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<html>
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<head>
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<title>Using Autoconf With Mktclapp</title>
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</head>
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<body bgcolor="white">
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<h1 align=center>Using Autoconf With Mktclapp</h1>
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<p>This article describes one approach for using
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<a href="http://www.gnu.ai.mit.edu/software/autoconf/autoconf.html">autoconf</a>
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to generate configure scripts for projects that use
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mktclapp.  The configure scripts that are generated using this
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approach have been tested to compile natively
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on Linux, Windows95 (Cygwin20), SunOS,
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and HPUX and to cross-compile from Linux to Windows95.  The
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configure script also supports using a build directory that
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is completely independent of the source directory.  The source
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code can even be on a read-only filesystem, such as a CD-ROM.</p>
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<p>This information is provided as a public service, with the hope
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that it might be useful to someone.  There is no warranty as to
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how well this system works.  Nor is there any promise of support.</p>
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<h2>Overview</h2>
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<img src="config.jpg" align=right>
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<p>The image to the right gives an overview of how the scheme described
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in this article works.
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The developer must come up with two input files:
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<b>configure.in</b> and <b>makemake.tcl.in</b>.  The
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first file, <b>configure.in</b> is the M4 script that autoconf
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uses to generate its <b>configure</b> shell script.  There
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is a template <b>configure.in</b> file included with this
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article that should work in most applications with
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little or no modification.  The <b>makemake.tcl.in</b>
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is a TCL script that will be used to generate a
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Makefile for the project.  The <b>configure</b> script
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will make a few modifications to this TCL script before
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it runs, in order to customize it for the target platform.
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A template <b>makemake.tcl.in</b> is also included with
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this article.</p>
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<p>After generating the <b>configure.in</b> file, the developer
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then runs GNU Autoconf version 1.13 to generate a
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<b>configure</b> shell script.  The <b>configure</b> shell
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script becomes part of the source tree.  The <b>configure</b>
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shell script is not considered a build product.  It is placed
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under configuration management just like any other source
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file.</p>
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<p>To build the project, the developer creates a new
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directory that is separate from the source tree.
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Suppose the source tree is rooted in a directory named
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<b>src</b> which is a peer of the build directory which
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is named <b>bld</b>.  To build the project, the developer
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changes to the <b>bld</b> directory and types:</p>
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<blockquote><pre>
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../src/configure
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</pre></blockquote>
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<p>This command runs the configure script that autoconf
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generated.  The configure script examines the system on
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which it is running, discovers an appropriate C compiler,
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compiler options,
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Tcl/Tk libraries, and BLT libraries, then generates
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a <b>Makefile</b> and a file named <b>makemake.tcl</b>
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based on <b>makemake.tcl.in</b>.  All of these generated
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files are in the build directory.  (Notice that the
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<b>Makefile</b> is built without a template <b>Makefile.in</b>.
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This is a bit unusual for autoconf, but it is part of
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the design.  Read on...)<p>
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<p>After the configure script is run, the developer
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types:</p>
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<blockquote><pre>
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make
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</pre></blockquote>
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<p>This command launches the make utility on the <b>Makefile</b>
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that the <b>configure</b> script generated.  This <b>Makefile</b>
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is very simple.  About all it does is run <b>makemake.tcl</b>
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to generate a new makefile called <b>all.mk</b>.  The make
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program then calls itself recursively on the newly generated
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<b>all.mk</b> in order to build the project.  Note that the
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project is build in the local directory, not the source directory.
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Note also that
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any old version of the make utility will do.  GNU make is
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not required.</p>
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<br clear=both>
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<h2>Advantages To This Approach</h2>
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<p>There are, of course, many ways to make use of autoconf.
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And most other ways are more conventional that the scheme
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described above.  But this approach does have certain
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advantages.</p>
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<ul>
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<li>
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   <p><b>The same source directory can be used to build for multiple
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   targets.</b></p>
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   <p>By putting the source tree on an NFS- or SMB-mounted filesystem,
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   lots of different computers can read the sources at the same time.
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   And they can all compile off of the same source tree, putting there
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   build products in separate directories.  The separate builds can
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   even take place at the same time.</p></li>
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<li>
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   <p><b>The source tree can be on a read-only filesystem.</b></p>
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   <p>This allows you to compile directly from a source tree
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   located on a CD-ROM, for example.  There is no need to copy
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   the source tree onto read-write media prior to the build.</p></li>
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<li>
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   <p><b>The use of "tclsh" in the build process gives much more
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   control to the developer.</b></p>
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   <p>A makefile is not a program.  There are a lot of interesting
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   things that a makefile will not do.  For example, standard makefiles
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   have no provisions for conditional compilation.  (GNU make has
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   this capability, but GNU make is not standard and is not
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   installed on every system.)  Running tclsh to generate the makefile
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   allows the developer to radically change the build process depending
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   on the characteristics of the target machine.</p></li>
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</ul>
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</p>
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<h2>How To Adapt This Approach To Your Own Project</h2>
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<p>If you want to try using the build scheme described here,
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first get a copy of the <b>configure.in</b> template.  You
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can find the template at:</p>
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<blockquote>
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<a href="http://www.hwaci.com/sw/mktclapp/configure.in">
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http://www.hwaci.com/sw/mktclapp/configure.in
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</a>
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</blockquote>
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<p>You will need to modify this file to suit your application.
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But the modifications are normally modest.  First change the
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argument of the AC_INIT() macro to be the name of a file
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in your project's source tree.  If your project does not
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use the BLT extension, then disable the tests for
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BLT by commenting them out.
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If your project uses some extensions other
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than BLT, you may have to add new test to the <b>configure.in</b>.
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Use the existing code as your guide.</p>
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<p>The <b>configure.in</b> contains comments to help you understand
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how it works.  You may also want to refer to the Autoconf
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manual for information on the Autoconf macros.</p>
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<p>The next step is to generate a suitable <b>makemake.tcl.in</b>.
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You can begin with the template at:</p>
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<blockquote>
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<a href="http://www.hwaci.com/sw/mktclapp/makemake.tcl.in">
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http://www.hwaci.com/sw/mktclapp/makemake.tcl.in
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</a>
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</blockquote>
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<p>The template is really a working <b>makemake.tcl.in</b> file for
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a specific project.  The project is not Open-Source and so the
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source code is not available.  But that is not important.  The
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comments in the template file should give you plenty of guidance
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on how to adapt the template to your particular project.  Remember,
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you are working with plain ordinary TCL code.  The output of
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the script will become a makefile.  Be creative.</p>
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<p>The final step is to run autoconf version 1.13 or later
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to generate the <b>configure</b> script.  You can obtain a
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copy of autoconf from lots of places on the net.  Use a
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search engine to find one near you if you don't already have
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autoconf installed on your machine.</p>
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<h2>Parting Words</h2>
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<p>For additional information, read the template files.</p>
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<p>It is important to emphasize that there are many different
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ways of building a project, and many different ways of using
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autoconf.  You are welcomed to use the approach outlined here
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if it suits your needs.  Hopefully you will find this information
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helpful.  But the techniques described here will not work in
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every circumstance.  You may have to change things.  You may
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have to use a completely different build scheme.</p>
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<p>If you fix bugs or make extensions to the template files described above,
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then patches sent to the author at
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<a href="mailto:drh@hwaci.com">drh@hwaci.com</a> will be
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welcomed.  Your patches will be gratefully acknowledged and
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added to the distribution.   Reports of bugs without fixes,
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or requests for new features, may or may not be acknowledged.
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</body>
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