c - 为什么 Connect() 返回负值？

Question

#include<io.h>
#include<stdio.h>
#include<winsock2.h>
#include <ctype.h>
#include<string.h>
#include<strings.h>

#define MY_PORT     8989 //defining the port for the socket
#define MAXBUF      256



int main(int argc , char *argv[])
{
    //char str[MAXBUF];
    int a;
    WSADATA wsa;

    SOCKET sockfd , clientfd; //SOCKET is a data type. We initialize two variables of the data type Socket here
    struct sockaddr_in self; //structure for the family,port and IP address of the socket (Socket descriptors)
    char buffer[MAXBUF]; // this is a character array that will receive the message from the client and we will use this to manipulate
    //char message[MAXBUF];
    printf("\nInitialising Winsock...");


    if (WSAStartup(MAKEWORD(2,2),&wsa) != 0) //WSASTARUP is used to tell windows to get ready for a connection and if it returns a value 0, windows is ready
    {
        printf("Failed. Error Code : %d",WSAGetLastError());
        return 1;
    }


    printf("Initialised.\n");

    /*---create streaming socket---*/
    if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0 ) //socket is created using a function called socket
                                                        //using AF_INET means that we are using TCP/IP family
                                                          //the if statement here checks whether or not the value returned by the socket is negative or not. If it is negative that means there is some sort of an error
    {
        perror("Socket");
        exit(errno);
    }
        printf("Socket created.\n");
        self.sin_family = AF_INET;
        self.sin_port = htons(MY_PORT);
        self.sin_addr.s_addr = htonl(INADDR_ANY);
        memset(&self,'\0', sizeof(self));
    /*The connect function below is used to establish a connection between the client and the server*/
    if (connect(sockfd, (struct sockaddr*)&self, sizeof(self)) <0)
        {
        printf("connection with the server failed...\n");
        exit(0);
        }
        else
        printf("connected to the server..\n");

        printf("Please enter message: ");
        memset(buffer, 0, sizeof (buffer));
        fgets(buffer, MAXBUF, stdin); //fgets is used here to get whatever is inside the buffer
        while (1)
        {
        /*struct sockaddr_in client_addr;
        int addrlen=sizeof(client_addr);*/

        /*---accept a connection (creating a data pipe)---*/

        a=  write(sockfd, buffer, sizeof(buffer));
        if(a<0){
        printf("Error");
            }
        // a= recv(clientfd, buffer, MAXBUF, 0);
        //accept(clientfd, (struct sockaddr*)&client_addr, &addrlen);

        a= read(sockfd, buffer, sizeof(buffer));
        if(a<0){
        printf("Error");
      }
        if (strncmp("QUIT", buffer, 4) == 0) {
            printf("Server Exit...\n");
            break;

        }
        }

    close(sockfd); //close the sockfd
    WSACleanup(); // windows socket is cleaned up
    return 0;
}

代码工作完全正常，但由于某种原因，我无法理解 connect 函数不断返回负值，或者至少是一个不为零的值。我与该客户端一起使用的服务器适用于其他客户端，因此我知道它没有任何问题。

我们将非常感谢您的帮助。

Answer 1

    self.sin_family = AF_INET;
    self.sin_port = htons(MY_PORT);
    self.sin_addr.s_addr = htonl(INADDR_ANY);

    memset(&self,'\0', sizeof(self));

在此代码中，您设置 self 的所有值然后你只需清除 self与 memset 。我很确定这没有任何意义，并且可能是您看到的错误的原因，即没有为 connect 给出有用的参数。 .

即使没有这个错误 memset该代码没有多大意义:您正在尝试连接到 INADDR_ANY但没有这样的IP地址可以连接。 INADDR_ANY意味着在服务器端监听机器的每个地址 - 在客户端不能使用它，而是必须使用真实的 IP 地址，例如 127.0.0.1对于本地主机。