`delete ptr` vs. `delete[] ptr`: Why is One Safe and the Other a Memory Leak?

Is Deleting an Array with delete Equivalent to delete[]?

When dealing with dynamic arrays, it's crucial to understand the difference between deleting individual elements with delete and deleting the entire array with delete[].

Why delete ptr Can Cause Undefined Behavior

In the provided code:

IP_ADAPTER_INFO *ptr = new IP_ADAPTER_INFO[100];

ptr points to an array of 100 IP_ADAPTER_INFO structures. Deleting the pointer with delete ptr is equivalent to deleteing the first element of the array. However, this leaves the remaining 99 elements allocated. This can lead to a memory leak.

Disassembly Code Analysis

The disassembly code generated by Visual Studio 2005 for delete ptr and delete []ptr clearly demonstrates the difference:

• delete ptr: Only frees the memory pointed to by ptr (the first element).
• delete []ptr: Calls operator delete[] which correctly deallocates the entire array.

Conclusion

To avoid undefined behavior and prevent memory leaks, always use delete []ptr to deallocate arrays dynamically allocated with new. Despite some compilers might handle delete ptr gracefully, it's an unreliable practice and should be avoided.

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