socket通信的简单实现

感觉socket的用法还是需要好好耐心的研究一下，先把理论的看懂，包括什么是socket，有哪些数据结构，哪些重要的函数和原理，再把人家的代码一句句看懂，最后最好自己写出来实践一下。不管的写的怎么样，总是自己的代码最好看懂。而且自己写的东西要负责，毕竟还是自己看的多。

下面是我参考人家的代码（其实都差不多），修修补补的写的一个实例，因为在Linux下的socket实现比较容易，更容易帮助理解socket的用法和原理。但是功能也比较简单，写的不清楚的请不吝赐教！

server.c

/*
* Filename: server.c
* version 1.0
* Author :	Halfish
* Last edit time: March 2nd, 2014
*/

#include <netinet/in.h>   // for sockaddr_in
#include <sys/types.h>    // for socket
#include <sys/socket.h>   // for socket
#include <stdio.h>        // for printf
#include <errno.h>        // for errno
#include <stdlib.h>       // for exit
#include <string.h>       // for memset

#define SERVER_PORT   6666
#define LENGTH_OF_LISTEN_QUEUE 20
#define BUFFER_SIZE 1024

int main(int argc, char const *argv[])
{

// 设置一个服务器端的socket地址结构server_addr,代表服务器internet地址, 端口
struct sockaddr_in server_addr;

int server_socket_fd; // 服务器端的文件描述符

// define buffer to receive/send string from/to client
char buffer_receive[BUFFER_SIZE];
memset(buffer_receive, 0, BUFFER_SIZE);
char buffer_send[BUFFER_SIZE];
memset(buffer_send, 0, BUFFER_SIZE);

/*
* try to initialize to server address
*/
memset(&server_addr, 0, sizeof(server_addr)); //把一段内存区的内容全部设置为0
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = htons(INADDR_ANY);
server_addr.sin_port = htons(SERVER_PORT);

/*
* try to creat a server socket
*/
server_socket_fd = socket(AF_INET, SOCK_STREAM, 0);
if (server_socket_fd == -1)
{
// only return -1 means fail and set errno simultaneously
printf("	Failed to creat a socket for server...\n");
printf("	(errno: %d) %s\n", errno, strerror(errno) );
return 1;
}
else
{
printf("	Successfully creat a socket for server...\n");
}

/*
* try to bind the server_socket_fd and server_addr
*/
if( bind(server_socket_fd,(struct sockaddr*)&server_addr, sizeof(server_addr) ) == -1)
{
// only return -1 means fail and set errno simultaneously
printf("	Failed to bind this port: %d \n", SERVER_PORT);
printf("	(errno: %d) %s\n", errno, strerror(errno) );
return 1;
}
else
{
// only bind returns 0 means bind successfully ?!
printf("	Bind successfully\n");
}

/*
* the server begins to listen
*/
if ( listen(server_socket_fd, LENGTH_OF_LISTEN_QUEUE) == -1)
{
printf("	Failed to listen...");
printf("	(errno: %d) %s \n", errno, strerror(errno));
return 1;
}
else
{
printf("	Server is listening...\n");
}

/*
* begin connections to multiple clients
*/
while(1)
{
struct sockaddr_in client_address;
socklen_t length = sizeof(client_address);

/*
*
* 接受一个到server_socket代表的socket的一个连接
* 如果没有连接请求,就等待到有连接请求--这是accept函数的特性
* accept函数返回一个新的socket,这个socket(new_server_socket_fd)用于同连接到的客户的通信
* new_server_socket_fd代表了服务器和客户端之间的一个通信通道
* accept函数把连接到的客户端信息填写到客户端的socket地址结构client_address中
*
*/
int new_server_socket_fd = accept(server_socket_fd, (struct sockaddr*)&client_address, &length);
if ( new_server_socket_fd < 0)
{
printf("	Failed to accept a connection from to client!\n");
printf("	(errno: %d) %s\n", errno, strerror(errno) );
break;
}
else
{
printf("	Accepted a client successfully\n");
}

// Thread added here

// accepted connection, begin a dead loop to receive information from one specific client
while(1)
{
/*
* recieve data from client
*/
memset(buffer_receive, 0, BUFFER_SIZE);

length = recv(new_server_socket_fd, buffer_receive, BUFFER_SIZE, 0);
if (length < 0)
{
printf("	Failed to recieve data from client. \n" );
printf("	(errno: %d) %s\n", errno, strerror(errno) );
continue;
}
else
{
printf("	Client said:");
printf("	%s\n", buffer_receive);
}

