autobook_92.html

Autoconf使用手册

<TT>`error.c'</TT>.  The problem with this approach is that different
vendors will provide slightly different declarations (with or without
<CODE>const</CODE> for instance), so compilation will fail on those
architectures which <EM>do</EM> provide a declaration in the system
headers that is different from the declaration you have guessed.
</P><P>

For the benefit of architectures which do not have an implementation of
the <CODE>basename()</CODE> function, a fallback implementation is provided in
the <TT>`replace'</TT> subdirectory.  The file <TT>`basename.c'</TT> follows:
</P><P>

<TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>
</pre></td></tr></table></P><P>

For brevity, the implementation does not use any <CODE>const</CODE>
declarations which would be good style for a real project, but would
need to be checked at configure time in case the end user needs to
compile the package with a K&#38;R compiler.
</P><P>

The use of <CODE>strrchr()</CODE> is noteworthy.  Sometimes it is declared in
<TT>`string.h'</TT>, otherwise it might be declared in <TT>`strings.h'</TT>.
<FONT SIZE="-1">BSD</FONT> based Unices, on the other hand, do not have this function at
all, but provide an equivalent function, <CODE>rindex()</CODE>.  The
preprocessor code at the start of the file is designed to cope with all
of these eventualities.  The last block of preprocessor code assumes
that if <CODE>strrchr</CODE> is already defined that it holds a working macro,
and does not redefine it.
</P><P>

<TT>`Makefile.am'</TT> contains:
</P><P>

<TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>
</pre></td></tr></table></P><P>

Once again, the <SAMP>`noinst_LTLIBRARIES'</SAMP> macro names the convenience
library,<BR> <TT>`libreplace.la'</TT>.  By default there are no sources, since
we expect to have a system definition of <CODE>basename()</CODE>.  Additional
Libtool objects which should be added to the library based on tests at
configure time are handled by the <SAMP>`LIBADD'</SAMP> macro.  <SAMP>`LTLIBOBJS'</SAMP>
will contain <TT>`basename.lo'</TT> if the system does not provide
<CODE>basename</CODE>, and will be empty otherwise.  Illustrating another
feature of convenience libraries: on many architectures,
<TT>`libreplace.la'</TT> will contain no objects.
</P><P>

Back in the toplevel project directory, all of the preceding objects are
combined by another <TT>`Makefile.am'</TT>:
</P><P>

<TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>
</pre></td></tr></table></P><P>

The initial <SAMP>`SUBDIRS'</SAMP> macro is necessary to ensure that the
libraries in the subdirectories are built before the final library and
executable in this directory.
</P><P>

Notice that I have not listed <TT>`error.h'</TT> in
<SAMP>`liberror_la_SOURCES'</SAMP> this time, since <TT>`liberror.la'</TT> is an
installed library, and <TT>`error.h'</TT> defines the public interface to
that library.  Since the <TT>`liberror.la'</TT> Libtool library is
installed, I have used the <SAMP>`-version-info'</SAMP> option, and I have
also used <SAMP>`-no-undefined'</SAMP> so that the project will compile on
architectures which require all library symbols to be defined at link
time -- the reason <CODE>program_name</CODE> is maintained in
<TT>`liberror'</TT> rather than <TT>`main.c'</TT> is so that the library does
not have a runtime dependency on the executable which links it.
</P><P>

The key to this example is that by linking the <TT>`libreplace.la'</TT> and
<TT>`library.la'</TT> convenience libraries into <TT>`liberror.la'</TT>, all of
the objects in both convenience libraries are compiled into the single
installed library, <TT>`liberror.la'</TT>.  Additionally, all of the
inter-library dependencies of the convenience libraries (<SAMP>`-lm'</SAMP>,
from <TT>`library.la'</TT>) are propagated to <TT>`liberror.la'</TT>.
</P><P>

<BLOCKQUOTE>
A common difficulty people experience with Automake is knowing when to
use a <SAMP>`LIBADD'</SAMP> primary versus a <SAMP>`LDADD'</SAMP> primary.  A useful
mnemonic is: <STRONG><SAMP>`LIBADD'</SAMP> is for ADDitional LIBrary objects.
<SAMP>`LDADD'</SAMP> is for ADDitional linker (LD) objects.</STRONG>
</BLOCKQUOTE>
<P>

