c++ 获取月初时间戳

#include<windows.h>
#include <time.h>

int GetMonthBegin(UINT iTmpStamp, UINT& iStamp)
{
　　time_t tick = static_cast<time_t>(iTmpStamp);
　　struct tm t_tm;
　　localtime_s(&t_tm, &tick);
　　t_tm.tm_mday = 1;
　　t_tm.tm_hour = 0;
　　t_tm.tm_min = 0;
　　t_tm.tm_sec = 0;
　　iStamp = static_cast<UINT>(mktime(&t_tm));
　　return TRUE;
}