Template instantiation

[jcoupey]

First of all many thanks for providing this useful C++ implementation!

This is more of a question/comment than a real issue: I'm trying to use the code as a dependency in my project and my own code compiles just fine when building and including polylineencoder.h. But then I'm experiencing errors for all of the used functions at linking stage, e.g.

 undefined reference to `gepaf::PolylineEncoder<6>::decode(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'

I solved this by explicitly forcing the instantiation for precision values I need. Adding at the end of polylineencoder.cpp:

template class PolylineEncoder<5>;
template class PolylineEncoder<6>;

Is this the expected way to use the project from elsewhere? If so, maybe it would be worth mentioning in the README.

[vahancho]

Hi,

How do you use Pololineencoder? Do you build it as a library and link your application to it, or you build polylineencoder.cpp as a part of your project?

UPD:

The error you see indicates a missing symbol. It might be that you don't build the corresponding .cpp file that contains the function definitions.

[jcoupey]

I simply build polylineencoder.cpp as part of my project (added it to an existing list of cpp files in my makefile) and then include polylineencoder.h where I need it.

All compilations steps are OK, only the linking fails. It makes sense because when building my client file the compiler has an incomplete view of the PolylineEncoder class so it expects to find actual implementation in another object during linking. And upon building polylineencoder.cpp there is no explicit instantiation of PolylineEncoder<5> or PolylineEncoder<6>.

[vahancho]

Ah, I see. The problem is that Polylineencoder is a class template and the member functions should be defined in the header file instead of source file. That explains the errors you get. I haven't noticed the problem with the unit tests because they have the following statement:

#include "polylineencoder.cpp"

Ok, thank you for reporting this. I will take care of it.

[jcoupey]

the member functions should be defined in the header file instead of source file

That would solve the problem with the additional advantage of making it easier to include as header-only from the point of view of a downstream project.

[jcoupey]

Thanks for the quick fix! Just reporting that I updated with the header-only version and it works fine. 👍

[vahancho]

Hi Julien,

Thank you once more for reporting this issue and confirming the fix. I hope the code will work good for your project.

Cheers,
Vahan

[jcoupey]

Thanks again for the fix. FYI, the purpose on my side is to toy around with the polyline output of the Valhalla routing engine in a project handling vehicle routing problems: VROOM-Project/vroom#461.

[vahancho]

Thanks for sharing. Good luck with your project.