How Do You Manage Memory When Using Placement New?

Proper Memory Management with Placement New

When employing placement new, the responsibility of memory management falls upon the programmer rather than the standard operator delete. This introduces the need for manual destructor invocation and subsequent memory deallocation to prevent memory leaks.

Placement New vs. Operator Delete

Placement new allocates memory and places an object at the specified location. Operator delete, on the other hand, calls the object's destructor and deallocates the memory initially allocated by operator new. However, in the case of placement new, memory allocation is not handled by operator new, necessitating manual memory release.

Calling the Destructor Manually

After calling placement new, the programmer must manually invoke the object's destructor with syntax similar to the following:

<code class="cpp">pMyClass->~MyClass();</code>

This ensures that the destructor properly deinitializes the object.

Setting the Object Pointer to Null

Once the destructor is called, it is generally recommended to set the object pointer to nullptr to avoid accidentally using a dangling pointer.

<code class="cpp">pMyClass->~MyClass();
pMyClass = nullptr;</code>

No Memory Deallocation with the Destructor

Unlike operator delete, the destructor does not perform memory deallocation. Therefore, it is essential to release the memory manually, either through a custom deallocation function or a higher-level memory management facility.

Internal Buffers and Placement New

Placement new is also utilized with internal buffers and other scenarios where memory is not allocated via operator new. In such cases, invoking operator delete would be inappropriate. Instead, the buffer management responsibility lies with the programmer.

Conclusion

When using placement new, proper memory management involves manually calling the destructor and subsequently releasing the allocated memory. This prevents memory leaks and ensures the object is properly deinitialized. It is important to differentiate between placement new and operator delete, as they serve distinct roles in object construction and destruction.

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