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I have a code that works fine on windows, and I have to make it compatible with Linux. Can anyone help me configure the following code snippet to windows?

    MongoDB* db = MongoDB::getInstance();
    mongocxx::pipeline p{};
    struct tm tm;
    strptime(fromdate.c_str(), "%Y-%m-%d %H %M %S", &tm); //this line gives me some errors 
    std::time_t tt = std::mktime(&tm);

The error that I'm getting `error C3861: 'strptime': identifier not found

I tried to use the code in http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/time/strptime.c?rev=HEAD but it also gives some error because it says some header files such as #include <sys/cdefs.h> , #include "namespace.h" are missing

can anyone tell me how to include those header files in the project or any other way of fixing this issue Thank you in advance

Tharindu Balasuriya
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  • Possible duplicate https://stackoverflow.com/questions/321849/strptime-equivalent-on-windows – Galik Mar 25 '21 at 08:06
  • @Galik I tried it but I get some errors when using http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/time/strptime.c?rev=HEAD as header. I wan to know the way of fixing missing headers – Tharindu Balasuriya Mar 25 '21 at 08:18
  • strptime is a POSIX function not included in current windows SDK. You need implement it by yourself or use other one's port. – Zongru Zhan Mar 25 '21 at 08:21

1 Answers1

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If you can't get the BSD version of strptime working, you could try Howard Hinnant's date.h

Or you could create a simple conversion function for this particular format yourself. Example:

#include <cstdio>
#include <ctime>
#include <cerrno>
#include <iostream>
#include <stdexcept>
#include <string>
#include <string_view>

std::tm to_tm(const std::string_view& date) {
    std::tm t{};

    if(std::sscanf(date.data(), "%d-%d-%d %d %d %d",
        &t.tm_year,
        &t.tm_mon,
        &t.tm_mday,
        &t.tm_hour,
        &t.tm_min,
        &t.tm_sec
    ) != 6)
        throw std::runtime_error("Invalid date format: " + std::string(date));

    t.tm_year -= 1900;
    --t.tm_mon;
    t.tm_isdst = -1;  // guess if DST should be in effect when calling mktime
    errno = 0;
    std::mktime(&t);
    
    return t;
}

int main() {
    std::string fromdate = "2021-03-25 08 23 56";

    std::tm x = to_tm(fromdate);

    std::cout << std::asctime(&x) << '\n'; // Thu Mar 25 08:23:56 2021
}

Or, a non-throwing version that returns std::time_t directly:

#include <system_error> // added to be able to set an error code

std::time_t to_time_t(const std::string_view& date) {
    std::tm t{};

    if(std::sscanf(date.data(), "%d-%d-%d %d %d %d",
        &t.tm_year,
        &t.tm_mon,
        &t.tm_mday,
        &t.tm_hour,
        &t.tm_min,
        &t.tm_sec
    ) != 6) {
        // EOVERFLOW (std::errc::value_too_large)
        // This is what Posix versions of mktime() uses to signal that -1 does
        // not mean one second before epoch, but that there was an error.
        errno = static_cast<int>(std::errc::value_too_large);
        return -1;
    }
    t.tm_year -= 1900;
    --t.tm_mon;
    t.tm_isdst = -1;  // guess if DST should be in effect when calling mktime
    
    errno = 0;
    return std::mktime(&t);
}
Ted Lyngmo
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