c++ template and header files
c++, file, header, templates
Solution
Headers.
It's because templates are instantiated at compile-time, not link-time, and different translation units (roughly equivalent to your `.cpp` files) only "know about" each other at link-time. Headers tend to be widely "known about" at compile-time because you `#include` them in any translation unit that needs them.
Read https://isocpp.org/wiki/faq/templates for more.
Problem
So, I heard that C++ templates shouldn't be separated into a header (.h) and source (.cpp) files. For instance, a template like this: ``` template <class T> class J { T something; }; ``` Is this true? Why is it so? If because of that I'm gonna have to put both declaration and implementation in the same file, should I put it in a .h file or a .cpp file?