Re: AC_CONFIG_HEADERS vs. AC_CONFIG_FILES

[Ralf Corsepius]

On Sat, 2005-12-17 at 22:16 -0500, David Fang wrote:
> > >   What I'd like is AC_CONFIG_FILES to also perform a difference
> > > check on the output files before overwriting them, just the way
> > > AC_CONFIG_HEADERS does.  (Is this a safe and easy request to accommodate?)
> >
> > Maybe you can have an intermediate file created from config.status
> > (AC_CONFIG_FILES), and then use move-if-change to the header, in
> > conjunction with a stamp file.  I'm not sure whether there are make
> > implementations that don't cope well with this scheme, nor whether
> > that is due to bugs in them.
> 
> Hi,
>       I tried my own AC_CONFIG_FILES like this:
> 
> AC_CONFIG_FILES([foo.h:foo.h.in],
> [
>       dnl ... create foo.h.tmp from foo.h.in
>       dnl ... move-if-change foo.h.tmp foo.h
> ]
> )
> 
> However, the configure process would always *first* clobber
> foo.h from foo.h.in before executing any of my own commands,

Have you tried

AC_CONFIG_FILES([foo.h.tmp:foo.h.in]),
  [
    move-if-change foo.h.tmp foo.h 
  ])


Another approach would be "to do everything by yourself" in your
configure.ac. I am using a construct similar to this, in one configure
script (Very shortened, the real world code is much more larger):

# Create cpuopts.h using echo, cat etc.
...
echo "#ifndef ...." > cpuopts.tmp
echo "#define bar 1" >> cpuopts.tmp
...

AS_MKDIR_P(foo)
AS_IF([test -f foo/cpuopts.h],
[
  AS_IF([cmp -s foo/cpuopts.h cpuopts.tmp 2>/dev/null],
  [
    AC_MSG_NOTICE([foo/cpuopts.h is unchanged])
    rm -f cpuopts.tmp
  ],[
    AC_MSG_NOTICE([creating foo/cpuopts.h])
    rm -f foo/cpuopts.h
    mv cpuopts.tmp foo/cpuopts.h
  ])
],[
    AC_MSG_NOTICE([creating foo/cpuopts.h])
    rm -f foo/cpuopts.h
    mv cpuopts.tmp foo/cpuopts.h
])

Basically, what I am doing is to create a file (here cpuopts.tmp) in
configure.ac using standard /bin/sh tools (echo, cat and
"here"-documents) and then to update foo/cpuopts.h mimicking the
"move-if-change"-logic as internally being used for AC_CONFIG_HEADERS
inside of autoconf.

Ralf