Stack around the variable is corrupted

void myInvalidParameterHandler(const wchar_t* expression,
   const wchar_t* function, 
   const wchar_t* file, 
   unsigned int line, 
   uintptr_t pReserved)
{
	wprintf(L"Invalid parameter detected in function %s."
            L" File: %s Line: %d\n", function, file, line);
   wprintf(L"Expression: %s\n", expression);

   
}


void main()
{
	struct tm when;
	int yy=00, mm=00,dd=00;
	char date[20];
	errno_t errNo;
	strcpy(date,"2010-05-03");
	sscanf_s(date,"%4d-%2d-%2d",&yy,&mm,&dd);
	printf("year : %4d\n",yy);
	printf("month : %2d\n",mm);
	printf("date : %2d\n",dd);

	when.tm_year = yy - 1900;
	when.tm_mon = mm - 1;
	when.tm_mday = dd;
	when.tm_hour = 0;
	when.tm_min = 0;
	when.tm_sec = 0;
	when.tm_wday = 0;
	
	_invalid_parameter_handler oldHandler, newHandler;
	newHandler = myInvalidParameterHandler;
	oldHandler = _set_invalid_parameter_handler(newHandler);
	_CrtSetReportMode(_CRT_ASSERT , 0);
	errNo = asctime_s(date,32,&when);
	printf("date is right...\n");

}