通过传递函数长度来声明函数内部的数组

Question

I want to have a function which takes a positive integer, then declares an array, initializes it and print it. The following code works with a GCC compiler but it does not work with an MSVC compiler. I get the error

Error (active) E0028 expression must have a constant value. The value of parameter "Length" (declared at line 5) cannot be used as a constant

1. What is a nice way to do this with an MSVC compiler? and
2. Is there any nice reason for this difference?

My code:

#include <iostream>

using namespace std;

void Print(const int Length)
{
    int Array[Length];
    for (int i = 0; i <= Length - 1; i++)
    {
        Array[i] = i;
        cout << Array[i];
    }
}

int main()
{
    const int L = 5;
    Print(L);
    return 0;
}

Answer 1

As it was pointed out in the comments, you should definitely use std::vector<int> .

If you want the array to live only inside your function Print , you can declare a dynamic array on the stack using new . Be mindfull of memory usage, though, as Print could be called with a big number, and you would get a stack overflow (again, use vector to avoid that).

#include <iostream>

using namespace std;

void Print(const int Length)
{
    int *Array = new int[Length];
    for (int i = 0; i < Length; i++)
    {
        Array[i] = i;
        cout << Array[i];
    }
    delete [] Array;
}

int main()
{
    const int L = 5;
    Print(L);
    return 0;
}

EDIT : Here's the vector-based correct solution :

#include <iostream>
#include <vector>

using namespace std;

void Print(const int Length)
{
    vector<int> Array;
    Array.resize(Length);
    for (int i = 0; i < Length; i++)
    {
        Array[i] = i;
        cout << Array[i];
    }
}

int main()
{
    const int L = 5;
    Print(L);
    return 0;
}

Answer 2

If you really want a dynamically allocated, fixed size array, use an std::unique_ptr instead of an std::vector.

#include <iostream>
#include <memory>

void Print(const int Length){
    std::unique_ptr<int[]> Array = std::make_unique<int[]>(Length);
    for (int i = 0; i < Length; ++i){
        Array[i] = i;
        std::cout << Array[i];
    }
    Array.reset();
}