Group header files in C and/or Objective-C

Question

I have on occasion used a header file purely to import a group of related header files that describe the interfaces on all public components of a module. This was done for convenience. Anyone using the module need only import the one header file.

Is this practice recommended, and if so does said practice have a name? I am trying to name the header files something that explicitly states that they are a group imports and am wondering if there is any convention?

Answer 1

All Cocoa frameworks do this: For example AppKit.framework contains a header name "AppKit.h" so that one can include all of AppKit using #import <AppKit/AppKit.h>. It simply contains a list of ~ 180 header import statements.

I don't have a name for this pattern but I use it in my own libraries as well (static or framework).

Answer 2

In case of Objective-C the situation is a little bit better with the #import directive, however, in C/C++ this would be a very bad thing to do, since any change to any of the interfaces described in those headers would trigger an inevitable rebuild of all .c/.cpp files including the one you use.
Should you at some point discover things like TDD or at least just unit tests, you'd have to fight with potentially very complicated dependencies introduced by such header.
I would personally recommend to avoid such solutions, unless you know what you're doing.

Answer 3

It's OK, but with one caveat: as much as possible, try not to include header files that you don't need.

If fewer headers are included, then there is less dependency on the headers, and hence between modules, and fewer files will need to be recompiled if a header changes.

A common pattern in C for embedded systems is to have one header (provided by the processor manufacturer) which includes all the separate headers defining the registers for the processor's peripherals, with that one header included in every source file. Besides that, source files only include the headers they actually need.

(In the above, "header" means a header file with .h extension, and "included" refers to the #include preprocessor directive).