Precompiled headers issue: -c and -fpch-preprocess should be used together?

Precompiled headers issue: -c and -fpch-preprocess should be used together?

[Pavel Shevaev]

Folks, I'm using gcc-4.4.1(4.4.1-4ubuntu9 to be precise) on Ubuntu and
after trying to make PCH work properly for some time I found that
precompiled headers are not used if -c option used. Experimenting with
different options I discovered that it's the -fpch-preprocess option
which enables PCH in this case.

Is it an expected behavior? If yes, maybe it should be documented here
http://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html in order to
save some time for others :)

-- 
Best regards, Pavel

Re: Precompiled headers issue: -c and -fpch-preprocess should be used together?

[Ian Lance Taylor]

Pavel Shevaev <pacha.shevaev@gmail.com> writes:

> Folks, I'm using gcc-4.4.1(4.4.1-4ubuntu9 to be precise) on Ubuntu and
> after trying to make PCH work properly for some time I found that
> precompiled headers are not used if -c option used. Experimenting with
> different options I discovered that it's the -fpch-preprocess option
> which enables PCH in this case.
>
> Is it an expected behavior? If yes, maybe it should be documented here
> http://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html in order to
> save some time for others :)

It is very likely that you are using ccache or distcc.  Those tools
first preprocess the C source code and then compile it.  It's true
that if you are preprocessing, you need to use the -fpch-preprocess
option.  However, -fpch-preprocess is not required if you do not
preprocess, and omitting it should work fine when using gcc proper
rathre than ccache or distcc.

Ian

Re: Precompiled headers issue: -c and -fpch-preprocess should be used together?

[Pavel Shevaev]

> It is very likely that you are using ccache or distcc.

You are absolutely correct, I'm using both ccache and distcc.

> Those tools
> first preprocess the C source code and then compile it.  It's true
> that if you are preprocessing, you need to use the -fpch-preprocess
> option.  However, -fpch-preprocess is not required if you do not
> preprocess, and omitting it should work fine when using gcc proper
> rathre than ccache or distcc.

Thanks for the explanation! I just wonder why not putting this info on
the pch help page somewhere?

-- 
Best regards, Pavel

Re: Precompiled headers issue: -c and -fpch-preprocess should be used together?

[Ian Lance Taylor]

Pavel Shevaev <pacha.shevaev@gmail.com> writes:

>> Those tools
>> first preprocess the C source code and then compile it.  It's true
>> that if you are preprocessing, you need to use the -fpch-preprocess
>> option.  However, -fpch-preprocess is not required if you do not
>> preprocess, and omitting it should work fine when using gcc proper
>> rathre than ccache or distcc.
>
> Thanks for the explanation! I just wonder why not putting this info on
> the pch help page somewhere?

It's kind of special purpose and I think it would fit better on
http://gcc.gnu.org/wiki/FAQ .  Want to add an entry?

Ian

Re: Precompiled headers issue: -c and -fpch-preprocess should be used together?

[Pavel Shevaev]

> It's kind of special purpose and I think it would fit better on
> http://gcc.gnu.org/wiki/FAQ .  Want to add an entry?

I'll give it a try :)

-- 
Best regards, Pavel