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Re: Include directories

Quoting Viktor Rosenfeld (rosenfel@informatik.hu-berlin.de):
> David Wright wrote:
> > Are you saying that the software you downloaded has .c files and some .h
> > files specially for it? 
> Exactly! 
> > What I do in that case is to have all the .c
> > and .h files in the current directory (whereever), and use
> > something like (taken from a bash function)
> > /usr/bin/gcc -DMODULE -D__KERNEL__ -I. -I/usr/local/src/linux/include \
> > -O2 -m486 -g -Wall -c $@ -o ${SOURCE}.o ${SOURCE}.c
> That actually worked out perfectly.  I modified the Makefile so it would
> pass -I/usr/src/linux/include to gcc and it used the header files there
> instead of the ones in /usr/include.  
> I'm just wondering, how gcc knows which ones it should use.  Does it
> even look in /usr/include anymore?

I believe so, but my -I options tell it to search . and the
kernel include files first. If I were to compile an ordinary
C program (I never do), I would leave them out, so getting
/usr/include headers included instead.

> What if I pass multiple -Is to gcc
> (as you do in your example) and there are different versions of the same
> header file?

That's all handled by the incantations that wrap virtually every
header file, eg:

 * Dynamic loading of modules into the kernel.
 * Rewritten by Richard Henderson <rth@tamu.edu> Dec 1996


[snip the actual headers]

#endif /* _LINUX_MODULE_H */

Without this, almost any compilation would grind to a halt with endless
circular inclusions.


Email:  d.wright@open.ac.uk   Tel: +44 1908 653 739  Fax: +44 1908 655 151
Snail:  David Wright, Earth Science Dept., Milton Keynes, England, MK7 6AA
Disclaimer:   These addresses are only for reaching me, and do not signify
official stationery. Views expressed here are either my own or plagiarised.

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