How to Properly Delete Memory Allocated with \'placement new\' in C ?

Memory Management with "placement new" and "delete"

In C , memory allocation and deletion play a crucial role in managing dynamic memory. While the standard "new" and "delete" operators are commonly used, "placement new" and "delete" provide a specialized approach for allocating and deleting memory.

Using "placement new"

The example code snippet presented raises questions about the proper method to delete memory allocated using "placement new." In the code, memory is allocated with the line:

void *mem = ::operator new(sizeof(Buffer) + strlen(charString) + 1);

and then a "Buffer" object is placed at this memory location using "placement new":

Buffer* buf = new(mem) Buffer(strlen(charString));

Memory Deallocation Options

The question arises whether to delete the memory using:

delete (char*)buf;

or simply:

delete buf;

To correctly delete the allocated memory, it's important to adhere to specific guidelines:

1. Delete with the same operator used for allocation: You must delete memory allocated with the "new" operator using the "delete" operator. Since "placement new" was used, you cannot directly call the delete operator on the "Buffer*" pointer.
2. Manually call the destructor: Since "placement new" bypasses the regular object construction process, the destructor must be called manually. This is typically done by calling the destructor directly:

buf->~Buffer();

3. Delete the base memory: After calling the destructor, you can delete the base memory allocated by "::operator new":

::operator delete(mem);

Correct Deallocation:

The correct method for deleting the allocated memory is as follows:

buf->~Buffer();
::operator delete(mem);

By following these steps, you ensure that the memory allocated with "placement new" is properly deallocated, avoiding potential memory leaks.

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