对这个程序实在不理解啊，别人写的，读不懂，求好心大神注释下，帮说说怎么回事，非常感谢！

#include <windows.h>
#include <cstdio>
#include <process.h>
#include <stdlib.h>

#define MY_MSG WM_USER+100
const int MAX_INFO_SIZE = 20;

HANDLE hStartEvent; // thread start event
void rs232rw();
// thread function
unsigned __stdcall fun(void *param)//子线程
{
printf("子线程thread fun start\n");

MSG msg;
PeekMessage(&msg, NULL, WM_USER, WM_USER, PM_NOREMOVE);

if(!SetEvent(hStartEvent)) //set thread start event
{
printf("set start event failed,errno:%d\n",::GetLastError());
return 1;
}

while(true)
{
if(GetMessage(&msg,0,0,0)) //get msg from message queue
{
switch(msg.message)
{
case MY_MSG:
char * pInfo = (char *)msg.wParam;
printf("receive %s\n",pInfo);
printf("\n");
printf("开始执行读写txt文件任务!\n");
printf("\n");
rs232rw();
delete[] pInfo;
break;
}
}
};
return 0;
}


void rs232rw()
{FILE *fp1,*fp2,*fp3;
char c;
if((fopen("f:\\rs232.txt","r")==NULL))
{
printf("\n error on open rs232.txt!\n");
exit(0);
}
printf("正在响应执行读rs232.txt文件......\n");
printf("读取rs232.txt文件数据如下：\n");
fp1=fopen("f:\\rs232.txt","r"); /* 以读方式打开文本文件 */
while ((c=getc(fp1))!=EOF) /* 未读到文件结束标志时 */
putchar(c); /* 在显示器显示读出的字符 */
printf("\n");
fclose(fp1); /* 读文件结束，关闭文件 */
if((fopen("f:\\save232.txt","w+")==NULL))
{
printf("\n error on open save232.txt!\n");
exit(0);
}
printf("read rs232.txt successful!\n");
printf("\n");
printf("正在响应执行写save232.txt文件......\n");
fp1=fopen("f:\\rs232.txt","r"); /* 以读方式打开文本文件 */

fp2=fopen("f:\\save232.txt","w"); /* 以写方式打开文本文件 */
while ((c=getc(fp1))!=EOF)
fputc(c,fp2); /* 在显示器显示读出的字符 */
fclose(fp1);
fclose(fp2);
printf("读取save232.txt文件数据以供验证!\n");
printf("读取save232.txt文件数据如下：\n");
if((fopen("f:\\save232.txt","r")==NULL))
{
printf("\n error on open save232.txt!\n");
exit(0);
}
fp3=fopen("f:\\save232.txt","r"); /* 以读方式打开文本文件 */
while ((c=getc(fp3))!=EOF) /* 未读到文件结束标志时 */
putchar(c); /* 在显示器显示读出的字符 */
printf("\n");
fclose(fp3); /* 读文件结束，关闭文件 */

printf("write save232.txt successful!\n");
}


int main()
{
HANDLE hThread;
unsigned nThreadID;

hStartEvent = ::CreateEvent(0,FALSE,FALSE,0); //create thread start event
if(hStartEvent == 0)
{
printf("create start event failed,errno:%d\n",::GetLastError());
return 1;
}

//start thread
hThread = (HANDLE)_beginthreadex( NULL, 0, &fun, NULL, 0, &nThreadID );//创建线程
if(hThread == 0)
{
printf("start thread failed,errno:%d\n",::GetLastError());
CloseHandle(hStartEvent);
return 1;
}

//wait thread start event to avoid PostThreadMessage return errno:1444
::WaitForSingleObject(hStartEvent,INFINITE);
CloseHandle(hStartEvent);

// int count = 0;
// while(true)
//{
char* pInfo = new char[MAX_INFO_SIZE]; //create dynamic msg
sprintf(pInfo,"message!");
if(!PostThreadMessage(nThreadID,MY_MSG,(WPARAM)pInfo,0))//post thread msg
{
printf("post message failed,errno:%d\n",::GetLastError());
delete[] pInfo;
}
::Sleep(1000);
// }

CloseHandle(hThread);
return 0;
}