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24.4 Example: The Full Pull

Suppose instead that I wanted to fully autoconfiscate zip. Let’s ignore for now that zip can build on systems to which the GNU Autotools have not been ported, like TOPS-20—perhaps a big problem back in the real world.

The first step should always be to run autoscan. autoscan is a program which examines your source code and then generates a file called ‘configure.scan’ which can be used as a rough draft of a ‘configure.in’. autoscan isn’t perfect, and in fact in some situations can generate a ‘configure.scan’ which autoconf won’t directly accept, so you should examine this file by hand before renaming it to ‘configure.in’.

autoscan doesn’t take into account macro names used by your program. For instance, if autoscan decides to generate a check for ‘<fcntl.h>’, it will just generate ordinary autoconf code which in turn might define ‘HAVE_FCNTL_H’ at configure time. This just means that autoscan isn’t a panacea – you will probably have to modify your source to take advantage of the code that autoscan generates.

Here is the ‘configure.scan’ I get when I run autoscan on zip:

dnl Process this file with autoconf to produce a configure script.

dnl Checks for programs.

dnl Checks for libraries.
dnl Replace `main' with a function in -lx:
AC_CHECK_LIB(x, main)

dnl Checks for header files.
AC_CHECK_HEADERS(fcntl.h malloc.h sgtty.h strings.h sys/ioctl.h \
termio.h unistd.h)

dnl Checks for typedefs, structures, and compiler characteristics.

dnl Checks for library functions.
AC_CHECK_FUNCS(getcwd mktime regcomp rmdir strstr)

AC_OUTPUT(acorn/makefile unix/Makefile Makefile atari/Makefile)

As you can see, this isn’t suitable for immediate use as ‘configure.in’. For instance, it generates several ‘Makefile’s which we know we won’t need. At this point there are two things to do in order to fix this file.

First, we must fix outright flaws in ‘configure.scan’, add checks for libraries, and the like. For instance, we might also add code to see if we are building on Windows and set a variable appropriately:

case "$target" in
  *-cygwin* | *-mingw*)
    # Assume Unix.

Second, we must make sure that the zip sources use the results we compute. So, for instance, we would check the zip source to see if we should use ‘HAVE_MMAP’, which is the result of calling AC_FUNC_MMAP.

At this point you might also consider using a configuration header such as is generated by AC_CONFIG_HEADER. Typically this involves editing all your source files to include the header, but in the long run this is probably a cleaner way to go than using many -D options on the command line. If you are making major source changes in order to fully adapt your code to autoconf’s output, adding a ‘#include’ to each file will not be difficult.

This step can be quite difficult if done thoroughly, as it can involve radical changes to the source. After this you will have a minimal but functional ‘configure.in’ and a knowledge of what portability information your program has already incorporated.

Next, you want to write your ‘Makefile.am’s. This might involve restructuring your package so that it can more easily conform to what Automake expects. This work might also involve source code changes if the program makes assumptions about the layout of the install tree – these assumptions might very well break if you follow the GNU rules about the install layout.

At the same time as you are writing your ‘Makefile.am’s, you might consider libtoolizing your package. This makes sense if you want to export shared libraries, or if you have libraries which several executables in your package use.

In our example, since there is no library involved, we won’t use Libtool. The ‘Makefile.am’ used in the minimal example is nearly sufficient for our use, but not quite. Here’s how we change it to add dependency tracking and dist support:

## Process this file with automake to create Makefile.in.

bin_PROGRAMS = zip

bin_SCRIPTS = unix/zipgrep
os_sources = unix/unix.c
os_sources = win32/win32.c win32zip.c
zip_SOURCES = zip.c zipfile.c zipup.c fileio.c util.c globals.c \
              crypt.c ttyio.c crc32.c crctab.c deflate.c trees.c \
              bits.c $(os_sources)

## It was easier to just list all the source files than to pick out the
## non-source files.
EXTRA_DIST = algorith.doc README TODO Where crc_i386.S bits.c crc32.c \
acorn/RunMe1st acorn/ReadMe acorn/acornzip.c acorn/makefile \
acorn/match.s acorn/osdep.h acorn/riscos.c acorn/riscos.h \
acorn/sendbits.s acorn/swiven.h acorn/swiven.s acorn/zipup.h crctab.c \
crypt.c crypt.h deflate.c ebcdic.h fileio.c globals.c history \
wizdll/wizdll.def wizdll/wizmain.c wizdll/wizzip.h wizdll/zipdll16.mak \

The extremely long ‘EXTRA_DIST’ macro above has be truncated for brevity, denoted by the ‘...’ line.

Note that we no longer define INCLUDES – it is now automatically defined by configure. Note also that, due to a small technicality, this ‘Makefile.am’ won’t really work with Automake 1.4. Instead, we must modify things so that we don’t try to compile ‘unix/unix.c’ or other files from subdirectories.

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This document was generated by Ben Elliston on May 30, 2015 using texi2html 1.82.