TCP / IP：字符串操作后传输不起作用

Question

我正在尝试在localhost上模拟客户端和服务器之间的简单TCP连接。在“client.c”文件中没有第22行的情况下工作正常，我正在进行字符串操作。如果没有注释该行，服务器显然不会与客户端建立连接 我一直在寻找很长时间，但我发现没有与此严格相关的内容。如果我得到一些帮助，那就太棒了。 :)

文件：

client.c

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

#define BUFLEN 256

void error(char *msg)
{
    perror(msg);
    exit(0);
}

int main(int argc, char *argv[])
{
    int sockfd, n;
    //char filename[] = "file.txt"; // !!THE PROBLEM IS HERE!!
    struct sockaddr_in serv_addr;
    struct hostent *server;

    char buffer[BUFLEN];
    if (argc < 3) {
    fprintf(stderr,"Usage %s server_address server_port\n", argv[0]);
       exit(0);
    }  

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) 
    error("ERROR opening socket");

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(atoi(argv[2]));
    inet_aton(argv[1], &serv_addr.sin_addr);


    if (connect(sockfd,(struct sockaddr*) &serv_addr,sizeof(serv_addr)) < 0) 
        error("ERROR connecting");    

    while(1) {
        memset(buffer, 0 , BUFLEN);
        fgets(buffer, BUFLEN-1, stdin);


        n = send(sockfd,buffer,strlen(buffer), 0);
        if (n < 0) 
             error("ERROR writing to socket");

    }
    return 0;
}

server.c

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

#define MAX_CLIENTS 5
#define BUFLEN 256

void error(char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc, char *argv[])
{
     int sockfd, newsockfd, portno, clilen;
     char buffer[BUFLEN];
     struct sockaddr_in serv_addr, cli_addr;
     int n, i, j;

     fd_set read_fds;
     fd_set tmp_fds; 
     int fdmax;

     if (argc < 2) {
         fprintf(stderr,"Usage : %s port\n", argv[0]);
         exit(1);
     }

     FD_ZERO(&read_fds);
     FD_ZERO(&tmp_fds);

     sockfd = socket(AF_INET, SOCK_STREAM, 0);
     if (sockfd < 0) 
        error("ERROR opening socket");

     portno = atoi(argv[1]);

     memset((char *) &serv_addr, 0, sizeof(serv_addr));
     serv_addr.sin_family = AF_INET;
     serv_addr.sin_addr.s_addr = INADDR_ANY;
     serv_addr.sin_port = htons(portno);

     if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(struct sockaddr)) < 0) 
              error("ERROR on binding");

     listen(sockfd, MAX_CLIENTS);

     FD_SET(sockfd, &read_fds);
     fdmax = sockfd;

     // main loop
    while (1) {
        tmp_fds = read_fds; 
        if (select(fdmax + 1, &tmp_fds, NULL, NULL, NULL) == -1) 
            error("ERROR in select");

        for(i = 0; i <= fdmax; i++) {
            if (FD_ISSET(i, &tmp_fds)) {

                if (i == sockfd) {
                    clilen = sizeof(cli_addr);
                    if ((newsockfd = accept(sockfd, (struct sockaddr *)&cli_addr, &clilen)) == -1) {
                        error("ERROR in accept");
                    } 
                    else {
                        FD_SET(newsockfd, &read_fds);
                        if (newsockfd > fdmax) { 
                            fdmax = newsockfd;
                        }
                    }
                    printf("New connection from IP %s, port %d, socket_client %d\n ", inet_ntoa(cli_addr.sin_addr), ntohs(cli_addr.sin_port), newsockfd);
                }

                else {
                    memset(buffer, 0, BUFLEN);
                    if ((n = recv(i, buffer, sizeof(buffer), 0)) <= 0) {
                        if (n == 0) {
                            printf("selectserver: socket %d hung up\n", i);
                        } else {
                            error("ERROR in recv");
                        }
                        close(i); 
                        FD_CLR(i, &read_fds);
                    } 

                    else { //recv > 0
                        printf ("I received from the client with socket %d, this message: %s\n", i, buffer);
                    }
                } 
            }
        }
     }


     close(sockfd);

     return 0; 
}

编译：
gcc client.c -o client
gcc server.c -o server

跑步（在不同的终端）：
./server 9999
./client localhost 9999