Re: [jamboost] PCH support

From: Toon Knapen (toon.knapen_at_[hidden])
Date: 2004-09-03 06:36:25

Vladimir Prus wrote:

> I'd think that header should only include standard headers, not the 
> application's headers.

I understand that PCH support is not easy but if it is available, it 
should also be able to use precompiled headers for non-system headers 
(i.e. application headers) IMO.

> 
> Another danger is that if all translation units include the central header, 
> which grabs <vector>, <map>, <algorithm> and the like, then the programmers 
> might forget to add those include to translation units themself, so with 
> "USE_PCH" undefined there will be compile errors. Seems not good for 
> cross-platform programming.
> 

I also wondered about this so I'm keen to know the answer too.

> 2. gcc
> 
> Gcc, too, has two models. You start by compiling a header file. In the first 
> model, the compiled header is placed somewhere in include path, and if you 
> try to include that header, the precompiled version is used. That is, all 
> translation units still have to include a central header. In the second 
> model, you add "-include" option to the compiler, which cause it to load the 
> header before compiling the translation unit. This is handy, because it avoid 
> modifying all translation units. The problem is still that translation unit 
> which uses std::vector without include <vector> will compile fine with PCH, 
> but won't compile elsewhere.

Anyway, to benefit from PCH, it is best to make a giant header which 
includes all headers IIUC (as read in C++ templates of Vandevoorde and 
Josuttis). Because a including the same headers but in a different order 
results in a different compiler-state.