我用C++为Unix(TCP(制作了一个服务器套接字，它只接受一个客户端套接字。今天，我试图让它接受多个。出于某种原因，它最终只接受1，并且没有接收到能够连接的客户端发送的消息。我认为选择功能无法正常工作。仅供参考：我是套接字编程的新手，所以请理解这是否是一个愚蠢的错误。
这是代码：
#include <iostream>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <cstring>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/select.h>
#define PORT 8080
#define MAXCLIENTS 30
int main()
{
//create a socket
int listening = socket(AF_INET, SOCK_STREAM, 0); //(returns int) - makes socket (returns what socket it is in terms of an int)
if(listening < 0) //check if we were able to make a socket!
{
std::cerr << "Can't create socket!" << std::endl;
return -1;
}
//bind the socket to an IP/Port
sockaddr_in hint{}; // This creates a structure for the ipv4 info of the socket.
hint.sin_family = AF_INET; //set the family to ipv4
hint.sin_port = htons(PORT); //set the port to the macro set above (use host-to-network-short to conver the int to the port)
hint.sin_addr.s_addr = INADDR_ANY; //set the ip to any address
if(bind(listening, (sockaddr*)&hint, sizeof(hint)) < 0) //attempt to bind socket (inticated by what number the `listening` socket is) to ip/port
{
std::cerr << "Can't bind to IP/Port" << std::endl;
return -1;
}
//mark the socket for listening
if(listen(listening, MAXCLIENTS) < 0 /*SOMAXCONN = maximum amount of connections, defined by sys/socket.h*/) //attempt to listen on the socket number indicated by `listening`
{
std::cerr << "Can't listen on the socket!" << std::endl;
return -1;
}
//FD_CLR() = Remove 1 from set
//FD_SET() = Add to set
//FD_ZERO() = Remove everything from set
//FD_ISSET() = Check if something is part of a set
fd_set master; //define the set
int max_sd;
int client_socks[MAXCLIENTS]{};
while (true)
{
FD_ZERO(&master); //make sure it's cleared
FD_SET(listening, &master); //add the listening socket (server) to the set
max_sd = listening; //max socket descriptor set to the listening socket (need this for the select func)
for (int i = 0; i < MAXCLIENTS; i++) {
if (client_socks[i] > 0) //make sure the particular socket exists
{
FD_SET(client_socks[i], &master); //add it to the set
}
if (client_socks[i] > max_sd) //if the socket is greater than our current maximum socket descriptor
{
max_sd = client_socks[i];
}
}
//wait for some action on any socket within the master fd (this will set the master fd_set to be equal to whatever socket had some action on it)
int activity = select(max_sd + 1, &master, nullptr, nullptr, nullptr);
if (activity < 0) //error!
{
std::cerr << "Error while trying to select!" << std::endl;
}
int addrlen = sizeof(hint);
if (FD_ISSET(listening, &master)) //if the select got that there was action on the listening (server) socket - most likely, a client socket is trying to connect!
{
int client_socket;
client_socket = accept(listening, (sockaddr *) &hint, &addrlen); //accept the first client "waiting to get in"
if (client_socket < 0) {
std::cerr << "Something went wrong when trying to accept a client socket!" << std::endl;
break;
}
std::cout << "New connection: " << inet_ntoa(hint.sin_addr) << " on port " << ntohs(hint.sin_port) << std::endl;
if (send(client_socket, "Welcome to the socket party!", strlen("Welcome to the socket party!"), 0) != strlen("Welcome to the socket party!")) { //greetings!
std::cerr << "Error when sending welcome message." << std::endl; //something went wrong ;(
}
for (int i = 0; i < MAXCLIENTS; i++) //for each index, set client_sock to the address of the index of client_socks, so that we can set the value of it!
{
if(client_socks[i] == 0) //if this position is null (0)
{
client_socks[i] = client_socket;
}
}
}
//else, there was action on a client socket (most likely a message is being sent!
char buffer[2048]; //we need somewhere to store clients messages!
for (int &client_sock : client_socks) //loop through the client sockets
{
if (client_sock != 0)
{
if (FD_ISSET(client_sock, &master) == 0) //check if the select got action on the particular index in the client_socks array
{
memset(&buffer, 0, sizeof(buffer)); //make sure the buffer is clear!
if (read(client_sock, &buffer, 2048) == 0) //check if nothing was recieved from the client
{
getpeername(client_sock, (sockaddr*)&hint, (socklen_t*)&addrlen) < 0; //gets networking info, based off of which socket is passed (the if statement checks for errors). In addition, it sets the values of hint to the info from the passed socket
//print that the client disconnected
std::cout << "A client has disconnected! IP: " << inet_ntoa(hint.sin_addr) << " Port: " << ntohs(hint.sin_port) << std::endl;
close(client_sock); //close the socket
client_sock = 0; //set its value in the array to 0, so that we can reuse it!
}
//else, we got message from the client
for (int &socket : client_socks)
//if (socket != client_sock)
send(socket , buffer , strlen(buffer) , 0 );
}
}
}
return 0;
}
}
您的client_socks变量必须初始化，正如Igor所说-只需附加大括号：int client_socks[MAXCLIENTS]{};。
那么您的for (int &client_sock : client_socks)循环不会忽略0个值(您显然希望在给定"if(client_socks[i] == 0) //if this position is null (0)"的情况下将其作为一个哨兵(。在该循环中，添加"；如果(client_sock[i]==0(继续；. Because you try to从描述符0读取`，它将阻止等待键盘输入。
此外，如果你希望你的代码是健壮的，你会使侦听套接字不阻塞，因为该套接字可以选择可读的，但当你的应用程序从中接受时，客户端连接尝试已经被放弃：然后你会阻塞等待接受另一个可能永远不会到来的客户端连接尝试，并且不为现有客户端提供服务。