Make Depend

[Gert Cuykens]

On Sun, 28 Nov 2004 18:57:51 +0100, Gert Cuykens <gert.cuykens at gmail.com> wrote:
> On Sat, 27 Nov 2004 15:44:52 -0500 (EST), John Mills
> 
> 
> <johnmills at speakeasy.net> wrote:
> > Freebies -
> >
> >
> >
> > On Sat, 27 Nov 2004, Conrad J. Sabatier wrote:
> >
> > > On Sat, 27 Nov 2004 09:43:17 +0100, Gert Cuykens
> > > <gert.cuykens at gmail.com> wrote:
> > >
> > > > "A Makefile rule that typically scans all C/C++ source files in a
> > > > directory, and generates rules that indicate that an object file
> > > > depends on certain header files, and must be recompiled if they are
> > > > recompiled."
> > > >
> > > > i dont understand this. how can a object depend on something that is
> > > > not compiled yet? Would the freebsd world not be a happier place if
> > > > make did the dependancy thingies what ever they are automatically ?
> >  ...
> >
> >
> > > Re: dependencies, it should be simple to understand if you give it a
> > > moment's thought.  Let's say you have a file "main.c" that calls
> > > functions in "foo.c".  In order for main.c to compile and link properly
> > > to create a complete, executable program, it's absolutely essential that
> > > foo.c be compiled and linked in as well.
> >
> > > What Makefile dependencies are about is ensuring that, if a change is
> > > made to foo.c, it will be recompiled and relinked with main.c to
> > > guarantee that the final executable is up to date in all respects.
> >
> > Certainly a sensible point, but not the way I understood 'makedepend' to
> > work.
> >
> > As Conrad said, 'make' can be directed to compare the currency of the
> > files upon which a particular product file (compiled object, library,
> > executable, or other type) depends, so that all product files for which
> > the components have changed _are_ rebuilt, but a maximum number of product
> > files (i.e., unchanged objects being linked into a library) are
> > unnecessarily rebuilt. Many of these rules I put in manually.
> >
> > 'make' only knows some 'generic' rules (what is done to change a *.c into
> > a *.o, for example), plus the explicit dependencies I have written into my
> > Makefile. 'makedepend' is a way to automatically generate the
> > file-specific rules that can be deduced from a [source] file's own
> > contents: usually those secondary files that are brought into it by
> > '#include' pragmas. These auxiliary rules are written onto the Makefile
> > and become part of it. These files are not necessarily separately
> > compiled; I find your definition a bit misleading on this.
> >
> > 'makedepend' is given a list of files to scan, and places to look for
> > included files. My 'depend' rule looks like this:
> >
> > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > depend:
> >         makedepend -- $(CFLAGS) -- $(SRCS) -- $(INCLUDES)
> >
> > # DO NOT DELETE THIS LINE -- make  depend  depends  on it.
> >
> > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >
> > That funky last line really tells 'makedepend' where it should write the
> > new rules onto my Makefile. Before using a Makefile on a group of sources,
> > or when source files are added to the build, I remove all the generate
> > rules which have been added below the '# DO NOT DELETE ...' line and
> > rebuild the 'depend' target - which is the Makefile itself:
> >
> >  $ make depend
> >
> > Typical rules automagically added by 'makedepend' are:
> >
> > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > ...
> > BufRing.o: ../Llcommon/SEBase.h StdAfx.h BufRing.h
> > Camera.o: ../Llcommon/SEBase.h StdAfx.h ../Llcommon/commonStruct.h
> > Camera.o: ../Llcommon/secureeye.h ../Llcommon/memCtrl.h
> > Camera.o: ../Llcommon/retCodes.h ../Llcommon/LiveShare.h Camera.h
> > Camera.o: ../Llcommon/Common.h Pump.h BufRing.h CamData.h Snap.h INet.h
> > Camera.o: Player.h
> > INet.o: ../Llcommon/SEBase.h StdAfx.h /usr/include/stdlib.h
> > ...
> > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >
> > The effect of these added rules is that if I change [say] 'BufRing.h' then
> > do 'make all', 'BufRing.c' and 'Camera.c' would be recompiled, but not
> > necessarily 'INet.c'
> >
> > 'make' isn't very bright, but (like 'cpp') it can be _very_ handy.
> >
> >  - John Mills
> >    john.m.mills at alum.mit.edu
> >
> >
 
 so we have some machine code A  from a compiled object file and we
 have machine code B from a other compiled object file. While A is
 running it points to B to do some stuff.
 
 so if i understand it right without make depend we would had to
 recompile A and B if A needed some source changes. with make depend we
 only need to recompile A
 
that also means make depend is only a shortcut, if i dont use make
depend and just do make it will just compile everything right ?