Accessing a list in typedef struct

Question

typedef char Word[ WORD_LEN + 1 ];

typedef struct {
    Word list[ MAX_WORDS ];

} FIFO;

So I have a pointer to a FIFO struct, and I'm curious as to what the best way is to access the list inside. I have to be able to add and remove words from the list. Any help would be awesome, thanks!

Answer 1

Let's talk about your choices for representing a FIFO, which will clear up your confusion about how to access the data. A FIFO is an abstract data type that has two behaviors:

1. Items are removed from the beginning.
2. Items are added to the end.

A FIFO implement should keep track up its beginning and its end, so let's update your FIFO struct.

typedef struct {
    unsigned int begin; /* index to first element */
    unsigned int end; /* index to last element */
    Word list[ MAX_WORDS ];
} FIFO;

Now, we need two functions that implement the two behaviors above. Let's call them fifo_add and fifo_remove. (These are incomplete)

void fifo_add(FIFO * fifo, Word w)
{
    fifo.list[fifo->end] = w;
    fifo->end++;
}

Word fifo_remove(FIFO * fifo)
{
    int i = fifo->begin;
    fifo->begin++;

    return fifo->list[i];
}

I've purposefully left these functions incomplete, but I hope this gets you thinking in the right direction (see this page about circular buffers ). I need to stress that this is only one possible implementation of a FIFO . Many people prefer a linked list based FIFO that would have a struct like this:

typedef struct {
    Word w;
    Node * next;
} Node;

typedef struct {
    Node * head;
    Node * tail;
} FIFO;

Regardless of what implementation you use, the fifo_add and fifo_remove will have the same interface, which isolates your FIFO code from the rest of your program.