Is this how you use select()?

[Clipster]

I found out how to use the select() function, or at least I think I have. It allows the loop to keep going and then receive something when there is something to receive.

Here's the Server:

// main.cpp
#ifndef WIN32
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netdb.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#define SOCKET int
#endif
#ifdef WIN32
#include <winsock2.h>
#include <iostream>
#include <io.h>
#pragma comment (lib,"ws2_32")
#endif

int main()
{
	WORD			SocketVersion;
	WSADATA			WsaData;
	int				WsaErr;
	int				recvBytes(0);
	char			Buffer[5000];
	bool			InternalError(false);
	bool			ActiveAccept(true);
	bool			ActiveApp(true);
	char*			ip_address = NULL;
	fd_set			FD_SET1;
	struct timeval  timeOUT;
	timeOUT.tv_sec  = 0;
	timeOUT.tv_usec = 0;

	FD_ZERO (&FD_SET1);

	SocketVersion = MAKEWORD(2, 2);
	WsaErr = WSAStartup(SocketVersion, &WsaData);

	std::cout << "\n";

	if(WsaErr == 0)
	{
		if(LOBYTE(WsaData.wVersion) == 2 || HIBYTE(WsaData.wVersion) == 2)
		{
			SOCKET My_Socket;
			My_Socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

			if(My_Socket != INVALID_SOCKET)
			{
				sockaddr_in Server;
				Server.sin_family		 = AF_INET;
				Server.sin_addr.s_addr	 = (!ip_address) ? INADDR_ANY:inet_addr(ip_address);
				Server.sin_port			 = htons(55555);

				if(bind(My_Socket, (SOCKADDR*)&Server, sizeof(Server)) != SOCKET_ERROR)
				{
					if(listen(My_Socket, 1) != SOCKET_ERROR)
					{
						SOCKET AcceptConnection;
						AcceptConnection = SOCKET_ERROR;
						
						std::cout << " Server: The Server Has Been Started Up Successfully!\n";
						
						while(ActiveAccept == true)
						{
							AcceptConnection = accept(My_Socket, NULL, NULL);
							if(AcceptConnection != SOCKET_ERROR)
							{
								ActiveAccept = false;
							}
						}
						
						int ClientConnected = 1;
						My_Socket = AcceptConnection;

						//######## MAIN LOOP
						while(ActiveApp == true)
						{
							FD_ZERO(&FD_SET1);
							FD_SET(My_Socket, &FD_SET1);

							if(ClientConnected == 1)
							{
								std::cout << " Server: Client Connected!\n";
								ClientConnected = 0;
							}
							//######## START SEND RECEIVE HERE
							if(select((int)My_Socket, &FD_SET1, 0, 0, &timeOUT))
							{
								recvBytes = recv(My_Socket, Buffer, 5000, 0);
								if(recvBytes != SOCKET_ERROR)
								{
									std::cout << " Server->Message: " << Buffer << "\n";
								}
								else
								{
									if(WSAGetLastError() == 10054)
									{
										std::cout << " Server: Client Disconnected.\n";
										ActiveApp = false;
										InternalError = true;
									}
								}
							}
						}
					}
					else
					{
						std::cout << " Server: " << WSAGetLastError() << "\n";
						InternalError = true;
					}
				}
				else
				{
					std::cout << " Server: " << WSAGetLastError() << "\n";
					InternalError = true;
				}
			}
			else
			{
				std::cout << " Server: " << WSAGetLastError() << "\n";
				InternalError = true;
			}
		}
		else
		{
			std::cout << " Server: The DLL in use does not support this version of WinSock!\n";
			InternalError = true;
		}
	}
	else
	{
		std::cout << " Server: There was an error starting WinSock!\n";
		InternalError = true;
	}

	// Internal Error Loop
	if(InternalError == true)
	{
		for(int InternErr = 0;InternErr < 3;InternErr++)
		{
			if(InternErr == 1)
			{
				std::cout << "\n Closing...\n";
			}
			Sleep(1000);
		}
	}
}

Client:

// main.cpp
#ifndef WIN32
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netdb.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#define SOCKET int
#endif
#ifdef WIN32
#include <winsock2.h>
#include <iostream>
#include <string>
#pragma comment (lib,"ws2_32")
#endif

int main()
{
	WSADATA			WsaData;
	WORD			SocketVersion;
	int				SocketCreate;
	bool			InternalError(false);

	SocketVersion = MAKEWORD(2, 2);
	SocketCreate = WSAStartup(SocketVersion, &WsaData);

	std::cout << "\n";

	if(SocketCreate == NO_ERROR)
	{
		SOCKET My_Socket;
		My_Socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
		if(My_Socket != INVALID_SOCKET)
		{
			sockaddr_in Client;
			Client.sin_family		= AF_INET;
			Client.sin_addr.s_addr	= inet_addr("127.0.0.1");
			Client.sin_port			= htons(55555);

			if(connect(My_Socket, (SOCKADDR*)&Client, sizeof(Client)) != SOCKET_ERROR)
			{
				//######## MAIN LOOP
				while(1)
				{
					//######## START SEND RECEIVE HERE
					static std::string Message;

					std::cout << " Client->Type A Message To Send To Server: ";
					getline(std::cin, Message);
					
					if(Message != "")
					{
						if(send(My_Socket, Message.c_str(), 5000, 0) != SOCKET_ERROR)
						{
							std::cout << " Client: Message Sent!!!\n";
							Message = "";
						}
					}
				}
			}
			else
			{
				std::cout << " Client: Faild To Connect To Server!!!\n";
				InternalError = true;
			}
		}
		else
		{
			std::cout << " Client: " << WSAGetLastError() << "\n";
			InternalError = true;
		}
	}
	else
	{
		std::cout << " Client: There was an error on WSAStartup()!!!\n";
		InternalError = true;
	}

	// Internal Error Loop
	if(InternalError == true)
	{
		for(int InternErr = 0;InternErr < 3;InternErr++)
		{
			if(InternErr == 1)
			{
				std::cout << "\n Closing...\n";
			}
			Sleep(1000);
		}
	}
}

Everything seems to go fine if I connect to the server though my local ip address.
But when I connect though my public IP address things go weird.
I can connect and everything. The problem is that when I send some data it also sends some other data, which seems to be null. This does not happen when I connect though 127.0.0.1.
And it does not happen if I remove select() regardless of the IP.

Like if I send the string "Hello World!" without the select function I will get:

 Server->Message: Hello World!

With the select function I will get:

Server->Message: Hello World!
Server->Message:
Server->Message:

Or:

Server->Message: Hello World!
Server->Message:

The amount of "Null"s change. Sometimes there's 3, then maybe 2, 4 etc.
This is really annoying me because I have no idea whats causing this.

Thanks for any help that I may get!

[Richard.J]

assuming you're using Windows, the first parameter of select should be 0 because on Windows, it is ignored.
Then, you should not call recv() on MySocket, because that is the server socket used for establishing connections.

You don't need
while(ActiveAccept == true)
because accept() will block unless you have set your server socket to nonblocking (which you don't have, as far as I can see.

You should put AcceptConnection into FD_SET1 and when select returns, first check the error condition (as you do), then test with FD_ISSET if your socket is ready for reading (select can handle more than 1 socket).
And as you set your timeout to 0, select() might return immediately (I'm not sure). If you want to wait forever, pass 0 as last parameter.

HTH,
Richard