Re: Automatically using /usr/local/{include,lib}

[Bob Friesenhahn]

On Mon, 6 Feb 2006, Guillaume Rousse wrote:

> Default LDPATH and CPPFLAGS values are empty, making all AC_LIB_CHECK
> and AC_HEADER_CHECK unable to detect libraries installed under
> /usr/local. Whereas an knowledgeable user will export these variable
> before running ./configure, many other will just be unable to build
> software properly (and some maintainers may even workaround it by
> introducing configure wrappers, I've seen it).

Modern configure also supports these as arguments on the command line 
and the INSTALL documentation file clearly describes how to use them.

> Is there any disadvantage setting default values to thoses variables in
> configure.ac, such as:
> LDFLAGS=-L/usr/local/lib
> CPPFLAGS=-I/usr/local/include

Yes, there are disadvantages and they are not immediately obvious. By 
encoding these defaults, the maintainer is assuming something about 
the user's build environment which may not be correct and may not be 
fixable without manually editing the configure script.

One trick that I use (as end user) is to add a config.site 
(/usr/local/share/config.site by default) to each of my systems 
which provides suitable defaults for that system.  Then if I don't 
provide any overrides, a plain 'configure' just works.  This method 
allows users to establish their own defaults.

Here is an example of a config.site which establishes useful defaults:

# config.site for configure
#

echo 'Applying settings for 32-bit build ...'

# Change some defaults.

test "$prefix" = NONE && prefix=/usr/local

CC_DEFAULT="gcc-4.0.1"
CXX_DEFAULT="c++-4.0.1"
CFLAGS_DEFAULT=-O2
CXXFLAGS_DEFAULT=-O
LDFLAGS_DEFAULT="-L/usr/local/lib -R/usr/local/lib"
LIBS_DEFAULT=

if test "${ac_env_CC_set}" != set
then
  CC="$CC_DEFAULT"
fi

if test "${ac_env_CXX_set}" != set
then
  CXX="$CXX_DEFAULT"
fi

if test "${ac_env_CFLAGS_set}" != set
then
  CFLAGS="$CFLAGS_DEFAULT"
fi

if test "${ac_env_CXXFLAGS_set}" != set
then
  CXXFLAGS="$CXXFLAGS_DEFAULT"
fi

if test "${ac_env_CPPFLAGS_set}" != set
then
  CPPFLAGS="$CPPFLAGS_DEFAULT"
fi

if test "${ac_env_LDFLAGS_set}" = set
then
  LDFLAGS="$LDFLAGS $LDFLAGS_DEFAULT"
else
  LDFLAGS="$LDFLAGS_DEFAULT"
fi

echo "CC       = \"$CC\""
echo "CXX      = \"$CXX\""
echo "CFLAGS   = \"$CFLAGS\""
echo "CXXFLAGS = \"$CXXFLAGS\""
echo "CPPFLAGS = \"$CPPFLAGS\""
echo "LDFLAGS  = \"$LDFLAGS\""

======================================
Bob Friesenhahn
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/