '20 at 13:14

0

Using std::vector, which any compiler should support

#include <vector>

int main(){
    int n;
    cin>>n;
    std::vector<int> arr(n);

    cout << "the size of my array is:" << arr.size();
}

answered Jul 23 '20 at 13:14

ttemple

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Which compilers support arrays with a size fixed at runtime and which compilers don't?

3 Answers3