ringbuf的一个简单实现

/* Opaque buffer element type.  This would be defined by the application. */
typedef struct { void * buff; } ElemType;
 
/* Circular buffer object */
typedef struct {
    int         size;   /* maximum number of elements           */
    int         start;  /* index of oldest element              */
    int         end;    /* index at which to write new element  */
    ElemType   *elems;  /* vector of elements                   */
} CircularBuffer;
 
void cbInit(CircularBuffer *cb, int size) {
    cb->size  = size + 1; /* include empty elem */
    cb->start = 0;
    cb->end   = 0;
    cb->elems = (ElemType *)calloc(cb->size, sizeof(ElemType));
}
 
void cbFree(CircularBuffer *cb) {
    free(cb->elems); /* OK if null */ }
 
int cbIsFull(CircularBuffer *cb) {
    return (cb->end + 1) % cb->size == cb->start; }
 
int cbIsEmpty(CircularBuffer *cb) {
    return cb->end == cb->start; }

int cbCount(CircularBuffer *cb) {
    return (cb->end + cb->size - cb->start) % cb->size; }
	
/* Write an element, overwriting oldest element if buffer is full. App can
   choose to avoid the overwrite by checking cbIsFull(). */
void cbPut(CircularBuffer *cb, ElemType *elem) {
    cb->elems[cb->end] = *elem;
    cb->end = (cb->end + 1) % cb->size;
    if (cb->end == cb->start)
        cb->start = (cb->start + 1) % cb->size; /* full, overwrite */
}
 
/* Read oldest element. App must ensure !cbIsEmpty() first. */
void cbGet(CircularBuffer *cb, ElemType *elem) {
    *elem = cb->elems[cb->start];
    cb->start = (cb->start + 1) % cb->size;
}