轉載：https://www.cnblogs.com/maphc/p/3462952.html

#include <iostream>
#include <time.h>
using namespace std;


time_t str_to_time_t(const string& ATime, const string& AFormat = "%d-%d-%d %d:%d:%d")
{
    struct tm tm_Temp;
    time_t time_Ret;
    try
    {
        int i = sscanf(ATime.c_str(), AFormat.c_str(),//
 
 "%d/%d/%d %d:%d:%d" ,       
            &(tm_Temp.tm_year),
            &(tm_Temp.tm_mon),
            &(tm_Temp.tm_mday),
            &(tm_Temp.tm_hour),
            &(tm_Temp.tm_min),
            &(tm_Temp.tm_sec));

        tm_Temp.tm_year -= 1900;
        tm_Temp.tm_mon
 
--;
        //如果精確到秒就把下面四行註釋掉;如果精確到天就把下面四行代碼放開
        //tm_Temp.tm_hour = 0;
        //tm_Temp.tm_min = 0;
        //tm_Temp.tm_sec = 0;
        //tm_Temp.tm_isdst = 0;
        time_Ret = mktime(&tm_Temp);
        return time_Ret;
    }
    catch (...) {
        return 0;
    }
}

time_t NowTime()
{
    time_t t_Now 
 
= time(0);
    struct tm* tm_Now = localtime(&t_Now);
    //如果精確到秒就把下面四行註釋掉;如果精確到天就把下面四行代碼放開
    //tm_Now->tm_hour = 0;
    //tm_Now->tm_min = 0;
    //tm_Now->tm_sec = 0;
    return  mktime(tm_Now);
}

bool IsValidTime(const time_t& AEndTime, const time_t& ANowTime)
{
    return (AEndTime >= ANowTime);
}


int main()
{
    string sEndTime = "2019-5-11 17:38:59";

    time_t t_Now = NowTime();
    time_t t_End = str_to_time_t(sEndTime);
    if (IsValidTime(t_End, t_Now)) {
        cout<< "有效日期" << endl;
    }
    else {
        cout << "時間過期" << endl;
    }
    return 0;
}

c++ 字符串時間格式轉換為時間 判斷有效期