基于Linux内核的socket编程(TCP)的C语言示例

原文地址：https://www.geeksforgeeks.org/socket-programming-cc/

服务端：

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

#define PORT 8080

int main(int argc, char const* argv[])
{
    int server_fd, new_socket;
    ssize_t valread;
    struct sockaddr_in address;
    int opt = 1;
    socklen_t addrlen = sizeof(address);
    char buffer[1024] = { 0 };
    const char* hello = "Hello from server";

    // AF_INET表示IPV4网络通信领域。SOCKET_STREAM表示TCP，即流式。0表示默认(也可以填6表示TCP)
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // SOL_SOCKET表示套接字级别的选项。SO_REUSEADDR表示服务关闭后，地址和端口可重入。这段可删
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt))) {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }

    address.sin_family = AF_INET; //设置协议簇为IPV4
    address.sin_addr.s_addr = INADDR_ANY; //设置服务端接收的套接字的IP地址，INADDR_ANY表示任何本地地址
    address.sin_port = htons(PORT);//设置端口号为8080

    // Forcefully attaching socket to the port 8080
    // 强制绑定，意思是不管之前是否有其他进程在使用8080端口
    if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    //最多允许3个请求处于半连接状态真正连接成功的会走到accept()函数
    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    printf("waiting for connecting...\n");

    if ((new_socket = accept(server_fd, (struct sockaddr*)&address, &addrlen)) < 0) {
        perror("accept");
        exit(EXIT_FAILURE);
    }
     //从new_socket中读取数据，存入buffer中，长度-1是为了存放字符串的结束符
    valread = read(new_socket, buffer,1024 - 1);
    printf("%s\n", buffer);
    send(new_socket, hello, strlen(hello), 0);
    printf("Hello message sent\n");

    // closing the connected socket
    close(new_socket);
    // closing the listening socket
    close(server_fd);
    return 0;
}

客户端：

// 需要先运行服务端
#include <arpa/inet.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
#define PORT 8080

int main(int argc, char const* argv[])
{
    int status, valread, client_fd;
    struct sockaddr_in serv_addr;
    const char* hello = "Hello from client";
    char buffer[1024] = { 0 };
    if ((client_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("\n Socket creation error \n");
        return -1;
    }

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

    // 将地址转换成二进制
    if (inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr) <= 0) {
        perror("Invalid address");
        return -1;
    }

    //TCP使用connect()函数建立连接，之后就可以send()和read()了。而UDP无需建立连接，直接使用sendto()和recvfrom()函数
    if ((status = connect(client_fd, (struct sockaddr*)&serv_addr, sizeof(serv_addr))) < 0) {
        perror("Connection Failed");
        printf("You should run server side firstly\n");
        return -1;
    }

    send(client_fd, hello, strlen(hello), 0);
    printf("Hello message sent\n");
     //从client_fd中读取数据，存入buffer中，长度-1是为了存放字符串的结束符
    valread = read(client_fd, buffer, 1024 - 1);
    printf("%s\n", buffer);

    // closing the connected socket
    close(client_fd);
    return 0;
}