Question

I have a question regarding copying pointers in the stl library. Say I define:

struct A{
int x;
}

std::map<int, const A*> map1;

I then populate map1 using memory from the heap using malloc for the pointer to A.

Then I do

std::map<int, const A*> map2 = map1;

For each pointer of struct A in map2, does std::map do a shallow copy of the pointers, or assign new memory from the heap for each of the pointers?

Cheers

Shanker

Answer 1

It will copy just the pointers. That means that a shallow copy will be made as opposed to a deep copy. You can easily check the actual behavior by using a simple test program:

int main() {
    std::map<int, int*> map1;        
    map1[0] = new int(10);

    std::map<int, int*> map2 = map1;
    *(map2[0]) = 20;

    // this must print 20 if a shallow copy is used
    std::cout << *(map1[0]) << std::endl;
}