Linux中用C语言写一个socket编程示例

### 回答1：
以下是 Linux 中使用 C 语言编写的简单 socket 编程示例:

服务端代码:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h> 
#include <sys/socket.h>
#include <netinet/in.h>

void error(const char *msg) {
    perror(msg);
    exit(1);
}

int main(int argc, char *argv[]) {
    int sockfd, newsockfd, portno;
    socklen_t clilen;
    char buffer[256];
    struct sockaddr_in serv_addr, cli_addr;
    int n;
    if (argc < 2) {
        fprintf(stderr,"ERROR, no port provided\n");
        exit(1);
    }
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) 
       error("ERROR opening socket");
    bzero((char *) &serv_addr, sizeof(serv_addr));
    portno = atoi(argv[1]);
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = INADDR_ANY;
    serv_addr.sin_port = htons(portno);
    if (bind(sockfd, (struct sockaddr *) &serv_addr,
             sizeof(serv_addr)) < 0) 
             error("ERROR on binding");
    listen(sockfd,5);
    clilen = sizeof(cli_addr);
    newsockfd = accept(sockfd, 
                (struct sockaddr *) &cli_addr, 
                &clilen);
    if (newsockfd < 0) 
         error("ERROR on accept");
    bzero(buffer,256);
    n = read(newsockfd,buffer,255);
    if (n < 0) error("ERROR reading from socket");
    printf("Here is the message: %s\n",buffer);
    n = write(newsockfd,"I got your message",18);
    if (n < 0) error("ERROR writing to socket");
    close(newsockfd);
    close(sockfd);
    return 0; 
}

客户端代码:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h> 

void error(const char *msg) {
    perror(msg);
    exit(0);
}

int main(int argc, char *argv[]) {
    int sockfd, portno, n;
    struct sockaddr_in serv_addr;
    struct hostent *  

### 回答2：
以下是一个用C语言编写的简单的Linux socket编程示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h> // close函数
#include <arpa/inet.h> // htons, inet_pton函数
#include <sys/socket.h> // socket, bind, listen, accept, recv, send函数

#define PORT 8080
#define BUFFER_SIZE 1024

int main() {
int server_fd, new_socket, valread;
struct sockaddr_in address;
int opt = 1;
int addrlen = sizeof(address);
char buffer[BUFFER_SIZE] = {0};
char *hello = "Hello from server";

// 创建套接字
if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
perror("Socket creation failed");
exit(EXIT_FAILURE);
}

// 设置套接字选项，允许地址重复使用
if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
perror("Setsockopt failed");
exit(EXIT_FAILURE);
}

address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons(PORT);

// 绑定套接字到指定端口
if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {
perror("Bind failed");
exit(EXIT_FAILURE);
}

// 监听连接请求
if (listen(server_fd, 3) < 0) {
perror("Listen failed");
exit(EXIT_FAILURE);
}

// 接受连接请求
if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen)) < 0) {
perror("Accept failed");
exit(EXIT_FAILURE);
}

// 接收客户端数据
valread = recv(new_socket, buffer, BUFFER_SIZE, 0);
printf("Received: %s\n", buffer);

// 向客户端发送消息
send(new_socket, hello, strlen(hello), 0);
printf("Hello message sent\n");

// 关闭套接字
close(new_socket);
close(server_fd);

return 0;
}

该示例中创建了一个TCP服务器，会监听在8080端口上。当有客户端连接后，会接收客户端发送的消息，并向客户端发送"Hello from server"消息。最后关闭套接字。  

### 回答3：
在Linux系统中，我们可以使用C语言编写一个基本的Socket编程示例。以下是一个简单的Server-Client示例，包括了服务器端和客户端的代码。

服务器端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define PORT 8080
#define BUFFER_SIZE 1024

int main() {
int server_fd, new_socket;
struct sockaddr_in address;
int addrlen = sizeof(address);
char buffer[BUFFER_SIZE] = {0};
char *server_response = "Server is connected!\n";

// 创建Socket
if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
perror("Socket creation failed");
exit(EXIT_FAILURE);
}

address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons(PORT);

// 绑定Socket到指定端口
if (bind(server_fd, (struct sockaddr *)&address, sizeof(address))<0) {
perror("Binding failed");
exit(EXIT_FAILURE);
}

// 监听连接
if (listen(server_fd, 3) < 0) {
perror("Listening failed");
exit(EXIT_FAILURE);
}

// 建立连接
if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen)) < 0) {
perror("Acceptance failed");
exit(EXIT_FAILURE);
}

// 发送欢迎消息
send(new_socket, server_response, strlen(server_response), 0);
printf("Welcome message sent\n");

// 接收客户端消息并发送回复
while (1) {
memset(buffer, 0, sizeof(buffer));
read(new_socket, buffer, BUFFER_SIZE);
printf("Client message: %s\n", buffer);
send(new_socket, buffer, BUFFER_SIZE, 0);
}

return 0;
}

客户端代码：

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

#define PORT 8080
#define BUFFER_SIZE 1024

int main() {
int sock = 0, valread;
struct sockaddr_in serv_addr;
char *client_message = "Hello from client";

char buffer[BUFFER_SIZE] = {0};

// 创建Socket
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
perror("Socket creation failed");
exit(EXIT_FAILURE);
}

serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(PORT);

// 将IPv4地址从点分十进制转换为网络字节序
if(inet_pton(AF_INET, "127.0.0.1", &(serv_addr.sin_addr))<=0) {
perror("Invalid address or address not supported");
exit(EXIT_FAILURE);
}

// 连接到服务器
if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
perror("Connection failed");
exit(EXIT_FAILURE);
}

// 发送消息
send(sock, client_message, strlen(client_message), 0);
printf("Message sent to server\n");

// 接收回复消息
valread = read(sock, buffer, BUFFER_SIZE);
printf("Server message: %s\n", buffer);

return 0;
}

以上代码示例展示了Linux中使用C语言编写Socket通信的基本原理。服务器端使用`socket()`函数创建socket，`bind()`函数将socket绑定到指定的端口，`listen()`函数监听连接请求，并使用`accept()`函数接收来自客户端的连接。客户端使用`socket()`函数创建socket，`connect()`函数连接到服务器，并使用`send()`函数发送消息，`read()`函数接收并打印服务器端回复的消息。

以上示例是一个简单的基于TCP协议的Socket通信示例，可以通过编译并在Linux系统上运行进行测试。