server.c:

#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>

/* socket
 * bind
 * sendto/recvfrom
 */
#define SERVER_PORT 8888

int main(int argc, char **argv)
{
int iSocketServer;
int iSocketClient;
struct sockaddr_in tSocketServerAddr;
struct sockaddr_in tSocketClientAddr;
int iRet;
int iAddrLen;

int iRecvLen;
unsigned char ucRecvBuf[1000];
int iClientNum = -1;

iSocketServer = socket(AF_INET, SOCK_DGRAM, 0);
if (-1 == iSocketServer)
{
printf("socket error!\n");
return -1;
}

tSocketServerAddr.sin_family      = AF_INET;
tSocketServerAddr.sin_port        = htons(SERVER_PORT);  /* host to net, short */
  tSocketServerAddr.sin_addr.s_addr = INADDR_ANY;
memset(tSocketServerAddr.sin_zero, 0, 8);

iRet = bind(iSocketServer, (const struct sockaddr *)&tSocketServerAddr, sizeof(struct sockaddr));
if (-1 == iRet)
{
printf("bind error!\n");
return -1;
}

while (1)
{
iAddrLen = sizeof(struct sockaddr);
iRecvLen = recvfrom(iSocketServer, ucRecvBuf, 999, 0, (struct sockaddr *)&tSocketClientAddr&iAddrLen);
if (iRecvLen > 0)
{
ucRecvBuf[iRecvLen] = '\0';
printf("Get Msg From %s : %s\n", inet_ntoa(tSocketClientAddr.sin_addr), ucRecvBuf);
}
}

close(iSocketServer);
return 0;
}

client.c

#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>

/* socket
 * connect
 * send/recv
 */
#define SERVER_PORT 8888
int main(int argc, char **argv)
{
int iSocketClient;
struct sockaddr_in tSocketServerAddr;

int iRet;
unsigned char ucSendBuf[1000];
int iSendLen;
if (argc != 2)
{
printf("Usage:\n");
printf("%s <server_ip>\n", argv[0]);
return -1;
}

iSocketClient = socket(AF_INET, SOCK_DGRAM, 0);
tSocketServerAddr.sin_family      = AF_INET;
tSocketServerAddr.sin_port        = htons(SERVER_PORT);  /* host to net, short */
  //tSocketServerAddr.sin_addr.s_addr = INADDR_ANY;
  if (0 == inet_aton(argv[1], &tSocketServerAddr.sin_addr))
  {
printf("invalid server_ip\n");
return -1;
}
memset(tSocketServerAddr.sin_zero, 0, 8);
iRet = connect(iSocketClient, (const struct sockaddr *)&tSocketServerAddr, sizeof(struct sockaddr));
if (-1 == iRet)
{
printf("connect error!\n");
return -1;
}

while (1)
{
if (fgets(ucSendBuf, 999, stdin))
{
iSendLen = send(iSocketClient, ucSendBuf, strlen(ucSendBuf), 0);
if (iSendLen <= 0)
{
close(iSocketClient);
return -1;
}
}
}

return 0;
}