基于TCP实现

server代码:

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

int main(){
    // SOCK_STREAM为TCP   SOCK_DGRAM为UDP
    int serv_sock = socket(AF_INET, SOCK_STREAM, 0);

    //将套接字和IP、端口绑定
    struct sockaddr_in serv_addr;
    memset(&serv_addr, 0, sizeof(serv_addr));  //每个字节都用0填充
    serv_addr.sin_family = AF_INET;  //使用IPv4地址
    serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");  //具体的IP地址
    serv_addr.sin_port = htons(1234);  //端口
    bind(serv_sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr));

    //进入监听状态，等待用户发起请求
    listen(serv_sock, 20);

    //接收客户端请求
    struct sockaddr_in clnt_addr;
    socklen_t clnt_addr_size = sizeof(clnt_addr);
    int clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_addr, &clnt_addr_size);

    //读客户端发来的数据
    char buffer[40];
    read(clnt_sock, buffer, sizeof(buffer)-1);
    printf("Message form client: %s\n", buffer);

    //向客户端发送数据
    char str[] = "Hello client!";
    write(clnt_sock, str, sizeof(str));
   
    //关闭套接字
    close(clnt_sock);
    close(serv_sock);

    return 0;
}

client代码:

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

int main(){
    // SOCK_STREAM为TCP   SOCK_DGRAM为UDP
    int sock = socket(AF_INET, SOCK_STREAM, 0);

    //向服务器（特定的IP和端口）发起请求
    struct sockaddr_in serv_addr;
    memset(&serv_addr, 0, sizeof(serv_addr));  //每个字节都用0填充
    serv_addr.sin_family = AF_INET;  //使用IPv4地址
    serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");  //具体的IP地址
    serv_addr.sin_port = htons(1234);  //端口
    connect(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr));
   
    //读取服务器传回的数据
    char str[] = "Hello server!";
    write(sock, str, sizeof(str));

    //读取服务器传回的数据
    char buffer[40];
    read(sock, buffer, sizeof(buffer)-1);
   
    printf("Message form server: %s\n", buffer);
   
    //关闭套接字
    close(sock);

    return 0;
}

sys/socket.h是和硬件相关的内容，不同的系统有不同的实现，例如ununtu系统这个文件在/usr/src/linux-headers-5.4.0-58/include/linux文件夹中。

基于UDP实现

server代码:

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

int main(int argc, char **argv)
{
    int sockfd;
    struct sockaddr_in servaddr;

    sockfd = socket(PF_INET, SOCK_DGRAM, 0);

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(50001);

    bind(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr));

    char recvline[1024];

    recvfrom(sockfd, recvline, 1024, 0, NULL, NULL);

    printf("%s\n", recvline);

    close(sockfd);
    return 0;
}

client代码:

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

int main(int argc, char **argv)
{
    int sockfd;
    struct sockaddr_in servaddr;

    sockfd = socket(PF_INET, SOCK_DGRAM, 0);

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(50001);
    servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");

    char sendline[100];
    sprintf(sendline, "Hello, world!");

    sendto(sockfd, sendline, strlen(sendline), 0, (struct sockaddr *)&servaddr, sizeof(servaddr));

    close(sockfd);

    return 1;
}