# Circular Buffer
###### tags: `C LANGUAGE` `ring buffer` `circular buffer`
<style>
.blue {
color: blue;
}
.bgblue {
color: blue;
font-size: 24px;
font-weight: bold;
}
.red {
color: red;
font-size: 24px;
font-weight: bold;
}
h1 {text-align: center;}
</style>
Author: CrazyMonkey
email: [e-mail]
Date: 20220726
Copyright: CC BY-NC-SA
另一重要的 [circular buffer](https://en.wikipedia.org/wiki/Circular_buffer) 運用, 尤其是記憶體受限時, 例如 單晶片, embedded system 或資料變動快速與大量時(**使用circular buffer 不需要 經常 malloc, free, 如此可減少 OS 進行garbage collection! )**

Reference source code
**cring.h**

typedef struct _ring_buffer
{
    void *buffer;     // data buffer
    void *buffer_end; // end of data buffer
    size_t capacity;  // maximum number of items in the buffer
    size_t count;     // number of items in the buffer
    size_t sz;        // size of each item in the buffer
    void *head;       // pointer to head
    void *tail;       // pointer to tail
    int (*push)(struct _ring_buffer *pthis,const void *item);
    int (*pop)(struct _ring_buffer *ring, void *item);


} ring_buffer;

/*
byte acces
ring_init( size_t capacity, 1);

*/

ring_buffer * ring_init( size_t capacity, size_t sz);


void ring_exit(ring_buffer *ring);

**cring.c**

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>

#include "cring.h"
static int ring_push(ring_buffer *ring, const void *item)
{
    if(ring->count == ring->capacity){
        return 0;
    }
    memcpy(ring->head, item, ring->sz);
    ring->head =  (unsigned char*)ring->head + ring->sz;
    if(ring->head == ring->buffer_end)
        ring->head = ring->buffer;
    ring->count++;
    return ring->count;
}

static int ring_pop(ring_buffer *ring, void *item)
{
    if(ring->count == 0){
        // handle error
        return 0;
         
    }
    memcpy(item, ring->tail, ring->sz);
    ring->tail = (unsigned char*)ring->tail + ring->sz;
    if(ring->tail == ring->buffer_end)
        ring->tail = ring->buffer;
    ring->count--;
    return ring->count;
}

ring_buffer * ring_init( size_t capacity, size_t sz)
{
    ring_buffer *ring;
    ring=malloc(sizeof(ring_buffer));

    if(ring==NULL)return NULL;

    ring->buffer = malloc(capacity * sz);
    if(ring->buffer == NULL){

       free(ring);
       return NULL;
    }
        
    ring->buffer_end = (unsigned char *)ring->buffer + capacity * sz;
    ring->capacity = capacity;
    ring->count = 0;
    ring->sz = sz;
    ring->head = ring->buffer;
    ring->tail = ring->buffer;
    ring->push=ring_push;
    ring->pop=ring_pop;
}

void ring_exit(ring_buffer *ring)
{
    if(ring){
      free(ring->buffer);
      free(ring);
    }
    
}

HW.