Simple array memory allocation with size dynamic allocated and predetermined size

Question

I was writing a program and suddenly came through a doubt. There are two ways i am assigning static array.

int main ()
{ 
   int a[10];
}
int main()
{
    int N;
    cin >> N;  //assume i input N as 10
    int a[N];
}

How will memory allocation differ in both cases? Will be assigned during runtime in second case?

Could be considered a duplicate of [Does “int size = 10;” yield a constant expression?](http://stackoverflow.com/questions/21273829/does-int-size-10-yield-a-constant-expression/21273849#21273849), short summary Variable length arrays are valid C99 but are not valid C++ but it is supported as an extension in C++ by several compilers. — Shafik Yaghmour, Jul 09 '14 at 15:56
A nitpick, neither of those arrays is 'static'. They are 'auto'. — Tim Lovell-Smith, Jul 09 '14 at 16:03

score 2 · Answer 1 · answered Jul 09 '14 at 16:18

The second way is not allowed. The first way will create memory on the stack. As soon as main() exits it will be de-allocated. If you want dynamic allocation best way is to use new:

int* = new int[N];

But then this way you would have to delete it, in the end. If you're OK with using STL then just go with std::vector:

std::vector<int> a;

score 0 · Answer 2 · answered Jul 09 '14 at 15:59

0

The second one is compiled. But it is wrong. Standard C/C++ does not allow it.

answered Jul 09 '14 at 15:59

Sujith Gunawardhane

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Simple array memory allocation with size dynamic allocated and predetermined size

2 Answers2