/*
* scanf from stdin continuously and send to client simutaneously
*/
printf("	Server(it's me) said:	");
memset(buffer_send, 0, BUFFER_SIZE);
scanf("%s", buffer_send);
if (send(new_server_socket_fd, buffer_send, sizeof(buffer_send), 0) < 0)
{
printf("	Failed to send data to client. \n" );
printf("	(errno: %d) %s\n", errno, strerror(errno) );
continue;
}
} // end of while(1)
close(new_server_socket_fd);
}

close(server_socket_fd);

return 0;
}

client.c

/*
* Filename: client.c
* version 1.0
* Author :	Halfish
* Last edit time: March 2nd, 2014
*/

#include <netinet/in.h>   // for sockaddr_in
#include <sys/types.h>    // for socket
#include <sys/socket.h>   // for socket
#include <stdio.h>        // for printf
#include <errno.h>        // for errno
#include <stdlib.h>       // for exit
#include <string.h>       // for memset

#define SERVER_PORT  6666
#define BUFFER_SIZE  1024

int main(int argc, char const *argv[])
{

if (argc != 2)
{
printf("    You must tell me the address of server! \n");
return 0;
}

/*
* initilize client
*/
int client_socket_fd = socket(AF_INET,SOCK_STREAM,0);
if (client_socket_fd == -1)
{
// only return -1 means fail and set errno simultaneously
printf("    Failed to creat a socket for client.\n");
printf("    (errno: %d) %s\n", errno, strerror(errno) );
return 1;
}
else
{
printf("    Successfully initilize the client !\n");
}

/*
* initilize server address
*/
struct sockaddr_in server_address;
memset(&server_address, 0, sizeof(server_address));
server_address.sin_family = AF_INET;

if (inet_aton(argv[1],&server_address.sin_addr) == 0)  // inet_aton() = address to number
{
printf("    Server's IP address error!\n");
printf("    (errno: %d) %s\n", errno, strerror(errno) );
return 1;
}
server_address.sin_port = htons(SERVER_PORT);
socklen_t server_addr_length = sizeof(server_address);

/*
* begin to connect to server
*/
if ( connect(client_socket_fd, (struct sockaddr*) &server_address, server_addr_length) == -1)
{
printf("    Can not connect to %s!\n", argv[1]);
printf("    (errno: %d) %s\n", errno, strerror(errno) );        return 1;
}
else
{
printf("    Successfully connect to server! \n");
}

/*
* define buffer to receive/send string from/to server
*/
char buffer_receive[BUFFER_SIZE];
char buffer_send[BUFFER_SIZE];
memset(buffer_receive, 0, BUFFER_SIZE);
memset(buffer_send, 0, BUFFER_SIZE);

strcpy(buffer_send, "    I am the client, can you hear me ? ");
if (send(client_socket_fd, buffer_send, sizeof(buffer_send), 0) < 0)
{
printf("    Failed to send data to client. \n" );
printf("    (errno: %d) %s\n", errno, strerror(errno) );
return 0;
}

// accepted connection, begin a dead loop to receive information from one specific client
int i = 1;
while(i)
{
printf("%d\n", i);
++ i;
/*
* recieve data from server
*/
memset(buffer_receive, 0, BUFFER_SIZE);
socklen_t length = sizeof(server_address);

length = recv(client_socket_fd, buffer_receive, BUFFER_SIZE, 0);
if (length < 0)
{
printf("    Failed to recieve data from server. \n" );
printf("    (errno: %d) %s\n", errno, strerror(errno) );
continue;
}
else
{
printf("    Server said:");
printf("    %s\n", buffer_receive);
}

/*
* scanf from stdin continuously and send to server simutaneously
*/
printf("    Client(it's me) said:   ");
memset(buffer_send, 0, BUFFER_SIZE);
scanf("%s", buffer_send);
if (send(client_socket_fd, buffer_send, sizeof(buffer_send), 0) < 0)
{
printf("    Failed to send data to server. \n" );
printf("    (errno: %d) %s\n", errno, strerror(errno) );
continue;
}
} // end of while(1)

close(client_socket_fd);

return 0;
}