precompiled headers .gch?

i dont know about this yet here is something from gtkmm july 2004

• From: "Cristian Adam"
• To: gtkmm-list gnome org
• Subject: [gtkmm] precompiled headers [revisited]
• Date: Wed, 21 Jul 2004 21:47:36 +0200 (MEST)

---

Take this small gtkmm application:

hello.cpp:
//--------------------------------------------------------
#ifdef USE_PCH
   #include "precompiled.h"
#else
   #include 
#endif

int main(int argc, char* argv[])
{
   Gtk::Main kit(argc, argv);

   Gtk::Window window;

   Gtk::Main::run(window);

   return 0;
}

precompiled.h
//--------------------------------------------------------
#ifndef PRECOMPILED_H
#define PRECOMPILED_H

#include 

#endif


The command to create the precompiled header was:
g++ -o precompiled.h.gch precompiled.h `pkg-config --cflags gtkmm-2.4`

The command to compile hello was:
time g++ -o hello hello.cpp `pkg-config --cflags --libs gtkmm-2.4` -DUSE_PCH

The results are below:

With PCH    Normal
--------------------
0m1.172s    0m6.955s
0m1.168s    0m6.930s
0m1.173s    0m7.154s
--------    --------
0m1.171s    0m7.013s

The compilation was ~6 (six) times faster with precompiled headers!!!

Precompiled headers rulle!!!

Cheers,
Cristi.

• From: Christer Palm
• To: Cristian Adam
• Cc: gtkmm-list gnome org
• Subject: Re: [gtkmm] precompiled headers [revisited]
• Date: Thu, 22 Jul 2004 01:49:39 +0200

---

Cristian Adam wrote:

The compilation was ~6 (six) times faster with precompiled headers!!!

Precompiled headers rulle!!!

OK - I'm seeing similar results now (even with more complex examples - about 4 times faster). I guess my problem was that the precompiled header should be named gtkmm.h.gch and not gtkmm.gch. However, I quickly stumbled across GCC bug 13675 (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13675), which was rather easily worked around by using 2 include files like:

A.h:
#ifndef A_INCLUDED
#define A_INCLUDED
#include "B.h"
#endif

B.h:
#include 

and then precompiling B.h, while including A.h in my source files. So it seems that it's not quite ready for prime time yet, but I still think it'd be rather interesting to have a build target for gtkmm.h.pch in the standard gtkmm makefile.

--
Christer Palm

and from
http://www.gtkmm.org/docs/gtkmm-2.4/docs/tutorial/html/sec-visual-studio-new-project.html



   The next thing to alter is the stdafx.h precompiled
   header file. At the time of this writing, many Windows programmers are
   familiar with the concept of precompiled headers. However, many Unix
   programmers are not, as precompiled header support was only recently added
   to GCC (in version 3.4) and is still not used in most open source projects.
   Unix programmers may be tempted to just disable precompiled headers
   altogether, but think carefully before doing this. Proper use of precompiled
   headers provides a much improved compile time when using gtkmm, and will
   save you many hours over the course of a project.