从客户端向服务器端发送信息时，在服务器端有打印显示；

检测环境常用，备份一下

0，公共头文件代码

//config.h

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

const int MAX_LINE = 4096;
const int PORT = 6000;
const int BACKLOG = 10;
const int LISTENQ = 6666;
const int MAX_CONNECT = 20;

1，服务器代码

/*
 * server.c
*/

#include "config.h"

int main(int argc , char **argv)
{
        /*声明服务器地址和客户链接地址*/
        struct sockaddr_in servaddr , cliaddr;

        /*声明服务器监听套接字和客户端链接套接字*/
        int listenfd , connfd;
        pid_t childpid;

        /*声明缓冲区*/
        char buf[MAX_LINE];

        socklen_t clilen;

        /*(1) 初始化监听套接字listenfd*/
        if((listenfd = socket(AF_INET , SOCK_STREAM , 0)) < 0)
        {
                perror("socket error");
                exit(1);
        }//if

        /*(2) 设置服务器sockaddr_in结构*/
        bzero(&servaddr , sizeof(servaddr));

        servaddr.sin_family = AF_INET;
        //servaddr.sin_addr.s_addr = htonl(INADDR_ANY); //表明可接受任意IP地址
        servaddr.sin_addr.s_addr = inet_addr("10.20.30.40");//此处服务器本机ip，可以换成上一行
        servaddr.sin_port = htons(PORT);

        /*(3) 绑定套接字和端口*/
        if(bind(listenfd , (struct sockaddr*)&servaddr , sizeof(servaddr)) < 0)
        {
                perror("bind error");
                exit(1);
        }//if

        /*(4) 监听客户请求*/
        if(listen(listenfd , LISTENQ) < 0)
        {
                perror("listen error");
                exit(1);
        }//if

        /*(5) 接受客户请求*/
        for( ; ; )
        {
                clilen = sizeof(cliaddr);
                if((connfd = accept(listenfd , (struct sockaddr *)&cliaddr , &clilen)) < 0 )
                {
                        perror("accept error");
                        exit(1);
                }//if

                //新建子进程单独处理链接
                if((childpid = fork()) == 0)
                {
                        close(listenfd);
                        //str_echo
                        ssize_t n;
                        char buff[MAX_LINE];
                        while((n = read(connfd , buff , MAX_LINE)) > 0)
                        {
                                write(connfd , buff , n);
                                printf("rec: %s", buff);
                        }
                        exit(0);
                }//if
                close(connfd);
        }//for

        /*(6) 关闭监听套接字*/
        close(listenfd);
}

2，客户端代码

/*
 * client.c
*/

#include "config.h"

/*readline函数实现*/
ssize_t readline(int fd, char *vptr, size_t maxlen)
{
        ssize_t n, rc;
        char    c, *ptr;

        ptr = vptr;
        for (n = 1; n < maxlen; n++) {
                if ( (rc = read(fd, &c,1)) == 1) {
                        *ptr++ = c;
                        if (c == '\n')
                                break;  /* newline is stored, like fgets() */
                } else if (rc == 0) {
                        *ptr = 0;
                        return(n - 1);  /* EOF, n - 1 bytes were read */
                } else
                        return(-1);             /* error, errno set by read() */
        }

        *ptr = 0;       /* null terminate like fgets() */
        return(n);
}


int main(int argc , char ** argv)
{
        /*声明套接字和链接服务器地址*/
        int sockfd;
        struct sockaddr_in servaddr;

        /*判断是否为合法输入*/
        if(argc != 2)
        {
                perror("usage:tcpcli <IPaddress>");
                exit(1);
        }//if

        /*(1) 创建套接字*/
        if((sockfd = socket(AF_INET , SOCK_STREAM , 0)) == -1)
        {
                perror("socket error");
                exit(1);
        }//if

        /*(2) 设置链接服务器地址结构*/
        bzero(&servaddr , sizeof(servaddr));
        servaddr.sin_family = AF_INET;
        servaddr.sin_port = htons(PORT);
        if(inet_pton(AF_INET , argv[1] , &servaddr.sin_addr) < 0)
        {
                printf("inet_pton error for %s\n",argv[1]);
                exit(1);
        }//if

        /*(3) 发送链接服务器请求*/
        if( connect(sockfd , (struct sockaddr *)&servaddr , sizeof(servaddr)) < 0)
        {
                perror("connect error");
                exit(1);
        }//if

        /*(4) 消息处理*/
        char sendline[MAX_LINE] , recvline[MAX_LINE];
        while(fgets(sendline , MAX_LINE , stdin) != NULL)
        {
                write(sockfd , sendline , strlen(sendline));

                if(readline(sockfd , recvline , MAX_LINE) == 0)
                {
                        perror("server terminated prematurely");
                        exit(1);
                }//if

                if(fputs(recvline , stdout) == EOF)
                {
                        perror("fputs error");
                        exit(1);
                }//if
        }//while

        /*(5) 关闭套接字*/
        close(sockfd);
}

3，构建代码

Makefile

all: client server

client: client.c

server:server.c

.PHONY:clean
clean:
        -rm -f server client

4，效果

启动server：

$./server

启动client：

$./client  10.20.30.40