Separating C++ Class Code into Multiple Files, what are the rules?

Question

Thinking Time - Why do you want to split your file anyway?

As the title suggests, the end problem I have is multiple definition linker errors. I have actually fixed the

Answer 1

Do standards like this exist in industry?

Yes. Then again, coding standards that are rather different from the ones you expressed can also be found in industry. You are talking about coding standards, after all, and coding standards range from good to bad to ugly.

Will the standard I came up with work in all cases?

Absolutely not. For example,

template  class Foo {
public:
   void some_method (T& arg);
...
};

Here, the definition of class template Foo doesn't know a thing about that template parameter T. What if, for some class template, the definitions of the methods vary depending on the template parameters? Your rule #2 just doesn't work here.

Another example: What if the corresponding source file is huge, a thousand lines long or longer? At times it makes sense to provide the implementation in multiple source files. Some standards go to the extreme of dictating one function per file (personal opinion: Yech!).

At the other extreme of a thousand-plus line long source file is a class that has no source files. The entire implementation is in the header. There's a lot to be said for header-only implementations. If nothing else, it simplifies, sometimes significantly, the linking problem.