最近在做NAT时写的一个双向链表（vc6.0和linux下测试通过）

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

#define MAX_PEER_LEN 64

typedef unsigned long                    u64_t;
typedef unsigned int                     u32_t;
typedef unsigned short                   u16_t;
typedef unsigned char                    u8_t;
typedef signed char                      s8_t;
typedef u32_t ip_addr_t;
typedef u16_t port_t;

/* gnat header */
typedef struct gnat_hdr
{
 ip_addr_t lcl_addr;            // local address with 32 bytes
 ip_addr_t ref_addr;            // public address with 32 bytes
 ip_addr_t rel_addr;            // relay address with 32 bytes
 port_t lcl_port;               // local port number with 16 bytes
 port_t ref_port;               // public port number with 16 bytes
 port_t rel_port;               // relay port number with 16 bytes
 u16_t type;                    // type of action
 u16_t id_len;                  // length of actual peer id
 u8_t peer_id[MAX_PEER_LEN];    // peer_id with 16 bytes defined in peer_length
}gnat_hdr_t;

typedef struct peer_table{
 gnat_hdr_t *peer;
 struct peer_table *next;
} peer_table;

/* peer list */
typedef struct peer_list
{
 struct peer_table *first;  
 struct peer_table *last;  
 struct peer_table *head;  
} peer_list_t;

peer_list_t pplist;

peer_table *gnat_add_peer(peer_list_t *plist, gnat_hdr_t *peer)
{
 peer_table *ppeer;
 
 ppeer = (peer_table *)calloc(1, sizeof(peer_table));
 ppeer->peer = peer;
 
 if ( ppeer == NULL )
  return(NULL);
 
 if(plist->first) {
  ppeer->next = plist->first->next;
  plist->first->next = ppeer;
 }else{
  ppeer->next = plist->head;
  plist->head  = ppeer;
 }
 
 return ppeer;
}


static peer_table *gnat_search_peer(peer_list_t *plist, u8_t peer_id[]) {
 
 peer_table *pp;
 
 pp = plist->head;
 while(pp) {
  if (!strcmp((char *)pp->peer->peer_id, (const char *)peer_id)) {
   break;
  }
  pp = pp->next;
 }
 
 return pp;
}

static u32_t gnat_destroy_peer(peer_list_t *plist, peer_table *peer)
{
 peer_table  **pp;
 
 pp = &plist->head;
 
 while (*pp) {
  if ( *pp == peer )
   break;
  pp = &((*pp)->next);
 }
 
 if ( *pp == peer) {
  *pp = peer->next;
  
  if (plist->first == peer)
   plist->first = NULL;
  
  if (plist->last == peer )
   plist->last = NULL;
  free(peer);
  
  return (0);
 } else {
  return -1;
 }
 
 return (0);
}

int main(void)
{
 gnat_hdr_t  msg;
    u8_t str[32] = "peerA";
 peer_table *pp;
 
 msg.id_len = 4;
 msg.lcl_addr = 0;
 msg.lcl_port = 0;
 memcpy(msg.peer_id, str, 6);
 msg.ref_addr = 0;
 msg.ref_port =0;
 msg.rel_addr = 0;
 msg.rel_port = 0;
 msg.type = 1;
 
    gnat_add_peer(&pplist, &msg);
 pp = gnat_search_peer(&pplist, str);
 printf("%d\n", pp->peer->id_len);
 gnat_destroy_peer(&pplist, pp);
 if((pp = gnat_search_peer(&pplist, str)) == NULL)
  printf("Delete sucess!\n");
 
 return (0);
}