Re: [jamboost] Finding out where output files are and changing it + precompiled headers

From: Andrey Melnikov (melnikov_at_[hidden])
Date: 2005-07-06 10:49:24

Vladimir Prus wrote:
> Hi Andrey,
> Hi Jim,
> 
> 
>>>2. In my compiler flags <cflag> I'd like to reference the output
>>>directory (the one we changed in 1). This is for this specific instance
>>>for precompiled headers, so the actual flag I want to pass is something
>>>like this (but of course I don't know the proper variablenames):
>>>
>>><cflag>-Fp$(intermediate_path)/$(project_name).pch
>>
>>It isn't a good idea to specify cflags manually in jamfile. It's better
>>to patch msvc.jam toolset definition file and create features like
>>
>><pch>off|use|create|hdrstop
>><pch-header>StdAfx.h
>><pch-db>StdAfx.pch
>>
>>Also you need to track dependencies correctly: all files with <pch>use
>>should depend on StdAfx.pch, and stdafx.cpp should create StdAfx.pch
>>output.
>>
>>Can someone more fluent in bbv2 tell me is this a lot of work?
> 
> 
> This PCH thing becomes a common request. Recall that msvc has both "automatic" 
> pch mode, that requires, IIRC, a single switch, and "manual" mode, that 
> requires creating PCH once, and then using it from other targets. 

I named "automatic" mode "hdrstop", because it requires #pragma hdrstop. 
Borland compilers support #pragma hdrstop too, and Jamfile with 
<pch>hdrstop would be portable at least between intel-win, msvc and borland.

Another thing to consider is that MSVC2005 deprecates this "hdrstop" method.

> I recall 
> I've suggested the following syntax for the manual mode:
> 
> pch stl : stl.h :
> exe my : my.cpp : <pch>stl ;
> 

This would be perfect. But what about stl.cpp? It's a file with single 
#include "stl.h" line. It's required to create stl.obj. And stl.obj then 
should be linked into my.exe. Do you think all these things can be 
supported with this simple syntax?

> I think this should not be too hard to add. 
> 
> 
>>Also I wonder how other compilers besides msvc implement precompiler
>>headers? 
> 
> borland, como, gcc

But HOW do they implement this feature? What users have to do besides 
adding command line switches to enable them? I know 2 methods: including 
special header and #pragma hdrstop. I wonder how portable precompiled 
headers can be.

>>It looks like bcb can use #pragma hdrstop too. 
> 
> And, BTW, I forgot that #pragma hdrstop does ;-) Gcc does not have it, IIRC.

When automatic precompiled headers are enabled, compiler adds headers to 
precompiled header database until it reaches #pragma hdrstop:

#include <iostream>
#pragma hdrstop
#include "hello.h"

int main()
{
std::cout << "Hello!\n";
return 1;
}

In this case <iostream> will be precompiled, and hello.h won't.

Andrey