Is it Safe to Delete a Void Pointer Directly in C ?

The Perils of Deleting Void Pointers

In C , memory management is crucial, and understanding the proper usage of pointers is paramount. A common question arises when dealing with void pointers: is it safe to delete a void pointer directly?

Question:

Consider the following code:

void *my_alloc(size_t size) {
  return new char[size];
}

void my_free(void *ptr) {
  delete[] ptr;
}

Is this code safe, or must ptr be cast to char* before deletion?

Answer:

Deleting a void pointer is explicitly forbidden by the C Standard. Section 5.3.5/3 states that:

In the second alternative (delete array) if the dynamic type of the object to be deleted differs from its static type, the behavior is undefined.

This means that deleting an object using a void pointer is undefined because there are no objects of type void.

In simpler terms, a void pointer has no type information, so it cannot contain the necessary information to properly delete the allocated memory. Deleting via a void pointer may corrupt the memory heap and lead to unpredictable behavior or program crashes.

Therefore, it is essential to avoid deleting via void pointers and instead cast the void pointer to its appropriate type before deletion. In the given example, it would be necessary to cast ptr to char* before calling delete[]:

void my_free(void *ptr) {
  delete[] static_cast<char*>(ptr);
}

By following this practice, you ensure that the memory is correctly deallocated, avoiding potential errors and maintaining the integrity of your program.

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