Implementing a write back fifo cache in C

Question

I am trying to implement a fifo cache into a C program. I have a struct:

struct cache{

int blockid;
int used;
char content[SIZE];
};

I made an array of pointers,

struct cache **buffer[size];

And after allocating this cache with the amount of blocks specified, I am having troubles finding the cache entry that stores the block id given (void *get_cache_block(int id) and returning the cached block. I am not sure how to iterate through my array of pointer. Also inserting a new entry into the cache is a function which I am in need of help!

Thanks ahead for the help.

Answer 1

In the code you have shown, you are allocating an array of pointers to pointers, not pointers to structs, the declaration of your cache should be struct cache *buffer[size]. Finding a cache with a given id is a simple for loop, the gist of which is:

int i;
struct cache *cur;

for (i = 0, cur = buffer[0]; i < size; cur = buffer[++i]) {
    if (cur->blockid == id) {
        break;
    }
}

if (i < size) return cur;
else return 0;

The function get_cache_block should return a struct cache * instead of a void * because a void pointer indicates an unknown type.

Additionally, you'll probably want to use a ring buffer for caching, as it has the nice property of overwriting the oldest entry in the buffer when the cache is full. Hopefully that helps and good luck.