如何释放 function 中分配的 memory 而不返回其指针？

Question

I have a function like this:

int fun(){
    int* arr = new int[10];
    for(int i = 0; i < 10; i++){
        arr[i] = 5;
    }
    delete[] arr;  // 
    return arr[6];
}

int main(){
    std::cout << fun();
    return 0;
} 

What am i going to do is to free the memory whick is pointed to by the pointer arr . But the function is not returning pointer arr . So i tryed to free it inside the function.
It won't print anything if delete[] arr is above return arr[6] (Using Visual Studio 2019).
But if return arr[6] is above delete[] arr , would the memory be freed or this sentence be skipped?
Or should i declare arr inside main() then free it in main() ?

Answer 1

Unless it's for academic purposes, you rarely see a C++ program using manual memory allocation, you don't need to do it since you have a set of containers in the STL containers library that do this memory management reliably for you. In your particular example, a std::vector is recommended.

That said, to answer your question:

It won't print anything if delete[] arr is above return arr[6] (Using Visual Studio 2019).

If you delete the array before accessing the data stored in it the behavior is undefined. It's only natural that it doesn't print anything. It could also print the expected result , that's one of the features of undefined behavior . Using Visual Studio or not, it's the same.

But if return arr[6] is above delete[] arr , would the memory be freed or this sentence be skipped?

Yes it would be skipped, or more accurately, all code after the return statement will not be executed. The memory will not be freed.

Or should I declare arr inside main() then free it in main() ?

If the data should belong in the main 's scope you should definitely declare it there, you can pass it to the function as an argument:

#include <cassert>
#include <iostream>

int fun(int* arr) {
    assert(arr);
    for (int i = 0; i < 10; i++) {
        arr[i] = 5;
    }
    return arr[6];
}

int main() {
    int* arr = new int[10];
    std::cout << fun(arr);
    delete[] arr;
    return 0;
}