Link error when HAS_STRING_VIEW is defined

[DorfilIkatu]

Hi,

I was trying to build an example using libtz.so, and I got an "undefined reference" error.

Following is the code of my example:

#include <iostream>
#include "date/date.h"
#include "date/tz.h"

using namespace std;
using namespace date;

int main()
{
    auto t = make_zoned("Europe/London", chrono::system_clock::now());
    cout << t << endl;
   return 0;
}

The link error:

 "[...] undefined reference to `date::locate_zone(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'"

When I run nm command on libtz.so to check that locate_zone symbol was there, I got:

0001198c T date::locate_zone(std::basic_string_view<char, std::char_traits<char> >)
000081fc T date::tzdb::locate_zone(std::basic_string_view<char, std::char_traits<char> >) const 

The result I got indicates that the library was compiled with HAS_STRING_VIEW=1, while the linker was trying to find the function version that is built when HAS_STRING_VIEW=0.

After this I set HAS_STRING_VIEW=0 and built everything again, and this time the build was successful.

I'm not calling locate_zone directly, it is being called inside the library itself so, is it possible that this is a bug of the library and not an error on my example?

Thanks

[HowardHinnant]

It may be a cmake bug, but I am not sure. I am not fluent in cmake and don't use it for myself. Others are maintaining it. I just always include src/tz.cpp in my build and don't bother making it into a separate library, and so my flags don't have an opportunity to differ between tz.cpp and the clients of tz.cpp.

[lkolda]

This should not be an excuse to provide a working version. I can not use it because it can't be added as DorfilIkatu said.

[emptyVoid]

I'm facing the same issue with vcpkg as the package manager on Windows. For date it does not set CMAKE_CXX_STANDARD, and VC++ 2019 defaults to C++14, while my code is compiled under C++17.

In my opinion the API should at least be backward-compatible, proving const time_zone* locate_zone(const std::string& tz_name); under C++17 too. Or even better -- the internal API could be in plain C.

[degski]

This is still a problem, compiling with C++17 results in locate_zone undefined linking errors (on Windows). Compiling the .cpp file into the project is not a good solution.

EDIT: I've opened #7591 on vcpkg and added a quick fix, the port is simply in-complete.