Re: Multiple definition of VERSION, PACKAGE and so on

[Tim Van Holder]

Patrick Guio wrote:

> On Tue, 23 Mar 2004, Guido Draheim wrote:
>
> > As said before - it is TOTAL ERROR to include config.h (here: pack1-config.h)
> > into header files made publically available to outside projects (here: pack2).
>
> I would definitely like to hear how do you handle the following solution
> if you mean this is TOTAL ERROR to include config.h into header files
> that are made publically available to outside projects.
> As far as now I have a pack1-defs.h header file containing definitions like:
>
> #if defined(HAVE_CONFIG_H)
> #include <pack1-config.h>
> #endif
>
> #if defined(FLOAT_FIELD)
> typedef float pack1Real;
> #elif defined(DOUBLE_FIELD)
> typedef double pack1Real;
> #else
> #error macro FLOAT_FIELD or DOUBLE_FIELD must be defined
> #endif
>
> typedef blitz::Array<pack1Real,1> Array1dr;
> typedef blitz::Array<pack1Real,2> Array2dr;
> typedef blitz::Array<pack3Real,3> Array3dr;
>
> typedef blitz::Array<pack1Real,DIM> Field;

For simple cases like the above, one way would be to do something
like this:

[configure.ac]
...
if ...; then
  my_real_type_var=double
else
  my_real_type_var=float
fi
...
AC_SUBST([BLITZ_REAL_TYPE], $my_real_type_var)
...
AC_CONFIG_FILES([pack1-defs.h:pack1-defs-h.in])
...

[pack1-defs-h.in]
...
typedef @BLITZ_REAL_TYPE@ pack1Real;
...


In your code, the #error suggests that it would be OK for the client
code to provide FLOAT_FIELD or DOUBLE_FIELD, when in fact that decision
has already been made during pack1's configuration.  What's more, you
leave the inclusion of pack1's config.h up to the user (who has to
define HAVE_CONFIG_H for you).
Typically, every installed file that in some way depends on
configuration-time variables will be an autoconf output file.
AX_PREFIX_CONFIG_HEADER is a way around this for cases where there are
so many relevant #defines that the approach shown becomes impractical.