How Does `delete[]` Know It\'s Dealing with an Array Pointer?

How Delete[] Accurately Identifies Array Pointers

While the behavior of code involving delete[] pointer is undefined based on the pointer's actual type, let's consider the scenario where the pointer is indeed an array pointer.

Who Determines the Array Status?

The critical question is: how does the system know whether a pointer points to an array or not? Unlike with new[], which explicitly allocates memory for an array, there is no corresponding flag or meta-information stored with the pointer itself.

The Runtime Libraries' Role

The answer lies in the runtime libraries. When an array is allocated using new[], the runtime libraries retain a record of its size. This size information is critical for the safe and controlled deletion of the array through delete[].

Memory Management Complexity

But why not use a single delete syntax for all deletion scenarios? This design decision harkens back to C , which prioritizes cost-efficiency. By separating array and non-array deletions, C ensures that runtime libraries don't incur the overhead of array size information for every allocated memory block.

This distinction allows code that does not employ arrays to avoid unnecessary memory consumption associated with array-related data maintenance. Therefore, delete[] is only invoked for pointers known to be associated with arrays, indicated by the extra array size information stored by the runtime libraries.

In conclusion, the runtime libraries play a crucial role in identifying array pointers and facilitating their correct deletion using delete[]. This mechanism ensures memory safety and performance optimization, balancing code efficiency with the flexibility required for handling diverse memory allocation scenarios.

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