前言

本章节是用基本的Linux/Unix基本函数编写一个完整的服务器和客户端例子，可在Linux(ubuntu)和Unix(freebsd)上运行，客户端和服务端的功能如下:

客户端从标准输入读入一行，发送到服务端

服务端从网络读取一行，然后输出到客户端

客户端收到服务端的响应，输出这一行到标准输出

服务端

代码如下:

#include  <unistd.h>
#include  <sys/types.h>       /* basic system data types */
#include  <sys/socket.h>      /* basic socket definitions */
#include  <netinet/in.h>      /* sockaddr_in{} and other Internet defns */
#include  <arpa/inet.h>       /* inet(3) functions */

#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>

#define MAXLINE 1024
//typedef struct sockaddr  SA;
void handle(int connfd);

int  main(int argc, char **argv)
{
    int     listenfd, connfd;
    int  serverPort = 6888;
    int listenq = 1024;
    pid_t   childpid;
    char buf[MAXLINE];
    socklen_t socklen;

    struct sockaddr_in cliaddr, servaddr;
    socklen = sizeof(cliaddr);

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

    listenfd = socket(AF_INET, SOCK_STREAM, 0);
    if (listenfd < 0) {
        perror("socket error");
        return -1;
    }
    if (bind(listenfd, (struct sockaddr *) &servaddr, socklen) < 0) {
        perror("bind error");
        return -1;
    }
    if (listen(listenfd, listenq) < 0) {
        perror("listen error");    
        return -1;
    }
    printf("echo server startup,listen on port:%d\n", serverPort);
    for ( ; ; )  {
        connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &socklen);
        if (connfd < 0) {
            perror("accept error");
            continue;
        }

        sprintf(buf, "accept form %s:%d\n", inet_ntoa(cliaddr.sin_addr), cliaddr.sin_port);
        printf(buf,"");
        childpid = fork();
        if (childpid == 0) { /* child process */
            close(listenfd);    /* close listening socket */
            handle(connfd);   /* process the request */
            exit (0);
        } else if (childpid > 0)  {
            close(connfd);          /* parent closes connected socket */
        } else {
            perror("fork error");
        }
    }
}


void handle(int connfd)
{
    size_t n;
    char    buf[MAXLINE];

    for(;;) {
        n = read(connfd, buf, MAXLINE);
        if (n < 0) {
            if(errno != EINTR) {
                perror("read error");
                break;
            }
        }
        if (n == 0) {
            //connfd is closed by client
            close(connfd);
            printf("client exit\n");
            break;
        }
        //client exit
        if (strncmp("exit", buf, 4) == 0) {
            close(connfd);
            printf("client exit\n");
            break;
        }
        write(connfd, buf, n); //write maybe fail,here don't process failed error
    } 
} 

客户端

代码如下:

#include  <unistd.h>
#include  <sys/types.h>       /* basic system data types */
#include  <sys/socket.h>      /* basic socket definitions */
#include  <netinet/in.h>      /* sockaddr_in{} and other Internet defns */
#include  <arpa/inet.h>       /* inet(3) functions */
#include <netdb.h> /*gethostbyname function */

#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>

#define MAXLINE 1024

void handle(int connfd);

int main(int argc, char **argv)
{
    char * servInetAddr = "127.0.0.1";
    int servPort = 6888;
    char buf[MAXLINE];
    int connfd;
    struct sockaddr_in servaddr;

    if (argc == 2) {
        servInetAddr = argv[1];
    }
    if (argc == 3) {
        servInetAddr = argv[1];
        servPort = atoi(argv[2]);
    }
    if (argc > 3) {
        printf("usage: echoclient <IPaddress> <Port>\n");
        return -1;
    }

    connfd = socket(AF_INET, SOCK_STREAM, 0);

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(servPort);
    inet_pton(AF_INET, servInetAddr, &servaddr.sin_addr);

    if (connect(connfd, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0) {
        perror("connect error");
        return -1;
    }
    printf("welcome to echoclient\n");
    handle(connfd);     /* do it all */
    close(connfd);
    printf("exit\n");
    exit(0);
}

void handle(int sockfd)
{
    char sendline[MAXLINE], recvline[MAXLINE];
    int n;
    for (;;) {
        if (fgets(sendline, MAXLINE, stdin) == NULL) {
            break;//read eof
        }
        /*
        //也可以不用标准库的缓冲流,直接使用系统函数无缓存操作
        if (read(STDIN_FILENO, sendline, MAXLINE) == 0) {
            break;//read eof
        }
        */

        n = write(sockfd, sendline, strlen(sendline));
        n = read(sockfd, recvline, MAXLINE);
        if (n == 0) {
            printf("echoclient: server terminated prematurely\n");
            break;
        }
        write(STDOUT_FILENO, recvline, n);
        //如果用标准库的缓存流输出有时会出现问题
        //fputs(recvline, stdout);
    }
}

编译和启动服务器:

gcc echoserver.c -o echoserver
./echoserver

编译和启动客户端

gcc echoclient.c -o echoclient
./echoclient

标签：MAXLINE,Socket,int,printf,Unix,Linux,connfd,include,servaddr
来源： https://blog.csdn.net/daocaokafei/article/details/113813452