C函数返回错误的数组

Question

I am trying to create a function called getSortedRanks which returns an array. I copied the format for returning arrays from this question Return array in a function but the array is not being returned correctly.

#include <stdlib.h>
#include <stdio.h>
#define familyMembers 4

int *getSortedRanks()
{
    int rankedMembers[familyMembers] = {3,4,2,1};
    return rankedMembers;
}

int main()
{
    int *sortedRanks = getSortedRanks();

    //print the returned array
    for(int i = 0; i < familyMembers; i ++)
    {
        cout << "ranked member is " << sortedRanks[i] << endl;
    }

    return 0;
}

When I run this the output is:

ranked member is 3
ranked member is 0
ranked member is 0
ranked member is 2686744

The first element of the array sortedRanks is always correct but the others are not. How can I correct the way the array is being returned?

Answer 1

An array with automatic storage duration:

int rankedMembers[familyMembers] = {3, 4, 2, 1};

lives on the stack and gets destroyed after getSortedRanks finishes. The returned pointer is invalidated. Dereferencing it leads to undefined behavior .

You'll either want to:

1. Allocate the array dynamically (on the heap), as you'll manage its lifetime:

    int *getSortedRanks() { return new int[familyMembers]{3, 4, 2, 1}; } 

   Don't forget to delete [] it after the use. Using smart pointer will help you with that.

2. Use std::vector or std::array and return by value:

    std::array<int, familyMembers> getSortedRanks() { return {3, 4, 2, 1}; } 

(ordered from less to more favorable)