Templates and headers question

Question

The compiler says it can\'t find the reference for the function when I do this:

// link.h
template 
    T *Link(T *&, T *(*)())

// link.c         


        

Answer 1

Programming non-template code or non-inlined functions in headers is a Bad Thing™. The reason you have cpp files is to prevent redefinition of the same function code more than once, amongst other things.

The difference with templates is that the compiler practically doesn't touch them until your code instantiates a specialisation of that template which is why they need to have their source inside the header.

When the compiler finds an instantiation of a template specialisation (say List), it goes back to the included template code and compiles it with that specialisation, which is why you don't have issues with redefinition of function code.

What you don't seem to understand is that this doesn't apply to non-templated code. All non-template code is compiled as normal and thus CPP files are needed to only define the code once then link it all together.

If you define functions inside a header, your linker will not link the compiled translation units because they have defined the same function more than once.