一个简单的TCP通信的例子

这篇里面涉及的函数和内部结构体请访问：

http://www.cnblogs.com/bugY/archive/2011/10/26/2225152.html

Server端

/* server.c */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#define MAXLINE 80
#define SERV_PORT 8000
int main(void)
{
        struct sockaddr_in servaddr, cliaddr;
        socklen_t cliaddr_len;
        int listenfd, connfd;
        char buf[MAXLINE];
        char str[INET_ADDRSTRLEN];
        int i, n;
        listenfd = socket(AF_INET, SOCK_STREAM, 0);
        bzero(&servaddr, sizeof(servaddr));//先将结构体清零
        servaddr.sin_family = AF_INET;
        servaddr.sin_addr.s_addr = htonl(INADDR_ANY);//主机地址转化为网络地址
        servaddr.sin_port = htons(SERV_PORT);

        bind(listenfd, (struct sockaddr *)&servaddr,sizeof(servaddr));
        listen(listenfd, 20);
        printf("Accepting connections ...\n");
        while (1) {
                cliaddr_len = sizeof(cliaddr);
                connfd = accept(listenfd,(struct sockaddr *)&cliaddr,&cliaddr_len);//返回一个客户端的socket的整型
                n = read(connfd, buf, MAXLINE);
                inet_ntop(AF_INET, &cliaddr.sin_addr, str,sizeof(str));//转换网络地址，由整型转化为点分十进制
                printf("received from %s at PORT %d\n",str,ntohs(cliaddr.sin_port));
                for (i = 0; i < n; i++)
                        buf[i] = toupper(buf[i]);
                        write(connfd, buf, n);
                        close(connfd);
       }
}

Client端

/* client.c */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#define MAXLINE 80
#define SERV_PORT 8000
int main(int argc, char *argv[])
{
        struct sockaddr_in servaddr;
        char buf[MAXLINE];
        int sockfd, n;
        char *str;

        if (argc != 2) {
                fputs("usage: ./client message\n", stderr);
                exit(1);
        }
        str = argv[1];
        sockfd = socket(AF_INET, SOCK_STREAM, 0);
        bzero(&servaddr, sizeof(servaddr));
        servaddr.sin_family = AF_INET;
        inet_pton(AF_INET, "127.0.0.1", &servaddr.sin_addr);
        servaddr.sin_port = htons(SERV_PORT);

        connect(sockfd, (struct sockaddr *)&servaddr,sizeof(servaddr));
        write(sockfd, str, strlen(str));
        n = read(sockfd, buf, MAXLINE);
        printf("Response from server:\n");
        write(STDOUT_FILENO, buf, n);
        close(sockfd);
        return 0;
}

下面是两个防止接受和发送字符串超长的问题

ssize_t Readn(int fd, void *vptr, size_t n)
{
        size_t  nleft;
        ssize_t nread;
        char   *ptr;
        ptr = vptr;
        nleft = n;
        while (nleft > 0) {
                if ( (nread = read(fd, ptr, nleft)) < 0) {
                        if (errno == EINTR)
                                nread = 0;
                        else
                                return -1;
                } else if (nread == 0)
                        break;
                nleft -= nread;
                ptr += nread;
　　　　 }
        return n - nleft;
}
ssize_t Writen(int fd, const void *vptr, size_t n)
{
        size_t nleft;
        ssize_t nwritten;
        const char *ptr;
        ptr = vptr;
        nleft = n;
        while (nleft > 0) {
                if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
                        if (nwritten < 0 && errno == EINTR)
                                nwritten = 0;
                        else
                                return -1;
                }
                nleft -= nwritten;
                ptr += nwritten;
        }
        return n;
}