What should go into an .h file?

Question

When dividing your code up into multiple files just what exactly should go into an .h file and what should go into a .cpp file?

Answer 1

In general, you put declarations in the header file and definitions in the implementation (.cpp) file. The exception to this is templates, where the definition must also go in the header.

This question and ones similar to it has been asked frequently on SO - see Why have header files and .cpp files in C++? and C++ Header Files, Code Separation for example.