Get Previous Block Size from Footer

Task

Implement the function get_prev_block_size

• Given a pointer to a block_header, read the footer of the PREVIOUS block to get its size
• This only works if the previous block is FREE (has a footer)
• The footer is located at the 8 bytes immediately before the current block’s header
• Don’t modify the struct definitions at the top of the file

Function Signature

// Given a pointer to a block_header, read the previous block's footer
// to get its size. Assumes the previous block is free and has a footer.
//
size_t get_prev_block_size(struct block_header* block);

---

Testing

Compiling

• Use gcc to compile the program and use ./ to run the program

$ gcc get_prev_block_size.c -o get_prev_block_size
$ ./get_prev_block_size

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Code

#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
 
struct block_header
{
    size_t size_status;
};
 
struct block_footer
{
    size_t size;
};
 
size_t get_prev_block_size(struct block_header *block)
{
    struct block_footer* footer = (struct block_footer*) block;
    footer -= 1;
    return footer->size;
}