Winsock 学习笔记（二）Winsock Client Application

As for Why do Microsoft code samples tend to use ZeroMemory instead of ={ 0 }? 
Are there any differences? 
You can search it on baidu.
But I recommend to visit a discussion post on msdn: http://blogs.msdn.com/b/oldnewthing/archive/2005/06/28/433341.aspx
Since I find that all the searching results on baidu are slightly different.
However, after having a quick browsing on the discussion post, I get more than I've expected.
Maybe one not well-known feature is as follow:
Sayeth K&R:"Unnamed bit-field members are ignored, and are not initialized.";  Zero memory is going to clear all of the bitfields in your struct, but the ={0} technique does not.

By the way, do not use ZeroMemory() or memset() for your C++ structures that contain objects as structure members; that may corrupt their internal state and be the reason for a crash.

#ifndef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#endif

#include <Windows.h>
#include <WinSock2.h>
#include <WS2tcpip.h>
#include <IPHlpApi.h>
#include <stdio.h>

#pragma comment(lib, "Ws2_32.lib")

#define DEFAULT_PORT "27015"//define the port on server by default which the client will connect to
#define DEFAULT_BUFLEN 512

int main(int argc, char *argv[]){
	WSADATA wsaData;

	int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
	if (iResult != 0){
		printf("WSAStartup failed: %d\n", iResult);
		return 1;
	}

	struct addrinfo *result = NULL,
		*ptr = NULL,
		hints;//Declare an addrinfo object that contains a sockaddr structure and initialize these values. For details of this struct, just check msdn

	ZeroMemory(&hints, sizeof(hints));//just a macro definition of memset.
	//Do not use ZeroMemory() or memset() for your C++ structures that contain objects as structure members; 
	//that may corrupt their internal state and be the reason for a crash.

	hints.ai_family = AF_UNSPEC;//Unspecify the Internet address family so that either IPv4 or IPv6 can be returned.
	hints.ai_socktype = SOCK_STREAM;//specify the socket type to be stream
	hints.ai_protocol = IPPROTO_TCP;//use TCP protocol

	//requesting the IP address for the server name passed on the command line stored in "result"
	iResult = getaddrinfo(argv[1], DEFAULT_PORT, &hints, &result);
	if (iResult != 0){ //check for errors
		printf("getaddrinfo failed: %d\n", iResult);
		WSACleanup();//WSACleanup is used to terminate the use of the WS2_32 DLL.
		return 1;
	}

	SOCKET ConnectSocket = INVALID_SOCKET;//Create a SOCKET object

	// Attempt to connect to the first address returned by
	// the call to getaddrinfo
	ptr = result;
	//creates a socket that is bound to a specific transport service provider
	ConnectSocket = socket(ptr->ai_family, ptr->ai_socktype, ptr->ai_protocol);

	//If the socket call fails, it returns INVALID_SOCKET.
	if (ConnectSocket == INVALID_SOCKET){
		//WSAGetLastError returns an error number associated with the last error that occurred.
		printf("Error at socket(): %ld\n", WSAGetLastError());
		freeaddrinfo(result);
		WSACleanup();
		return 1;
	}

	//Connect to server provided with the created socket and the sockdaddr structure
	iResult = connect(ConnectSocket, ptr->ai_addr, (int)ptr->ai_addrlen);
	if (iResult == SOCKET_ERROR){
		closesocket(ConnectSocket);
		ConnectSocket = INVALID_SOCKET;
	}

	// Should really try the next address
	//(Why? Be sure that "result" is a  pointer to a linked list of one or more addrinfo structures) 
	//returned by getaddrinfo
	// if the connect call failed
	// But for this simple example we just free the resources
	// returned by getaddrinfo and print an error message

	freeaddrinfo(result);

	if (ConnectSocket == INVALID_SOCKET){
		printf("Unable to connect to server!\n");
		WSACleanup();
		return 1;
	}

	int recvbuflen = DEFAULT_BUFLEN;

	char *sendbuf = "this is a test";
	char recvbuf[DEFAULT_BUFLEN];

	//The send and recv functions both return an integer value of the number of bytes sent or received, respectively, 
	//or an error.Each function also takes the same parameters : the active socket, 
	//a char buffer, the number of bytes to send or receive, and any flags to use.
	iResult = send(ConnectSocket, sendbuf, (int)strlen(sendbuf), 0);
	if (iResult == SOCKET_ERROR){
		printf("send failed: %d\n", WSAGetLastError());
		closesocket(ConnectSocket);
		WSACleanup();
		return 1;
	}

	printf("Bytes Sent: %ld\n", iResult);

	// shutdown the connection for sending since no more data will be sent
	// the client can still use the ConnectSocket for receiving data
	iResult = shutdown(ConnectSocket, SD_SEND);
	if (iResult == SOCKET_ERROR){
		printf("shutdown failed: %d\n", WSAGetLastError());
		closesocket(ConnectSocket);
		WSACleanup();
		return 1;
	}

	// Receive data until the server closes the connection
	do{
		iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);
		if (iResult > 0)
			printf("Bytes received: %d\n", iResult);
		else if (iResult == 0)
			printf("Connection closed\n");
		else
			printf("recv failed: %d\n", WSAGetLastError());
	} while (iResult > 0);

	//cleanup
	closesocket(ConnectSocket);
	WSACleanup();

	return 0;
}