socket編程——C實現服務端與客戶端間通信實現大小寫轉換

編譯環境：VIM (Ubuntu 16.04)

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更新：1）程序加上了對錯誤的處理
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常用函數筆記：Socket編程——常用函數

程序包括服務端（server.c）和客戶端（client.c），客戶端實現從shell中輸入小寫字母，通過socket也就是套接字將數據發給服務端，服務端實現小寫->大寫，再將轉換好的數據發回客戶端。、

執行順序：server ----> client
結束順序：client  ----> server

如果先終止server的話會導致server綁定的端口不能及時被釋放，下次再執行server的時候可能會報錯。

 

server.c
——

#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <ctype.h>
#include <string.h>

#define SERV_IP "127.0.0.1"
#define SERV_PORT 6666

int main()
{
    int lfd,cfd;
    struct sockaddr_in serv_addr, clie_addr;
    socklen_t clie_addr_len;
    char buf[BUFSIZ], clie_IP[BUFSIZ];
    int n, i, ret;

    lfd = socket(AF_INET, SOCK_STREAM, 0);//IPV4,TCP
    if(lfd == -1){
        perror("socket error");
        exit(1);
    } 
    serv_addr.sin_family = AF_INET;//IPV4 與socket()的參數相同
    serv_addr.sin_port = htons(SERV_PORT);//本地字節序(小端)->網絡字節序(大端)
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);//INADDR_ANY:本地任意IP(點分十進制類型)

    ret = bind(lfd ,(struct sockaddr *)&serv_addr, sizeof(serv_addr)); //綁定
    if(ret == -1){
        perror("bind error");
        exit(1);
    } 
    ret = listen(lfd, 128);//設定最大同時連接數，default:128 
    if(ret == -1){
        perror("listen error");
        exit(1);
    } 
    clie_addr_len = sizeof(clie_addr);
    cfd = accept(lfd,(struct sockaddr *)&clie_addr, &clie_addr_len);//accept():接收一個連接
    if(cfd == -1){
        perror("accept error");
        exit(1);
    } 
    printf("client IP:%s, client Port:%d\n", 
            inet_ntop(AF_INET, &clie_addr.sin_addr.s_addr, clie_IP, sizeof(clie_IP)),ntohs(clie_addr.sin_port));
    while(1)
    {
        memset(buf,0,sizeof(buf));
        n = read(cfd, buf, sizeof(buf)); //服務器程序阻塞在這，從客戶端讀取
        if(strcmp(buf, "q\n") == 0) break;
        for(i = 0; i < n; i++)
            buf[i] = toupper(buf[i]);    //小寫 -> 大寫
        write(cfd, buf, n);              //寫回客戶端
    }
    close(lfd);
    close(cfd);

    return 0;
}

 

client.c
——

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <string.h>

#define SERV_IP "127.0.0.1"
#define SERV_PORT 6666
int main()
{
    int cfd, n, ret;
    struct sockaddr_in serv_addr;
    char buf[BUFSIZ];
    cfd = socket(AF_INET, SOCK_STREAM, 0);
    if(cfd == -1){
        perror("socket error");
        exit(1);
    }    
    memset(&serv_addr,0,sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(SERV_PORT);
    inet_pton(AF_INET, SERV_IP, &serv_addr.sin_addr); //字符串"127.0.0.1" ---> 網絡端格式

    ret = connect(cfd, (struct sockaddr *)&serv_addr, (socklen_t)sizeof(serv_addr)); //連接
    if(ret == -1){
        perror("socket error");
        exit(1);
    }    

    while(1)
    {
     fgets(buf,sizeof(buf),stdin); //hello world -- fgets  --->"hello world\n\0"
     write(cfd,buf,strlen(buf));
     n = read(cfd,buf,sizeof(buf));      
     write(STDOUT_FILENO,buf,n);
    }
    close(cfd);
    return 0;
}