Message-Id: <m0wgWh4-000S1mC@ciati.edu.ar>
Comments: Authenticated sender is <salvador AT natacha DOT inti DOT edu DOT ar>
From: "Salvador Eduardo Tropea (SET)" <salvador AT inti DOT edu DOT ar>
Organization: INTI
To: e DOT d DOT k DOT i DOT s DOT e DOT r AT j DOT a DOT x DOT n DOT e DOT t DOT c DOT o DOT m (M. Edward Kiser), djgpp AT delorie DOT com
Date: Tue, 24 Jun 1997 17:55:16 +0000
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Subject: Re: Precompiled headers.
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> e DOT d DOT k DOT i DOT s DOT e DOT r AT j DOT a DOT x DOT n DOT e DOT t DOT c DOT o DOT m (M. Edward Kiser) wrote:
> "John M. Aldrich" <fighteer AT cs DOT com> wrote:
> >Gregary J Boyles wrote:
> >> 
> >> Does DJGPP have them?
> 
> >What are they?  And why would you want them?  Headers get inserted into
> >your code by the preprocessor and compiled along with the rest of your
> >program.  I'm afraid that I don't understand what you're asking.
> 
> To answer the second question, pre-"compiled" headers are actually
> pre-PARSED headers. To generate a pre-"compiled" header file, the
> compiler dumps its symbol table after parsing the header files; to use
> it, the compiler merely reads this symbol table back in instead of
> parsing the header files again. Obviously, this is only useful if you
> have a lot of CPP files that #include the SAME headers in the SAME
> order. But many programs do this, especially with large complicated
> header files like windows.h, the Standard Template Library, or any
> large windowing framework such as SWORD or OWL. Pre-compiled headers
> can speed things up a LOT.
I agree that's a good feature, but I don't know if gcc will be benefited from 
that, just take some code that uses includes heavilly (TVision code for 
example), run it in a Loose 95 box but windowed (not full screen), pay 
attention to the name of the window, it will change from cpp to cc1plus 
according to the program that's executing the command.com. You'll see that cpp 
is fast in comparisson with cc1plus. Now you can say: But it will speedup the 
cpp part and a 10% is usefull. For that you must take in count that precompiled 
headers must be loaded to memory and saved to disk so the impact won't be so 
huge. I guess it works very well for Borland compilers because the preprosses 
part is equally fast than cpp but the real compiler is much more faster so the 
percent is greater.
Anyways, it can speed up gcc, at least a little. 
Ah! I almost forget that: Don't forget the size!, for C medium projects a 2Mb 
file is common in BC, for huge C++ projects .... I don't think that's a good 
idea the way Borland implements that, I guess is better one file per .o and not 
one per project.

SET

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