Re: help setting LDFLAGS and CFLAGS within AC_ARG_ENABLE

[Ralf Wildenhues]

Hi Patrick,

* J. Patrick Bedell wrote on Fri, Aug 19, 2005 at 03:52:17AM CEST:
>       I am trying to modify the configure.in file of a pre-existing 
> project (CVS) to include a CFLAGS and LDFLAGS addition when I find the 
> libraries I'm looking for.  The content of the addition that I am making 
> is derived from a shell command, namely 'xmlsec1-config --cflags' and
> 'xmlsec1-config --libs'.  I'm trying to use the following in configure.in 
> to make the modification to CFLAGS and LDFLAGS in the compilation process, 
> but it's not working at all. :(  How would I include in the AC_ARG_ENABLE 
> macro a modification to the global CFLAGS and LDFLAGS variables?

A few comments to your code: (I have not looked thoroughly, it might not
solve all issues with it)

> AC_ARG_ENABLE(
>   [certification],
>   AC_HELP_STRING(
>     [--enable-certification],
>     [Include code for interfacing to an information currency server. 
>     (default)]), ,
>   [enable_certification=yes])
> 
> if test no != "$enable_certification"; then

I'd write
  test Xno != X"$enable_certification"
but I think Autoconf sanitizes the $enable_* variables so that it is not
necessary to do so (`-' is changed to `_').

>  AC_CHECK_HEADERS(openssl/evp.h libxml/tree.h libcsoap/soap-client.h 
>  xmlsec/xmlsec.h,
>   AC_DEFINE(
>     [CERTIFICATION_SUPPORT], [1],
>     [Define if you want CVS to be able to create information currency from 
>     submitted code.])
>     AC_CHECK_LIB(ssl,printf,[LIBS="${LIBS} -lssl"])

You should _not_ check for printf in the ssl library.
Use a function that is defined in libssl.  Preferably one that you use.

Also, in general, you should prepend to LIBS, not append.  Rationale:
the library you check for might depend on other libraries already in
$LIBS.  The order of libraries in $LIBS might be important on other
systems!  (For specific libraries, there might be reasons for the other
way round.)

I see that several examples in the Autoconf manual do this differently.
Below is a proposed patch to fix this.

>     AC_CHECK_LIB(xml2,printf,[LIBS="${LIBS} -lxml2"])
>     AC_CHECK_LIB(xmlsec1,xmlSecCryptoInit,[LIBS="${LIBS} -lxmlsec1"])
>     AC_CHECK_LIB(csoap,printf,[LIBS="${LIBS} -lcsoap"])

Same with these three lines above.

>  CFLAGS=$CFLAGS -g `xmlsec1-config --cflags`;
>  LDFLAGS="$LDFLAGS -g `xmlsec1-config --libs`;

You need more quoting in these two lines.  Also, I would _not_ add "-g".
This is not portable, because some compilers do not allow -g in
combination with optimization.  The AC_PROG_CC macro causes configure to
add "-g -O2" by default for gcc, and either -g or -O2 otherwise, when
they work; in any case, that choice can be overridden by the user
through $CFLAGS.

Then again, I think you should use LIBS, not LDFLAGS.
So, good would be like this:

 CFLAGS="$CFLAGS `xmlsec1-config --cflags`"
 LIBS="`xmlsec1-config --libs` $LIBS"

But now you start to use xmlsec1-config.  I don't know the package, but
I believe this would make some of the other tests you did above
obsolete, at least the check for xmlsec1:
  xmlsec1-config --libs
should give you what you want (unless there exist xmlsec1 libs without
xmlsec1-config).  I'd replace the "AC_CHECK_LIB(xmlsec1,...)" check
with a check for the tool xmlsec1-config.

> )
> fi
> dnl
> dnl end --enable-certification
> dnl

Cheers,
Ralf


        * doc/autoconf.texi (Defining Symbols, Changed Results):
        Prepend to LIBS, not append, in examples.

Index: doc/autoconf.texi
===================================================================
RCS file: /cvsroot/autoconf/autoconf/doc/autoconf.texi,v
retrieving revision 1.925
diff -u -r1.925 autoconf.texi
--- doc/autoconf.texi   6 Jul 2005 21:39:31 -0000       1.925
+++ doc/autoconf.texi   19 Aug 2005 07:39:05 -0000
@@ -7330,7 +7342,7 @@
 
 @example
 AC_CHECK_HEADER([elf.h],
-  [AC_DEFINE([SVR4], [1], [System V Release 4]) LIBS="$LIBS -lelf"])
+  [AC_DEFINE([SVR4], [1], [System V Release 4]) LIBS="-lelf $LIBS"])
 @end example
 
 @noindent
@@ -7339,7 +7351,7 @@
 @example
 AC_CHECK_HEADER([elf.h],
   [AC_DEFINE([SVR4], [1], [System V Release 4])
-   LIBS="$LIBS -lelf"])
+   LIBS="-lelf $LIBS"])
 @end example
 
 @noindent
@@ -7347,7 +7359,7 @@
 
 @example
 AC_CHECK_HEADER([elf.h],
-  [AC_DEFINE([SVR4], [1], [System V Release 4]); LIBS="$LIBS -lelf"])
+  [AC_DEFINE([SVR4], [1], [System V Release 4]); LIBS="-lelf $LIBS"])
 @end example
 
 @node Setting Output Variables
@@ -15340,7 +15352,7 @@
   saved_LIBS="$LIBS"
   for lib in bsd socket inet; do
     AC_CHECKING(for syslog in -l$lib)
-    LIBS="$saved_LIBS -l$lib"
+    LIBS="-l$lib $saved_LIBS"
     AC_HAVE_FUNCS(syslog)
     case "$DEFS" in
     *-DHAVE_SYSLOG*) break ;;
@@ -15359,7 +15371,7 @@
   # syslog is not in the default libraries.  See if it's in some other.
   for lib in bsd socket inet; do
     AC_CHECK_LIB([$lib], [syslog], [AC_DEFINE([HAVE_SYSLOG])
-      LIBS="$LIBS -l$lib"; break])
+      LIBS="-l$lib $LIBS"; break])
   done
 fi
 @end example