UDP訊息的傳送和接收需要UDP連線，所以，上面的TCP連線已經不適用了，具體的區別主要有：

建立Socket時引數不同建立服務端時不需要listen和accept操作建立客戶端時不需要connect操作伺服器需要bind操作，客戶端不需要。

傳送和接收UDP訊息要用到sendto和recvfrom兩個函式。

先來看看接收訊息，當執行recvfrom時，執行緒會進入等待，直到接收到UDP訊息為止。

// ConsoleApplication3.cpp : 定義控制檯應用程式的入口點。

//

#include "stdafx.h"

#define _WINSOCK_DEPRECATED_NO_WARNINGS    
 
//這個宣告要在stdafx.h的後面，但要在其他標頭檔案的前面

#include <winsock2.h>

#include <stdio.h>

#include <windows.h>

// 需要宣告Winsock庫

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

int _tmain(int argc, _TCHAR* argv[])

{

	int iResult = 0;

	WSADATA wsaData;



	SOCKET RecvSocket;

	sockaddr_in RecvAddr;



	unsigned
 
 short Port = 27015;



	char RecvBuf[1024];

	int BufLen = 1024;



	sockaddr_in SenderAddr;

	int SenderAddrSize = sizeof(SenderAddr);



	iResult = WSAStartup(MAKEWORD(2, 2), wsaData);

	if (iResult != NO_ERROR) {

		wprintf(L"WSAStartup failed with error %d\n", iResult);

		return 1;

	}



	RecvSocket =
 
 socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

	if (RecvSocket == INVALID_SOCKET) {

		wprintf(L"socket failed with error %d\n", WSAGetLastError());

		return 1;

	}



	RecvAddr.sin_family = AF_INET;

	RecvAddr.sin_port = htons(Port);

	RecvAddr.sin_addr.s_addr = inet_addr("127.0.0.1");



	iResult = bind(RecvSocket, (SOCKADDR *)RecvAddr, sizeof(RecvAddr));

	if (iResult != 0) {

		wprintf(L"bind failed with error %d\n", WSAGetLastError());

		return 1;

	}



	wprintf(L"Receiving datagrams...\n");

	iResult = recvfrom(RecvSocket,RecvBuf, BufLen, 0, (SOCKADDR *)&SenderAddr, &SenderAddrSize);

	if (iResult == SOCKET_ERROR) {

		wprintf(L"recvfrom failed with error %d\n", WSAGetLastError());

	}



	wprintf(L"Finished receiving. Closing socket.\n");

	iResult = closesocket(RecvSocket);

	if (iResult == SOCKET_ERROR) {

       wprintf(L"closesocket failed with error %d\n", WSAGetLastError());

       return 1;

	}



	wprintf(L"Exiting.\n");

	WSACleanup();



	return 0;

}

再來看看傳送UDP訊息

#define _WINSOCK_DEPRECATED_NO_WARNINGS //使用被棄用函式不警告,位置必須在stdafx.h的後面，在其他標頭檔案的前面

#include <winsock2.h>

#include <ws2tcpip.h>

#include <stdio.h>

// 需要宣告Winsock庫

#pragma comment(lib, "ws2_32.lib")

int wmain()

{

	int iResult;

	WSADATA wsaData;

	SOCKET SendSocket = INVALID_SOCKET;

	sockaddr_in RecvAddr;



	unsigned short Port = 27015;



	char SendBuf[1024];

	int BufLen = 1024;



	iResult = WSAStartup(MAKEWORD(2, 2),&wsaData);

	if (iResult != NO_ERROR) {

		wprintf(L"WSAStartup failed with error: %d\n", iResult);

	return 1;

	}



	SendSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

	if (SendSocket == INVALID_SOCKET) {

		wprintf(L"socket failed with error: %ld\n", WSAGetLastError());

		WSACleanup();

		return 1;

	}



	RecvAddr.sin_family = AF_INET;

	RecvAddr.sin_port = htons(Port);

	RecvAddr.sin_addr.s_addr = inet_addr("127.0.0.1");



	wprintf(L"Sending a datagram to the receiver...\n");

	iResult = sendto(SendSocket, SendBuf, BufLen, 0, (SOCKADDR *)&RecvAddr, sizeof(RecvAddr));

	if (iResult == SOCKET_ERROR) {

		wprintf(L"sendto failed with error: %d\n", WSAGetLastError());

		closesocket(SendSocket);

		WSACleanup();

	return 1;

	}



	wprintf(L"Finished sending. Closing socket.\n");

	iResult = closesocket(SendSocket);

	if (iResult == SOCKET_ERROR) {

		wprintf(L"closesocket failed with error: %d\n", WSAGetLastError());

		WSACleanup();

	return 1;

}



	wprintf(L"Exiting.\n");

	WSACleanup();



	return 0;

}