Managing Memory for Game Developers - Learn C++ for Game Development - page 214

Listing 22-4. Using unique_ptr and shared_ptr
#include <memory>
class Simple
{
private:
int variable{ 0 };
public:
Simple()
{
std::cout << "Constructed" << std::endl;
}
~Simple()
{
std::cout << "Destroyed" << std::endl;
}
};
int _tmain(int argc, _TCHAR* argv[])
{
using UniqueSimplePtr = std::unique_ptr<Simple>;
UniqueSimplePtr pSimple1{ new Simple() };
std::cout << pSimple1.get() << std::endl;
UniqueSimplePtr pSimple2;
pSimple2.swap(pSimple1);
std::cout << pSimple1.get() << std::endl;
std::cout << pSimple2.get() << std::endl;
using IntSharedPtr = std::shared_ptr<int>;
IntSharedPtr pIntArray1{ new int[16] };
IntSharedPtr pIntArray2{ pIntArray1 };
std::cout << std::endl << pIntArray1.get() << std::endl;
std::cout << pIntArray2.get() << std::endl;
return 0;
}
As the name suggests, unique_ptr is used to ensure that you only have a single reference to
allocated memory at a time. Listing 22-3 shows this in action. pSimple1 is assigned a new Simple
pointer and pSimple2 is then created as empty. You can try initializing pSimple2 by passing it
pSimple1 or using an assignment operator and your code will fail to compile. The only way to pass
the pointer from one unique_ptr instance to another is using the swap method. The swap method
moves the stored address and sets the pointer in the original unique_ptr instance to be nullptr .
The first three lines of output in Figure 22-4 show the addresses stored in the unique_ptr instances.