The executable, <TT>`convenience'</TT>, is built from <TT>`main.c'</TT>, and
requires only <TT>`liberror.la'</TT>.  All of the other implicit
dependencies are encoded within <TT>`liberror.la'</TT>.  Here is
<TT>`main.c'</TT>:
</P><P>

<TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>
</pre></td></tr></table></P><P>

The only file that remains before you can compile the example is
<TT>`configure.in'</TT>:
</P><P>

<TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>
</pre></td></tr></table></P><P>

There are checks for all of the features used by the sources in the
project: <TT>`math.h'</TT> and either <TT>`string.h'</TT> or <TT>`strings.h'</TT>;
the existence of <CODE>strrchr</CODE> (<EM>after</EM> the tests for string
headers); adding <TT>`basename.o'</TT> to <SAMP>`LIBOBJS'</SAMP> if there is no
system implementation; and the shell code to set <SAMP>`LTLIBOBJS'</SAMP>.
</P><P>

With all the files in place, you can now bootstrap the project:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=smallexample><FONT SIZE=-1><pre>$ ls -R
.:
Makefile.am  configure.in  error.c  error.h  lib  main.c  replace

lib:
Makefile.am  source.c  source.h

replace:
Makefile.am  basename.c
$ aclocal
$ autoheader
$ automake --add-missing --copy
automake: configure.in: installing ./install-sh
automake: configure.in: installing ./mkinstalldirs
automake: configure.in: installing ./missing
configure.in: 7: required file ./ltconfig not found
$ autoconf
$ ls -R
.:
Makefile.am   config.h.in   error.c     ltconfig   mkinstalldirs
Makefile.in   config.sub    error.h     ltmain.sh  replace
aclocal.m4    configure     install-sh  main.c
config.guess  configure.in  lib         missing

lib:
Makefile.am  Makefile.in  source.c  source.h

replace:
Makefile.am  Makefile.in  basename.c
</FONT></pre></td></tr></table></P><P>

With these files in place, the package can now be configured:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=smallexample><FONT SIZE=-1><pre>$ ./configure
...
checking how to run the C preprocessor... gcc -E
checking for math.h... yes
checking for string.h... yes
checking for strrchr... yes
checking for basename... yes
updating cache ./config.cache
creating ./config.status
creating replace/Makefile
creating lib/Makefile
creating Makefile
creating config.h
</FONT></pre></td></tr></table></P><P>

Notice that my host has an implementation of <CODE>basename()</CODE>.
</P><P>

Here are the highlights of the compilation itself:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=smallexample><FONT SIZE=-1><pre>$ make
Making all in replace
make[1]: Entering directory /tmp/replace
/bin/sh ../libtool --mode=link gcc  -g -O2  -o libreplace.la
rm -fr .libs/libreplace.la .libs/libreplace.* .libs/libreplace.*
ar cru .libs/libreplace.al
ranlib .libs/libreplace.al
creating libreplace.la
(cd .libs &#38;&#38; rm -f libreplace.la &#38;&#38; ln -s ../libreplace.la \
libreplace.la)
make[1]: Leaving directory /tmp/replace
</FONT></pre></td></tr></table></P><P>

Here the build descends into the <TT>`replace'</TT> subdirectory and creates
<TT>`libreplace.la'</TT>, which is empty on my host since I don't need an
implementation of <CODE>basename()</CODE>:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=smallexample><FONT SIZE=-1><pre>Making all in lib
make[1]: Entering directory /tmp/lib
/bin/sh ../libtool --mode=compile gcc -DHAVE_CONFIG_H  -I. -I. \
-g -O2 -c source.c
rm -f .libs/source.lo
gcc -DHAVE_CONFIG_H -I. -I. -g -O2 -c -fPIC -DPIC source.c \
-o .libs/source.lo
gcc -DHAVE_CONFIG_H -I. -I. -g -O2 -c source.c \
-o source.o &#62;/dev/null 2&#62;&#38;1
mv -f .libs/source.lo source.lo
/bin/sh ../libtool --mode=link gcc  -g -O2  -o library.la source.lo -lm
rm -fr .libs/library.la .libs/library.* .libs/library.*
ar cru .libs/library.al source.lo
ranlib .libs/library.al
creating library.la
(cd .libs &#38;&#38; rm -f library.la &#38;&#38; ln -s ../library.la library.la)
make[1]: Leaving directory /tmp/lib
</FONT></pre></td></tr></table></P><P>

