Placement New: How to Manage Memory When You Call the Constructor Yourself?

Proper Memory Management with Placement New

Placement new allows programmers to explicitly control memory allocation for objects, but this requires careful handling of both object creation and memory release.

When using placement new, as illustrated in the code provided, the responsibility for memory allocation and deallocation falls on the programmer. After manually allocating memory using new char[], a MyClass object is constructed in that memory using placement new (new( pMemory ) MyClass()).

Unlike the delete operator, which automatically calls both the destructor and de-allocates memory, placement new only calls the constructor. This means that the destructor (pMyClass->~MyClass()) must be called explicitly to release the object's resources.

Setting pMyClass to nullptr after calling the destructor is a recommended practice to ensure that the destroyed object is no longer accessible. However, the destructor does not deallocate the memory allocated earlier.

Therefore, it is crucial to remember that after placement new, the allocated memory remains under the programmer's control and must be explicitly released. Calling operator delete on memory allocated using placement new is incorrect because it was not allocated by operator new.

Placement new is designed not only to work with externally allocated memory but also with internal buffers that may not be allocated through operator new. To prevent unexpected behavior, it is strongly advised to avoid calling operator delete on memory managed by placement new.

Instead, it is recommended to define dedicated classes or structures to handle both storage allocation and destruction, ensuring a proper decoupling of memory management from object creation and destruction. This approach allows for greater flexibility and control over memory management, especially in scenarios where memory is managed through internal buffers or custom allocation schemes.

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