Memory not being free in nested objects - c++

Question

I found this memory leak from Valgrind which gave the memory error: Invalid free() / delete / delete[] / realloc().
==7367== Invalid free() / delete / delete[] / realloc()
==7367== at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7367== by 0x40077F: ItemSet::~ItemSet() (cart.cpp:33)
==7367== by 0x40086B: ShoppingCart::~ShoppingCart() (cart.cpp:14)
==7367== by 0x400828: main (cart.cpp:45)
==7367== Address 0x5a1c0b0 is 0 bytes inside a block of size 40 free'd
==7367== at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7367== by 0x40077F: ItemSet::~ItemSet() (cart.cpp:33)
==7367== by 0x400800: ShoppingCart::ShoppingCart() (cart.cpp:39)
==7367== by 0x400817: main (cart.cpp:43)
==7367==
==7367==
==7367== HEAP SUMMARY:
==7367== in use at exit: 40 bytes in 1 blocks
==7367== total heap usage: 2 allocs, 2 frees, 80 bytes allocated
==7367==
==7367== LEAK SUMMARY:
==7367== definitely lost: 40 bytes in 1 blocks
==7367== indirectly lost: 0 bytes in 0 blocks
==7367== possibly lost: 0 bytes in 0 blocks
==7367== still reachable: 0 bytes in 0 blocks
==7367== suppressed: 0 bytes in 0 blocks
==7367== Rerun with --leak-check=full to see details of leaked memory
==7367==
==7367== For counts of detected and suppressed errors, rerun with: -v
==7367== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
Here is the code. Its a simplified version of my program, but it still has the problem I am having.
#include <cstdlib>
class ItemSet {
private:
int* items;
public:
ItemSet();
virtual ~ItemSet();
// ItemSet Methods...
};
class ShoppingCart {
private:
ItemSet items_in_cart;
public:
ShoppingCart();
// ShoppingCart methods...
};
ItemSet::ItemSet() {
// Constructor
int max_num_of_items = 10;
items = (int*)calloc(sizeof(int), max_num_of_items);
}
ItemSet::~ItemSet() {
// Destructor
if (NULL != items) {
// Frees the dynamically allocated register files
free(items);
}
}
ShoppingCart::ShoppingCart() {
// Constructor
items_in_cart = ItemSet();
}
int main() {
ShoppingCart cart = ShoppingCart();
return 0;
}

Answer 1

ShoppingCart::ShoppingCart() {
// Constructor
items_in_cart = ItemSet();
}
That last line can't possibly work. Right after the assignment, we have two ItemSet objects with the same value for items -- the temporary created on the right side and items_in_cart. When the second one is destroyed, you have a double free.
Use a sensible method of having a collection of objects like std::list, std::vector, or std::array. Otherwise, follow the rule of 3, rule of 5, or of zero.