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Re: using system getopt_long instead of local version

From: Tim Van Holder
Subject: Re: using system getopt_long instead of local version
Date: Sun, 2 Dec 2001 10:59:57 +0100

> Currently, my has:
> AC_CHECK_FUNC(getopt_long,,
> [LIBS="$LIBS -L./getopt" CFLAGS="$CFLAGS -I./getopt"])

Close, but no cigar.  What is the library's name?

Well, the linker will see something like this:

link -options <objects> -lintl -L./getopt

This obviously does not do what you want, as you don't
specify it should link in libgetopt.a.
Additionally, unless you sources are in '.', using './getopt'
as library search path is a bit suspect.  And I'm not sure you're
supposed to put any linker flags (other than libraries) in
The right way to do it would be to use

[LIBS="$LIBS @builddir@/getopt/libgetopt.a" CFLAGS="$CFLAGS

I think (not sure if LIBS can have substitution variables; if
not, you'd have to use $ac_top_builddir, but that's an internal
If specifying the full library name is not acceptable, you can add
"-lgetopt" to LIBS, and add -L./getopt to LDFLAGS (pretty sure you
can't use substitution variables in LDFLAGS).

Yet another alternative would be to let automake handle it; putting
something like

GETOPT = -L$builddir/getopt -lgetopt

in, and calling AM_CONDITIONAL in should also
do the trick.

Yet another option would be to ditch the library idea, and have do this:

[# This goes directly to the Makefile, so you need $(OBJEXT)
CFLAGS="$CFLAGS -I./getopt"])

In, you'd list the getopt sources in EXTRA_x_SOURCES, so
automake will create rules for them.  And you use @GETOPT_OBJECTS@
in x_LDADD (with x the name of your executable).  This will cause
the list of required objects to only contain the getopt ones if there
is no system getopt.  You may need to keep the header separate so
that it's only used when the local sources are used.

> Also, feel free to point me to any good examples. (I have looked at
> several examples of checking for getopt.h, but they don't do 
> what I want.)

Well, you could look at what libiberty does; it decides what sources
to compile and add to the library based on run-time tests.

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