c - 接受的套接字上的“错误文件描述符”错误

Question

我正在尝试进入网络编程，并且一直在遵循套接字的指南。我用C语言编写了一个简单的Windows TCP服务器和客户端，但似乎无法使它们正常工作。客户端连接的第二秒，服务器将引发“错误文件描述符”错误并关闭。我不明白accept()刚创建的文件描述符可能是不好的。我对此进行了研究，只发现在阅读文件之前已关闭文件的人，而我没有。

这是代码:

服务器

#include <stdio.h>
#include <stdlib.h>
#include <winsock2.h>

int main(int argc, char *argv[])
{
    WSADATA WSAData;
    WSAStartup(MAKEWORD(2,0), &WSAData);

    SOCKET sock, newsock;
    int portno, clilen;
    char buffer[256];
    SOCKADDR_IN serv_addr, cli_addr;
    int n;

    sock = socket(AF_INET, SOCK_STREAM, 0);

    if (sock < 0)
    {
        perror("Error opening socket");
        exit(1);
    }

    memset((char *) &serv_addr, 0, sizeof(serv_addr));
    portno = 5001;

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = INADDR_ANY;
    serv_addr.sin_port = htons(portno);

    if (bind(sock, (SOCKADDR *) &serv_addr, sizeof(serv_addr)) < 0)
    {
        perror("Eror on binding");
        exit(1);
    }

    listen(sock, 5);
    clilen = sizeof(cli_addr);

    newsock = accept(sock, (SOCKADDR *) &cli_addr, &clilen);
    if (newsock < 0)
    {
        perror("Error on accept");
        exit(1);
    }

    memset(buffer, 0, 256);
    n = read(newsock, buffer, 255);

    if (n < 0)
    {
        perror("Error reading from socket");
        exit(1);
    }

    printf("Here is the message : %s\n", buffer);

    n = write(newsock, "I got your message", 18);
    if (n < 0) 
    {
        perror("Error writing to socket");
        exit(1);
    }

    WSACleanup();
    return 0;
}

客户

#include <stdio.h>
#include <stdlib.h>
#include <winsock2.h>

int main(int argc, char *argv[])
{
    WSADATA WSAData;
    WSAStartup(MAKEWORD(2,0), &WSAData);

    SOCKET sock;
    int portno, n;
    SOCKADDR_IN serv_addr;
    HOSTENT *server;
    char buffer[256];

    if (argc < 3)
    {
        fprintf(stderr, "Usage : %s hostname port\n", argv[0]);
        exit(0);
    }

    portno = atoi(argv[2]);
    sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock < 0)
    {
        perror("Error opening socket\n");
        exit(1);
    }

    server = gethostbyname(argv[1]);

    if (server == NULL)
    {
        perror("Error, no such host");
        exit(1);
    }

    memset((char *) &serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    memcpy((char *) &serv_addr.sin_addr.s_addr, (char *) server->h_addr, server->h_length);
    serv_addr.sin_port = htons(portno);

    if (connect(sock, (SOCKADDR *) &serv_addr, sizeof(serv_addr)) < 0)
    {
        perror("Error connecting to server");
        exit(1);
    }

    printf("Please enter your message : ");
    memset(buffer, 0, 256);
    fgets(buffer, 255, stdin);

    n = write(sock, buffer, strlen(buffer));
    if (n < 0)
    {
        perror("Error writing to socket");
        exit(1);
    }

    memset(buffer, 0, 256);
    n = read(sock, buffer, 255);

    if (n < 0)
    {
        perror("Error reading from socket");
        exit(1);
    }

    printf("%s\n", buffer);

    WSACleanup();
    return 0;
}

...这是输出，以防万一:

C:\...myfolder>server
*here it does nothing until I start the client with "client 127.0.0.1 5001" in another window*
Error reading from socket: Bad file descriptor

您看到我的代码有什么问题吗？在此先感谢您的帮助!

Answer 1

我会将其放在注释中，但是尝试使用recv()函数而不是read()。这是因为read()不会调用Socket API，因此就Windows而言，文件描述符无效。

同样，在客户端中，应使用send()而不是write()。