[vox-tech] Asking C compiler to test for #include file

[Ken Bloom]

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On 2003.07.20 08:23, Bill Kendrick wrote:
>=20
> Right now I have a program that will die if certain headers can't be
> found.
>=20
> The issue of getting these headers has practically become an FAQ for
> the libraries installed.
> ("You forgot to download the *-dev packages of the library, which
> contains the headers!")
>=20
>=20
> I'd like, if possible, GCC to barf with my OWN error, stating
> something along these lines,
> rather than just:
>=20
>   src/myprog.c:15: foo.h: No such file or directory
>=20
>=20
> I realize I can spit out an error message using the C "#error"
> directive, but is there a simple
> (and portable) way of TESTING?
>=20
> e.g.:
>=20
>   #SOME_IF-LIKE_DIRECTIVE_I_DON'T_KNOW_ABOUT
>=20
>     #include "somelib.h"
>=20
>   #else
>=20
>     #error "Ya big dummy!  You need to install the 'somelib-dev'
> package!"
>=20
>   #endif
>=20
> Is there such a thing?  I'm actually realtively unfamiliar with all of
> the C directives out there.
> I've stuck to the typical "#define", "#ifdef", "#include" trio. ;^)

Doing something with #if (a la #if defined(...)) seems tempting, but=20
there's no predefined macro to test for the existance of a file, and I=20
know of no way to create one so that's out of the question. (See=20
"Conditional Syntax" in the cpp TeXinfo manual for more information)


I don't think the header guards (the #ifndef/#define/#endif that is=20
supposed to surround every header file) are necessarily portable, but=20
you could try somehting like this:

#include "somelib.h"
#ifndef __SOMELIB_Hs_HEADER_GUARD__
   #error "Ya big dummy!..."
#endif

If "somelib.h" defines *documented* macros when it is defined, then=20
this becomes portable when you test for one of the documented macros=20
instead. This doesn't prevent #include from writing an error of its=20
own, but at least the user sees your error too.

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