TCP simple server and client (Linux) practical training study four

The procedure is relatively simple, but there are still some things to pay attention to:

1：int main(int argc, char **argv)

Parameters can be passed in when calling the program, for example

./a.out aaa bbb ccc

The above are all parameters passed into the main function. The formal parameter argc in the main function is the number of parameters, and **argv is the array of parameters passed in (using the method argv[index]). In this task, you can set the IP and port. argv[0] is "./a.out" argv[1] is "aaa" 

2：perror  ("socket");

This command is similar to printf, except that it will output the latest error message while printing. It can be used to print errors in certain steps (such as socket connection).

3：

serveraddress.sin_family= AF_INET;//ipv4
serveraddress.sin_addr.s_addr= inet_addr("0.0.0.0");//0.0.0.0是监听所有ip
serveraddress.sin_port=   htons(atoi(argv[1]));//设置为大端（小端：先存储低位，大端：先存储高位）

4: gets has a bug and has no length limit. You can use fgets(buf,100,stdin);//to obtain keyboard input

Demonstration diagram

 Client:

/*
 * @Author: CanEve
 * @Date: 2023-05-12 22:52:38
 * @LastEditTime: 2023-06-02 05:04:20
 * @FilePath: /undefined/home/kali/cprogrames/hqyj_learn/day5/client/tcp_client.c
 * @Description: 网络客户端
 */

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include  <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, char **argv){
    if(argc!=3){
        printf("usage: %s <host> <port>\n",argv[0]);
        return -1;
    }
    int socket_fd = socket(AF_INET, SOCK_STREAM,0);//使用ipv4
    if(-1==socket_fd ){
        perror  ("socket");//可同时打印最近的报错信息
        return  -1;
    }
    struct sockaddr_in serveraddress={0};
    serveraddress.sin_family= AF_INET;//ipv4
    serveraddress.sin_addr.s_addr= inet_addr(/*"127.0.0.1"*/argv[1]);
    serveraddress.sin_port=   htons(/*8888*/atoi(argv[2]));//设置为大端（小端：先存储低位，大端：先存储高位,这里统一一下）
    

    int conn_fd=connect(socket_fd,(struct sockaddr *)&serveraddress,sizeof(serveraddress));//连接
    if(-1==conn_fd){
        perror  ("connect");
        return -1;
    }
    while(1){
        printf("input : ");//前部提示
        fflush(stdout);//刷新缓冲区，printf需要\n刷新
        //gets有bug，没有长度限制
        char buf[1024];
        // gets(buf);
        fgets(buf,100,stdin);//获取键盘输入
        write(socket_fd,buf,strlen(buf));//发送
        if(read(socket_fd,buf,sizeof buf)){//接收
            printf(buf);
            fflush(stdout);
        }
        
    }
    close(socket_fd);//关闭socket
    
    return 0;
}

Server:

/*
 * @Author: CanEve
 * @Date: 2023-05-13 03:24:43
 * @LastEditTime: 2023-06-02 05:32:28
 * @FilePath: /day5/server/tcp_server.c
 * @Description: tcp server
 */
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include  <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
//#include "database.h"
#include <string.h>
#include <stdlib.h>
int main(int argc, char **argv){
    
    if(argc!=2){
        printf("usage: %s  <port>\n",argv[0]);
        return -1;
    }
    // MYDATABASE db;
    // database_init(&db);
    // read_line("save.txt",&db);
    int socket_fd = socket(AF_INET, SOCK_STREAM,0);
    if(-1==socket_fd ){
        perror  ("socket");
        return  -1;
    }
    struct sockaddr_in serveraddress={0},clientaddr={0};
    serveraddress.sin_family= AF_INET;//ipv4
    serveraddress.sin_addr.s_addr= inet_addr("0.0.0.0");//0.0.0.0是监听所有ip
    serveraddress.sin_port=   htons(atoi(argv[1]));//设置为大端（小端：先存储低位，大端：先存储高位）
    
    
    int conn_fd=bind(socket_fd,(struct sockaddr *)&serveraddress,sizeof(serveraddress));//绑定ip和端口
    if(-1==conn_fd){
        perror  ("connect");
        return -1;
    }
    listen(socket_fd,10);//可接受10个（但不能同时连接）
    printf("Server listening on\n");
    while(1){//多次连接
        int client=accept(socket_fd,NULL,NULL/*(struct sockaddr *)&clientaddr,sizeof clientaddr*/);//等待客户端接入
        printf("Client listening on\n");
        char buf[1024];
        while (1)
        {
           memset(buf,0,1024);
            if(read(client,buf,1024)){
                printf("rec -> %s\n",buf);
                if(write(client,buf,strlen(buf))<=0){//返回给客户端
                    break;//客户端断开后等待下一个连接
                }   
                // run_database(buf,client,&db);
            }else{
                break;//客户端断开后等待下一个连接
            }
           
        }
        close(client);
    }
    close(socket_fd);
        //write(client,buf,strlen(buf));
        // char repeat[1024]={"hello\n"};
        // write(client,repeat,6);
    

    return 0;
}

Complete code repository: https://gitee.com/caneve/opencaneve/tree/main/Linux/tcp_server_client