Next, the build enters the <TT>`lib'</TT> subdirectory to build
<TT>`library.la'</TT>.  The <TT>`configure'</TT> preprocessor macros are passed
on the command line, since no <TT>`config.h'</TT> was created by
<CODE>AC_CONFIG_HEADER</CODE>:
</P><P>

Here, <TT>`main.c'</TT> is compiled (not to a Libtool object, since it is
not compiled using <CODE>libtool</CODE>), and linked with the
<TT>`liberror.la'</TT> Libtool library:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=smallexample><FONT SIZE=-1><pre>gcc -DHAVE_CONFIG_H -I. -I.  -I./lib  -g -O2 -c main.c
/bin/sh ./libtool --mode=link gcc  -g -O2  -o convenience  main.o \
liberror.la
gcc -g -O2 -o .libs/convenience main.o ./.libs/liberror.so -lm \
-Wl,--rpath -Wl,/usr/local/lib
creating convenience
make[1]: Leaving directory /tmp/convenience
</FONT></pre></td></tr></table></P><P>

<CODE>libtool</CODE> calls <CODE>gcc</CODE> to link the <CODE>convenience</CODE>
executable from <TT>`main.o'</TT> and the shared library component of
<TT>`liberror.la'</TT>.  <CODE>libtool</CODE> also links with <SAMP>`-lm'</SAMP>, the
propagated inter-library dependency of the <TT>`library.la'</TT> convenience
library.  Since <TT>`libreplace.la'</TT> and <TT>`library.la'</TT> were
convenience libraries, their objects are already present in
<TT>`liberror.la'</TT>, so they are not listed again in the final link line
-- the whole point of convenience archives.
</P><P>

This just shows that it all works:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=smallexample><FONT SIZE=-1><pre>$ ls
Makefile      config.h       configure.in  install-sh   main.c
Makefile.am   config.h.in    convenience   lib          main.o
Makefile.in   config.log     error.c       liberror.la  missing
aclocal.m4    config.status  error.h       libtool      mkinstalldirs
config.cache  config.sub     error.lo      ltconfig     replace
config.guess  configure      error.o       ltmain.sh
$ libtool --mode=execute ldd convenience
        liberror.so.0 =&#62; /tmp/.libs/liberror.so.0 (0x40014000)
        libm.so.6 =&#62; /lib/libm.so.6 (0x4001c000)
        libc.so.6 =&#62; /lib/libc.so.6 (0x40039000)
        /lib/ld-linux.so.2 =&#62; /lib/ld-linux.so.2 (0x40000000)
$ ./convenience
cos (0) =&#62; 1
lt-convenience: ERROR: This program does nothing!
</FONT></pre></td></tr></table></P><P>

Notice that you are running the uninstalled executable, which is in
actual fact a wrapper script, See section <A HREF="autobook_79.html#SEC79">10.5 Executing Uninstalled Binaries</A>.
That is why you need to use <CODE>libtool</CODE> to run <CODE>ldd</CODE> on
the real executable.  The uninstalled executable called by the wrapper
script is called <CODE>lt-convenience</CODE>, hence the output from
<CODE>basename()</CODE>.
</P><P>

Finally, you can see from the output of <CODE>ldd</CODE>, that
<CODE>convenience</CODE> really isn't linked against either
<TT>`library.la'</TT> and <TT>`libreplace.la'</TT>.
</P><P>

<A NAME="A Large GNU Autotools Project"></A>
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<FONT SIZE="-1">
This document was generated
by <I>Gary V. Vaughan</I> on <I>September, 12  2004</I>
using <A HREF="http://www.mathematik.uni-kl.de/~obachman/Texi2html
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