点对点 客户端-服务器 聊天程序

　　服务器，客户端都是父进程、子进程分别负责发送、接收字符串。

　　另外使用了信号函数来发送和接收处理信号，比如当子进程结束时，传递一个信号给父进程，然后父进程会执行信号处理函数。

服务器端：

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

void handler(int sig)//这是信号处理函数
{
    printf("recv a sig:%d",sig);
    exit(EXIT_SUCCESS);
}

int main()
{
    int sockfd=socket(AF_INET,SOCK_STREAM,0);
    if(sockfd<0) perror("socket!!!!");
    
    int on=1;
    int result=setsockopt(sockfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on));//启用套接字选项，必须在bind之前完成
    if(result<0) perror("setsockopt");

    struct sockaddr_in server_addr;
    memset(&server_addr,0,sizeof(server_addr));
    server_addr.sin_family=AF_INET;
    server_addr.sin_port=htons(888);
    server_addr.sin_addr.s_addr=htonl(INADDR_ANY);


    int res=bind(sockfd,(struct sockaddr*)&server_addr,sizeof(server_addr));
    if(res<0）perror("bind!!!");

    res=listen(sockfd,50);
    if(res<0) perror("listen!!");

    int conn_fd;
    struct sockaddr_in peeraddr;
    int addr_len=sizeof(peeraddr);
    pid_t pid;
    
        conn_fd=accept(sockfd,(struct sockaddr*)&peeraddr,&addr_len);
                if(conn_fd<0)perror("accept!!");
        printf(" the ip of client:%s,the port of client:%d
",inet_ntoa(peeraddr.sin_addr),ntohs(peeraddr.sin_port));//打印对等方的ip与端口
        
        //signal(SIGUSR1,handler);
        pid=fork();
        if(pid<0)
            perror("fork failed");
        else if(pid==0)
        {            //子进程
            char recvbuf[1024]={0};
            while(1)
            {
                memset(recvbuf,0,sizeof(recvbuf));
                int resu;
                resu=read(conn_fd,recvbuf,sizeof(recvbuf));
                if(resu<0)perror("read");
                else if(resu==0)
                { 
                    printf("peer closed!!!!");
                    //exit(EXIT_SUCCESS);
                    kill(getppid(),SIGUSR1);//发送一个信号给父进程
                    break;
                }
                fputs(recvbuf,stdout);
            }
            //close(conn_fd);
            //close(sockfd);
            exit(EXIT_SUCCESS);
        }
        else //父进程
        {
            signal(SIGUSR1,handler);//安装信号接收函数
            char sendbuf[1024]={0};
            while(fgets(sendbuf,sizeof(sendbuf),stdin)!=NULL)
            {
                write(conn_fd,sendbuf,strlen(sendbuf));
                memset(sendbuf,0,sizeof(sendbuf));
        }
        //close(conn_fd);
        //close(sockfd);
        exit(EXIT_SUCCESS);
        }
        return 0;
}

客户端：

#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<errno.h>
#include<netinet/in.h>
#include<string.h>
#include<stdlib.h>
int main()
{
    int sockfd= socket(AF_INET,SOCK_STREAM,0);
    if(sockfd<0)perror("socket");

    struct sockaddr_in server_addr;
    memset(&server_addr,0,sizeof(server_addr));
    server_addr.sin_family=AF_INET;
    server_addr.sin_port=htons(888);    //this port number is owned by server,and client's port number is appointed by random
    server_addr.sin_addr.s_addr=inet_addr("127.0.0.1");//服务器端的ip地址

    int res=connect(sockfd,(struct sockaddr*)&server_addr,sizeof(server_addr));
    if(res<0)perror("connect!!!!!!!");

    pid_t pid;
    pid=fork();
    if(pid<0)perror("fork");
    if(0==pid)//子进程
    {
        char recvbuf[1024];
        int ret;
        while(1)
        {
            memset(recvbuf,0,sizeof(recvbuf));//防止空间中的内容干涉，拖泥带水
            ret=read(sockfd,recvbuf,sizeof(recvbuf));
            if(ret<0)perror("read");
            if(ret==0)
            {
                printf("peer closed!!!!!!!");
                break;
            }
            fputs(recvbuf,stdout);
        }
        close(sockfd);
    }
    else
    {
        char sendbuf[1024];
        while(fgets(sendbuf,sizeof(sendbuf),stdin)!=NULL){
        write(sockfd,sendbuf,strlen(sendbuf));
        memset(sendbuf,0,sizeof(sendbuf));
    }
    //exit(EXIT_SUCCESS);}
    close(sockfd);
    }
    return 0;
}