Where should non-interface function prototypes be placed?

Question

I've read repeatedly that header files should include all the declarations that other files will need to use the source code. Suppose then that you have a function that is not used directly by other source files (a non-interface function, in other words). Should its prototype be placed at the top of the .c file, since it will not be used by other files? Or should it be placed in the header files with all the other functions, in order to fully summarize the functions present in the .c file in one place?

Answer 1

The header contains the interface information (whatever is needed for the outside world to use the functionality in the "module" -- e.g. the .c file). So internal functions (that are not used from outside), do not go into the header

In the .c file it depends on organization

• some people like to list all internal function declaration at the top, so they are in one place.
• others rely on ordering so a function is defined by the time it is used (in another function); and only forward declare it if necessary (e.g. recursive functions that call each other)