Which function can change the size of an allocated memory block?

The function that can change the size of an allocated memory block is realloc(). Here are the steps on how it works:

1. realloc() is a function in C programming language that is used for dynamic memory allocation.

2. It changes the size of the memory block pointed to by the pointer that was previously allocated with malloc(), calloc(), or realloc().

3. The syntax of realloc() function is: void* realloc(void* ptr, size_t new_size);

4. Here, ptr is a pointer to the memory block that we want to reallocate memory of, and new_size is the new desired size for the memory block.

5. realloc() tries to change the size of the memory block in the way that the block remains in the same position. But, if it is not possible to extend the memory block at the same position, realloc() creates a new memory block, copies the old data pointed to by ptr to the new block, deallocates the old block, and then returns a pointer to the new memory block.

6. If ptr is NULL, realloc() behaves the same as malloc().

7. If new_size is zero and ptr is not NULL, then the call is equivalent to free(ptr).

8. If realloc() fails to allocate the new memory block, it returns NULL and the original block is left untouched.