convert data/time to tm/time_point against musl and glibc. Common way

Question

I would like to convert string data to struct tm (c) or std::chrono::time_point. The problem is I wanna working solution for both standard libc (glibc and musl). I have tree standard formats that I wanna parse.

1. RFC-1123

   Sun, 06 Nov 1994 08:49:37 GMT

2. RFC-850

   "Sunday, 06-Nov-94 08:49:37 GMT"

3. ANSI C's asctime format

   Sun Nov 6 08:49:37 1994"

Is there any way to make it work? std::get_time has a bug
strptime work fine (and quick) on glibc but fail against musl.

Any idea? I don't wanna use stream like in get_time. But If it would be necessary that fine. (It's ok to use GCC5> and c++11 standard)

Answer 1

Howard Hinnant's free, open source, header-only, date/time library can parse these formats into a std::chrono::time_point, even in the context of faulty get_time and strptime facilities. It does require the use of std::istringstream though. Here is what it looks like:

#include "date.h"
#include <sstream>

std::chrono::system_clock::time_point
parse_RFC_1123(const std::string& s)
{
    std::istringstream in{s};
    std::chrono::system_clock::time_point tp;
    in >> date::parse("%a, %d %b %Y %T %Z", tp);
    return tp;
}

std::chrono::system_clock::time_point
parse_RFC_850(const std::string& s)
{
    std::istringstream in{s};
    std::chrono::system_clock::time_point tp;
    in >> date::parse("%a, %d-%b-%y %T %Z", tp);
    return tp;
}

std::chrono::system_clock::time_point
parse_asctime(const std::string& s)
{
    std::istringstream in{s};
    std::chrono::system_clock::time_point tp;
    in >> date::parse("%a %b %d %T %Y", tp);
    return tp;
}

This can be exercised like this:

#include <iostream>

int
main()
{
    auto tp = parse_RFC_1123("Sun, 06 Nov 1994 08:49:37 GMT");
    using namespace date;
    std::cout << tp << '\n';
    tp = parse_RFC_850("Sunday, 06-Nov-94 08:49:37 GMT");
    std::cout << tp << '\n';
    tp = parse_asctime("Sun Nov 6 08:49:37 1994");
    std::cout << tp << '\n';
}

and outputs:

1994-11-06 08:49:37.000000
1994-11-06 08:49:37.000000
1994-11-06 08:49:37.000000

The parse flags %a and %b are normally locale-dependent. However if you compile this library with -DONLY_C_LOCALE=1 it becomes locale independent. It should give the same result either way. But from a practical standpoint, if you compile without -DONLY_C_LOCALE=1 and you don't get the results above, you have to submit a bug report to your std::lib vendor.

If you compile with -DONLY_C_LOCALE=1 and you don't get the results above, rattle my cage, and I will have it fixed within days, if not hours.