Very Computer

Hi,

I'm currently developing a C program and doing my best to bring the
power of GNU automake to bear on the build process. I'm now at the
stage where I can use automake fairly effectively, and consulting the
manual usually clears up any confusion I may have.

However, with this particular project, I've run into a problem that I
can't quite work out how to solve in an elegant fashion.

The problem is with a couple of source files that need to be compiled
only under certain circumstances.

I currently have a Makefile.am consisting of the following:

bin_PROGRAMS = qrcs
qrcs_SOURCES = qrcs.c qrcs.h
EXTRA_qrcs_SOURCES = ext2fs.c ext2fs.h
man_MANS = qrcs.1
EXTRA_DIST = $(man_MANS) qrcs.spec qrcs.lsm

The automake manual recommends assigning source files that are only
conditionally part of the build process to EXTRA_qrcs_SOURCES instead
of qrcs_SOURCES, so that is what I have done.

The problem comes in not knowing how to inform the build process when
it should build the EXTRA_qrcs_SOURCES files.

My configure.in checks for the existence of linux/ext2_fs.h and, if it
is found, defines HAVE_LINUX_EXT2_FS_H. That's the easy part.

When this symbol is defined, I want to compile the ext2fs.o object and
link it to the main one, qrcs.o, to form the qrcs binary.

I have solved the problem temporarily by removing the
EXTRA_qrcs_SOURCES line and adding ext2fs.c and ext2fs.h to
qrcs_SOURCES.

Of course, to make this work on non-Linux systems, I've had to edit
ext2fs.c and employ the kludge of enclosing the whole file in an
#ifdef HAVE_LINUX_EXT2_FS_H clause, which then produces a compile time
warning about ANSI C forbidding empty source files, which in turn
requires its own kludge to circumvent.

What I thus need is a way of informing the build process to build and
link EXTRA_qrcs_SOURCES only when the header file in question has been
found, but I can't work out what to put in Makefile.am to achieve
this.

The automake manual doesn't seem to provide the solution either, even
though the subject of conditional compilation *is* touched upon. Maybe
I'm barking up the wrong tree altogether.

Anyway, any help you can offer would be much appreciated.

Ian
--
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Quote:>The problem is with a couple of source files that need to be compiled
>only under certain circumstances.

>I currently have a Makefile.am consisting of the following:

>bin_PROGRAMS = qrcs
>qrcs_SOURCES = qrcs.c qrcs.h
>EXTRA_qrcs_SOURCES = ext2fs.c ext2fs.h
>man_MANS = qrcs.1
>EXTRA_DIST = $(man_MANS) qrcs.spec qrcs.lsm

>The automake manual recommends assigning source files that are only
>conditionally part of the build process to EXTRA_qrcs_SOURCES instead
>of qrcs_SOURCES, so that is what I have done.

>The problem comes in not knowing how to inform the build process when
>it should build the EXTRA_qrcs_SOURCES files.

>My configure.in checks for the existence of linux/ext2_fs.h and, if it
>is found, defines HAVE_LINUX_EXT2_FS_H. That's the easy part.

The configure.in should also conditionally set a configuration
variable, say EXT2_FS, to ext2fs.o and have your Makefile.am say:

                --Ken Pizzini

On 4 Jan 2000 17:45:00 GMT, Ken Pizzini

So when would you use the EXTRA_qrcs_SOURCES macro then?

The automake manual recommends the usage of EXTRA_$(package)_SOURCES
for files that are to be built conditionally. Is it just a question of
using this in the same way you describe using EXT2_FS?

Obviously, what you describe would work, but is that the way automake
intends you to use the EXTRA_$(package)_SOURCES construct, or is there
a better way?

Ian
--
Ian Macdonald              | A chap down in Oklahoma Had a* that    
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When you include any files which are not always built.  To quote
from the relevant section of the automake manual (which is
perhaps less than clear on the subject):
:    Automake must know all the source files that could possibly go into a
: program, even if not all the files are built in every circumstance.
: Any files which are only conditionally built should be listed in the
: appropriate `EXTRA_' variable.  For instance, if `hello-linux.c' were
: conditionally included in `hello', the `Makefile.am' would contain:
:
:      EXTRA_hello_SOURCES = hello-linux.c
:
:    Similarly, sometimes it is useful to determine the programs that are
: to be built at configure time.  For instance, GNU `cpio' only builds
: `mt' and `rmt' under special circumstances.
:
:    In this case, you must notify Automake of all the programs that can
: possibly be built, but at the same time cause the generated
: `Makefile.in' to use the programs specified by `configure'.  This is
: done by having `configure' substitute values into each `_PROGRAMS'
: definition, while listing all optionally built programs in
: `EXTRA_PROGRAMS'.

Now that last paragraph talks about "_PROGRAMS", but it
also applies to "_SOURCES": you tell automake itself about the
optionally-compiled sources with the EXTRA_qrcs_SOURCES macro,
and you tell the configure script that you want the EXT2_FS
configuration variable interpolated into the expansion of the

on the qrcs_SOURCES line.

                --Ken Pizzini