gnome-build.html

linux下gnome编程

$ autoconf
$ ls -l
-rw-rw-r--  1 jsheets  jsheets      0 Jul  3 14:52 Makefile.in
-rwxrwxr-x  1 jsheets  jsheets  26817 Jul  3 14:52 configure*
-rw-rw-r--  1 jsheets  jsheets     36 Jul  3 14:52 configure.in
-rw-rw-r--  1 jsheets  jsheets      0 Jul  3 14:52 main.c
        </PRE
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><P
>          The autoconf command parses the configure.in macro file and
          expands it into the configure shell script file. But look at
          the size of it: 26,000 bytes- almost 800 lines for a script
          that doesn't do anything. Where is autoconf getting all
          those bytes?
        </P
><P
>          Take a look at it in your favorite editor. You'll see a very
          long list of variable declarations, most of them at first
          glance quite cryptic. You'll also see the code that
          generates the --help listing. The configure script is pretty
          well commented, so if you're curious about how it works,
          you should be able to learn a lot by studying it. Of
          particular note are the last couple hundred lines of the
          file; this code creates two files: config.cache and
          config.status. The first is a temporary file for storing the
          test results between successive calls to configure, so that
          configure doesn't have to run time-consuming tests every
          time. If configure finds the results of a test in
          config.cache, it grabs the results from there rather than
          running the test again.
        </P
><P
>          The second file, config.status, is another shell script,
          used to convert foo.in files into foo files by performing
          variable substitution (as described in Section 3.1.3). Most
          of this processing is simple text replacement, to
          customize certain files according to configure's test
          results.  For example, if configure discovers that a system
          uses the GNU gawk tool instead of the standard variant, awk,
          it can insert the string "gawk" directly into the Makefile
          file on that system.
        </P
><P
>          Most of the time you won't have to worry about these two
          files. You'll just run configure, and configure will take
          care of the rest. If you make a change to configure.in that
          involves a cached test result, you may have to delete the
          old config.cache file to force configure to run the test
          again from scratch. The only time you would want to run
          config.status by hand might be to regenerate your makefiles
          according to the current set of configure options; if you
          modified a makefile during testing and wanted to restore
          it, you could delete it and then run config.status to
          recreate it in its original form from the Makefile.in file.
        </P
><P
>          Let's try running the configure script we created
          earlier. Here's a sample session:
        </P
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><PRE
CLASS="PROGRAMLISTING"
>$ ./configure
creating cache ./config.cache
updating cache ./config.cache
creating ./config.status
creating Makefile
$ ls -lt
-rw-rw-r--  1 jsheets  jsheets      0 Jul  3 14:58 Makefile
-rw-rw-r--  1 jsheets  jsheets    127 Jul  3 14:58 config.log
-rw-rw-r--  1 jsheets  jsheets    768 Jul  3 14:58 config.cache
-rwxrwxr-x  1 jsheets  jsheets   4576 Jul  3 14:58 config.status*
-rwxrwxr-x  1 jsheets  jsheets  26817 Jul  3 14:52 configure*
-rw-rw-r--  1 jsheets  jsheets      0 Jul  3 14:52 Makefile.in
-rw-rw-r--  1 jsheets  jsheets      0 Jul  3 14:52 main.c
-rw-rw-r--  1 jsheets  jsheets     36 Jul  3 14:52 configure.in
        </PRE
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>          We have four new files. Figure 3.1 shows the process
          graphically. Aside from the config.cache and config.status
          files we saw in the configure listing, we also see the
          config.log file (empty except for the opening comments
          because we didn't run any real tests), and the Makefile file
          generated from Makefile.in. The config.log file is good for
          debugging the configuration process. As configure chugs
          along, it dumps its test results into config.log.  When
          tests fail with cryptic errors, you can often find out more
          about the failure by looking at this file.
        </P
><DIV
CLASS="FIGURE"
><A
NAME="AEN314"
></A
><P
><B
>Figure 3-1. Running the configure Script</B
></P
><DIV
CLASS="MEDIAOBJECT"
><P
><IMG
SRC="figures/3f1.png"
></IMG
></P
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><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN319"
>Makefile Variable Substitution</A
></H2
><P
>          Since our Makefile.in file in Section 3.1.2 was empty, the
          output file, Makefile, was also empty. Let's try putting
          something in Makefile.in to see what we get. We'll start
          with a simple comment:
        </P
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CLASS="PROGRAMLISTING"
>$ echo "# This is Makefile.in" &#62; Makefile.in
$ ./configure
loading cache ./config.cache
creating ./config.status
creating Makefile
$ cat Makefile
# Generated automatically from Makefile.in by configure.
# This is Makefile.in
        </PRE
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><P
>          The entire contents of Makefile.in were copied into
          Makefile, along with a reminder that the Makefile was not
          handwritten.
        </P
><P
>          Next we'll attempt some variable substitution to see how
          configure passes information to your compiler. This is where
          things start to get a little more complex. The first step is
          to add the variable substitution to configure.in.  The next
          time the autoconf script parses configure.in, the new
          variable will show up in the configure script as part of
          config.status. Since config.status creates the makefiles, it
          must also handle the variable substitutions. So let's get
          started. Change your configure.in file to look like Listing
          3.1.
        </P
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><PRE
CLASS="PROGRAMLISTING"
>Listing 3.1 configure.in with Variable Substitutions

AC_INIT(main.c)
VERSION="0.0.1"
AC_SUBST(VERSION)
AC_OUTPUT(Makefile)
        </PRE
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><P
>          VERSION will become a shell script variable in
          configure. Anything that is not a special macro will be
          copied verbatim from configure.in to configure.  But this is
          not what we want. As soon as configure is done running, the
          shell process will die and the value of VERSION will be
          lost. That's where the AC_SUBST macro comes into
          play. AC_SUBST adds VERSION to the list of variables on
          which substitutions will be performed. In fact, all
          substitutions in config.status are put there by AC_SUBST at
          some time or another.
        </P
><P
>          To make sure the wrong substitutions don't take place,
          config.status looks only for variables delimited with the
          symbol @. Thus to substitute the value of our VERSION shell
          script variable into Makefile, we must refer to it as
          "@VERSION@" in Makefile.in. Perform the following commands
          to see how it works:
        </P
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CLASS="PROGRAMLISTING"
>$ echo "# Makefile for version @VERSION@" &#62; Makefile.in
$ echo "VERSION = @VERSION@" &#62;&#62; Makefile.in
$ cat Makefile.in
# Makefile for version @VERSION@
VERSION = @VERSION@
$ autoconf
$ ./configure
loading cache ./config.cache
creating ./config.status
creating Makefile
$ cat Makefile
# Generated automatically from Makefile.in by configure.
# Makefile for version 0.0.1
VERSION = 0.0.1
        </PRE
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><P
>          Remember, if you fail to run autoconf after altering
          configure.in, none of your changes will propagate to your
          makefiles.
        </P
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