C编程：预处理器，包含宏中的文件

Question

If I could find a way to do something similar to this, I could cut out hundreds of lines of code in my application, and dramatically increase maintainability. Anyone have any ideas?

#include <stdio.h>

int main( )
{
  #define include_all_files(root)   \
            #include #root "1.h"    \
            #include #root "2.h"    \
            #include #root "3.h"    \
            #include #root "4.h"

  include_all_files( first_library )
  include_all_files( second_library )
  include_all_files( third_library )

  return 0;
}

EDIT :

I appreciate the responses, my example seems to be causing a misdirection in effort, so here is the problem I am actually trying to solve:

I am implementing a finite state machine. Through naming conventions, I have gotten it to be as simple to add a state as:

  STATE(initial_screen)
    #include "initial_screen.state"
  END_STATE

  STATE(login)
    #include "login.state"
  END_STATE

However, if I could answer the original question, I could refactor this down to something as simple as:

  ADD_STATE(initial_screen)
  ADD_STATE(login)

This is because the file name and the state name, and all the underlying wiring and everything else all follow similar conventions. However, I cannot figure out how to implement the include file based on the token received in a macro.

Answer 1

Why not just create a header file that itself #include s all of the other header files for the library? Then for each library you'd just include that library's one meta-header.

Answer 2

Unfortunately, this is beyond the capabilities of the C preprocessor.

Have you considered using something like m4 instead?

Answer 3

To solve your clarified problem, you could just refactor initial_screen.state and login.state so that they start with STATE() and end with END_STATE . Then you can just do:

#include "initial_screen.state"
#include "login.state"

...which is equivalent to what you're after - it's just an #include instead of an ADD_STATE .

Answer 4

In file includes.h

#include "1.h"
#include "2.h"
#include "3.h"

In all other files

#include "includes.h"

Answer 5

The #include pre-process directive being itself handled at in the same step as the macro evaluation, this would likely not work. I don't believe the pre-processing can be recursive. (or iterative, for that matter).

Instead, the typical way this is done is to create a small include file which includes all the desired #includes. See Cory Petosky's reponse for an illustration.

A word of caution :
While this may cut hundreds of line of code, you should consider that these are "easy" lines of code . One typically skims over them, unlike lines of codes associated with the true logic of the program.

Furthermore, explicitly listing the individual includes necessary for a given file provide a bit of self documentation, and make it easier for refactoring the code when needed.

Edit : This just in ;-)
Someone just asked this SO question Good idea to put all project headers into one file? , and the responses seem to generally agree with my take that there's typically little gain to be had from grouping headers.