如何初始化一个很长的数组？

Question

I am just trying to initialize a huge array. My code is given below:

#include<iostream>
using namespace std;

int main()
{
    int T;
    cin >> T;
    while (T--) 
    {
        int d;
        cin >> d;
        int arr[d + 1];
        for (int i = 0; i <= d; i++)
            arr[i] = 0;
    }
    return 0;
}

Now when I input

1 502334160

then I got error Runtime Error - SIGSEGV .

I want to know how to initialize this type of array.

Answer 1

The array may be too big to fit in your program's stack address space. If you allocate the array on the heap you should be fine.

int* arr = new int[d + 1];

But remember that this will require you to delete[] the array. A better solution would be to use std::vector<int> and resize it to d + 1 elements.

Answer 2

First: Variable length arrays (VLA) are illegal in C++. It might be an extension (as it is in gcc), but it won't build on all compilers.

Second: You can initialize an array with brace initialization. If you don't specify all elements, the others will get default value of 0 (in case of int ). So:

int arr[SIZE] {} //specify 0 elements -> all initialized to value 0

Third thing: you allocate your array on stack, so when you create an array of length 1502334160 than it's stack overflow. This amount of ints (assuming 4 bytes each) is almost 6GB of memory while stack is usually 1-2MB.