问题
What is the normal practice when it comes to non-member function in C++? Do we put them in main.cpp or header file or class implementation file, or do we make a separate .cpp file for it? If the normal practice is to make a separate file, then where do we put the non-member function header(prototype)? Does it only go in main.cpp or in both of them?
回答1:
I would say you should not treat non-member functions differently to classes and member functions and other symbols.
You should create a distinct header file .h and a corresponding source file .cpp for each logical component (module) of your application.
All public symbols should be declared/defined in the header file (whether they be non-member functions or otherwise) and all non-public symbols and all required definitions should go in the source file.
In short, group according to logical program components, rather than by the type of symbol/function.
回答2:
Your class should have its own .cpp file. Non-member functions should go in other files (all together or grouped according to similarity). That's the convention here in North America, but conventions differ. Prototype just needs go into header file so you can include it wherever you use it.
回答3:
General idea in pseudo code:
if (it will be used in other cpp files)
put the declaration in a header file.
implement it in a header or a cpp file.
else
if (only need it in some functions in a header file)
if (it's a function more than N line ) // please define this N in your mind
declare it in the same header and implement it in a cpp file
else
put it in the same header file
else // used in cpp only
put it in the cpp file
As long as it compiles, you should consider readability (easy for anyone to read) and accessibility (easy for anyone to find and debug).
来源：https://stackoverflow.com/questions/43748990/in-which-file-do-we-put-non-member-function-in-c