How does delete[] know the array length in C++? [duplicate]

Question

Imagine I have a pointer to an array of integers and then I want to delete it like I do below:

int * numbers = new int[10];
delete[] numbers;

How does the delete operator knows where the array numbers ends to free that memory (since C++ does not keep track of the length of the array as far as I know)?

Thanks!

Answer 1

It can do it however it wants. There are two common ways:

1. The implementation may use an associative array of allocated pointers mapped to their sizes.

2. The implementation may allocate a few extra bytes at the beginning to store the size and pass a pointer into the block to the caller.