例子:
//server
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/select.h>

#define MAX_BUF_SIZE (1024)
static char buf[MAX_BUF_SIZE];

int display_address(const char *msg, struct sockaddr_in* p_sin)
{
if(p_sin->sin_family != AF_INET)
{
fprintf(stderr, "Not an Internet socket.\n");
return -1;
}
fprintf(stdout, "%s ==> address is: %s : %d\n", msg, inet_ntoa(p_sin->sin_addr), ntohs(p_sin->sin_port));
return 0;
}

int main()
{
int sock, serv;
struct sockaddr_in sin;
int size;
fd_set set;

FD_ZERO(&set);

serv = socket(AF_INET, SOCK_STREAM, 0);
if (serv == -1)
{
perror("server socket");
return -1;
}

memset(&sin, 0, sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = htonl(INADDR_ANY);
sin.sin_port = htons(1685);

if (bind(serv, (struct sockaddr *)&sin, sizeof(sin)) == -1)
{
perror("server bind");
return -1;
}

listen(serv, 5);

memset(&sin, 0, sizeof(sin));
size = sizeof(sin);
if (getsockname(serv, (struct sockaddr *)&sin, &size) == -1)
perror("serv sockname");
display_address("server socket name", &sin);
sock = accept(serv, NULL, NULL);

if (sock != -1)
{
memset(&sin, 0, sizeof(sin));
size = sizeof(sin);
if (getpeername(sock, (struct sockaddr *)&sin, &size) == -1)
perror("sock peername");
display_address("sock peer name", &sin);
memset(&sin, 0, sizeof(sin));
size = sizeof(sin);
if (getsockname(sock, (struct sockaddr *)&sin, &size))
perror("sock sockname");
display_address("sock socket name", &sin);
}
close(serv);
close(sock);
}

//client
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define MAX_BUF_SIZE (300)
static char buf[MAX_BUF_SIZE] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0};

int main()
{
int sock;
struct sockaddr_in sin;
int size;

sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock == -1)
{
perror("client socket");
return -1;
}

memset(&sin, 0, sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = inet_addr("192.168.21.207");
sin.sin_port = htons(1685);

if (connect(sock, (struct sockaddr *)&sin, sizeof(sin)) == -1)
{
perror("client connect");
return -1;
}
printf("client send %d bytes\n", size);
close(sock);
}

请注意
getpeername()是得到连接上来的客户端信息
getsockname()是得到本地的socket信息