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From: jeffa@hpmwtd.HP.COM (Jeff Aguilera)
Newsgroups: comp.lang.c++
Subject: Re: A solution to the multiple inclusion problem
Message-ID: <1520005@hpmwjaa.HP.COM>
Date: 27 Oct 89 18:11:58 GMT
References: <14240@well.UUCP>
Organization: HP Microwave Tech. - Santa Rosa, Ca.
Lines: 88

Here's my approach for preventing superfluous includes, without relying on the
`implementation-defined' #pragma directive, modifications to #include semantics,
or an impressively intelligent compiler.  

A module is divided into three source files:

    .h  [header]    interface definition; inlines prohibited
    .m  [macro]     inlines; one-liners and common idioms only
    .c  [c]         C++ source

Each .[hmc] file normally includes just one other file, a corresponding 
preprocessor file .[hmc]pp:

    //foo.h -- a foo gadget
    #include "foo.hpp"
    <interface>

    //foo.m -- a foo gadget
    #include "foo.mpp"
    <inlines>

    //foo.c: foo.h -- a foo gadget
    #include "foo.cpp"
    <C++ implementation>

These preprocessor files are generated automatically from the source by
inspecting the first line, and extracting comments that look like this:

    //use: "foo.h bar.h"
    //use: <string.h iostream.h X11/Xlib.h>

The `extract .?pp' program (xpp) generates files that look like this:

    //foo.hpp
    #ifndef foo_h
    #define foo_h "Fri Oct 27 10:25:37 PDT 1989 foo.h"
    #endif

    //foo.mpp
    #ifndef _memory_h
    #include <memory.h>
    #ifndef _memory_h
    #define _memory_h
    #endif
    #endif

    //foo.cpp
    #define self (*this)
    #include "foo.h"
    #include "foo.m"
    #ifndef _string_h
    #include <string.h>
    #ifndef _string_h
    #define _string_h
    #endif
    #endif
    #ifndef _iostream_h
    #include <iostream.h>
    #ifndef _iostream_h
    #define _iostream_h
    #endif
    #endif
    #ifndef _X11_Xlib_h
    #include <X11/Xlib.h>
    #ifndef _X11_Xlib_h
    #define _X11_Xlib_h
    #endif
    #endif
    #ifndef bar_h
    #include "bar.h"
    #include "bar.m"
    #endif

Xpp also extracts comments of the form //bug: and colates the results in a
correspondind `bug-bucket' file, .?bb:

    //foo.cbb
    Known bugs as of Fri Oct 27 10:31:07 PDT 1989
      45:   X& X::operator=(const X&) not implemented
      87:   should raise software assertion rather than aborting
     134:   EOF[3CB7] 2599 characters 

Xpp also forces a file naming policy, so that porting applications between UNIX
and DOS is only a minor nuisance.  (Case sensitivity, length, character set,
extension.)  Still no topological sort on include dependencies....

--------
    jeff "reinventing rounder wheels" aguilera