实现UDP协议，socket编程，调用到windowsAPI，实现客户端和服务器

#include <stdio.h>
#include <stdlib.h>
#include <winsock2.h>

int main()
{
WSADATA wsaData;
SOCKET RecvSocket;
struct sockaddr_in RecvAddr;
int port = 27015;
char RecvBuf[1024];
int BufLen = 1024;
int len =0;
int flag = 0;
FILE* fp;
struct sockaddr_in SenderAddr;
int SenderAddrSize = sizeof(SenderAddr);
//
WSAStartup(MAKEWORD(2, 2), &wsaData);

RecvSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

RecvAddr.sin_family = AF_INET;
RecvAddr.sin_port = htons(port);
RecvAddr.sin_addr.s_addr = htonl(INADDR_ANY);
// 用于多方面数据的接受，符合服务器的数据传输的模式
if(bind(RecvSocket, (SOCKADDR* )&RecvAddr, sizeof(RecvAddr))< 0){
printf("Error: bind failed!\n");
exit(1);
}
printf("Receving datagrams ... \n");

for(; ; ){
static int count = 0;
static int fileNum = 0;
char filenameTmp[20];
len = recvfrom(RecvSocket, RecvBuf, BufLen, 0, (SOCKADDR* )&SenderAddr, &SenderAddrSize);
sendto(RecvSocket, RecvBuf, BufLen, 0, (SOCKADDR* )&SenderAddr, &SenderAddrSize);
//printf("Data Success, and sended!");
RecvBuf[len] = '\0';
//  此处的判断是为了文件接收的转换的情况， 注意加强自身的对UDP 协议的理解；
if(strcmp(RecvBuf, "file send -- 123")==0){
fileNum++;
sprintf(filenameTmp, "receive%d.txt", fileNum);
fp = fopen(filenameTmp, "a+");
printf("file will received\n");
flag = 1;
}else if(strcmp(RecvBuf, "file sended -- 123")==0){
printf("file have received!\n");
fclose(fp);
flag = 0;
}else{
if(flag == 1){
count++;
fprintf(fp ,"%s\t",RecvBuf);
if((count%5)== 0){
fprintf(fp ,"\n");
}

}else{
printf("Received Data: %s\n", RecvBuf);
}

}

}

printf("Finished receiving. Closing socket. \n");
closesocket(RecvSocket); // 销毁套接字， 逻辑严密性

printf("Exiting.\n");
return 0;
}