winsock select()ing 运行时错误

Posted 2023-02-22

【中文标题】winsock select()ing 运行时错误

【英文标题】：winsock select()ing runtime error

【发布时间】：2010-11-29 07:46:36

【问题描述】：

我正在尝试解决我之前发布的关于同步聊天消息的问题，一位成员向我指出了 select() 函数的方向。我阅读了 Beej 网络指南下的this 部分，并尝试编写在 windows 下给出的示例。它编译得很好，但是当我去测试它时，在将端口号输入程序后，程序崩溃并显示我的错误消息"-Select error"-。我不确定如何让这个工作，请指教。

服务器.cpp

#include <iostream>
#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
using namespace std;
const int winsockver = 2;
int PORT;
int fdmax;
char buffer[80];

int main(void)
    //*********************************************
    fd_set master;
    fd_set temp;
    SOCKET newfd;
    struct sockaddr_in connected_client;
    //*********************************************

    WSADATA wsadata;
    if (WSAStartup(MAKEWORD(winsockver,0),&wsadata) == 0 )
        cout<<"-Winsock Initialized." << endl;
        cout<<"Enter PORT:";
        cin>> PORT;
        //--------------------------------------------------------------------
        struct sockaddr_in server_info;
        server_info.sin_family = AF_INET;
        server_info.sin_port = htons(PORT);
        server_info.sin_addr.s_addr = INADDR_ANY;

        SOCKET serv_sock = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
        if ( serv_sock != INVALID_SOCKET)
            if ( bind(serv_sock,(sockaddr*)&server_info,sizeof(server_info)) != -1 )
                char yes = '1';
                if ( setsockopt(serv_sock,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(yes)) != SOCKET_ERROR)
                    cout<<"-Binding Successful." << endl;
                
            

            if ( listen(serv_sock,5) != -1 )
                cout<<"-Listening for incoming connections." << endl;
            

            FD_SET(serv_sock,&master);
            fdmax = serv_sock; // keeping track of the largers sockfd, at this moment its serv_sock
            //#########################################################
            for(;;)
                temp = master; // copying to temp the master set
                if (select(fdmax+1,&temp,NULL,NULL,NULL) == -1 )
                    cout<<"-select error." << endl;
                

                //run through existing connections looking for data to read 
                for (int i = 0; i <= fdmax; i++)
                    if (FD_ISSET(i,&temp))//we have one
                        if (i == serv_sock)//handle new connections
                            int size =sizeof(connected_client);
                            newfd = accept(serv_sock,(sockaddr*)&connected_client,&size);

                            if ( newfd == -1 )
                                cout<<"-Accepted an invalid socket from newfd." << endl;
                            else//accept has returned a valid socket descriptor and we add it to the master
                                FD_SET(newfd,&master);
                                if (newfd > fdmax )
                                    fdmax = newfd;
                                
                                char *connected_ip= inet_ntoa(connected_client.sin_addr);   
                                cout<<"-Select server new connection from " << connected_ip << " " <<  endl;
                            

                        else
                            //handle data from a client
                            int bytes_in;
                            bytes_in = recv(i,buffer,sizeof(buffer),0);
                            if ( bytes_in <= 0 )
                                if (bytes_in == 0 )
                                    cout<<"-Connected socket " << i << ",disconnected " << endl;
                                else
                                    cout<<"-Socket error." << endl;
                                
                                closesocket(i);
                                FD_CLR(i,&master); //remove from master set.
                            else
                                //we get data from a client
                                for (int j=0; j <= fdmax; j++ )
                                    //send to everyone
                                    if (FD_ISSET(j,&master))
                                        //except the listener and ourself
                                        if ( (j != serv_sock) && (j != i) )
                                            if ( send(j,buffer,sizeof(buffer),0) == -1 )
                                                cout<<"-Sending error" << endl;
                                            
                                        
                                    
                                
                            
                        
                    
                
            
            //#########################################################
        

        //--------------------------------------------------------------------
    else
        cout<<"-Unable to Initialize." << endl;
    

    if ( WSACleanup() != -1 )
        cout<<"-Cleanup Successful." << endl;
    
    return 0;

【问题讨论】：

只是一个提示：不要检查 select() 返回值是否与 -1 相比，而是与 SOCKET_ERROR 相比。一旦出现错误，显示WSAGetLastError() 结果。

干杯西蒙娜`

【参考方案1】：

您的文件描述符集未正确初始化，因此当您对其调用FD_SET() 时，它们仍然包含垃圾。

您应该在开始使用它们之前调用FD_ZERO() 来初始化它们：

FD_ZERO(&master);
FD_SET(serv_sock, &master);
fdmax = serv_sock;

【讨论】：

我没想到，这就是 Frederic 的原因。再次感谢您。