Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!necntc!custom!boykin
From: boykin@custom.UUCP (Joseph Boykin)
Newsgroups: comp.unix.questions,comp.unix.wizards
Subject: Re: Strange makefile construct
Message-ID: <781@custom.UUCP>
Date: Fri, 4-Sep-87 12:20:02 EDT
Article-I.D.: custom.781
Posted: Fri Sep  4 12:20:02 1987
Date-Received: Sat, 5-Sep-87 18:23:25 EDT
References: <1162@nrcvax.UUCP>
Organization: Custom Software Systems; Natick, MA
Lines: 39
Summary: $(?:.o=.c) is a macro substitution sequence
Xref: mnetor comp.unix.questions:3884 comp.unix.wizards:4084

In article <1162@nrcvax.UUCP>, chris@nrcvax.UUCP (Chris Grevstad) writes:
> I was looking at some source that came across the net some time ago and
> ran across a very strange construct in the makefile.  It appears that this
> makefile is targeted for a SYSV system and I am familiar only with 4.2BSD
> make.
> 
> This is the weirdness:
> 
> target: file1.o file2.o file3.o file4.o
> 	$(CC) $(CFLAGS) $(?:.o=.c)
> 
> Any suggestions? [....]
> 
> My interpretation says:
> 	This:
> 		$(CC) $(CFLAGS) $(?:.o=.c)
> 	becomes this:
> 		$(CC) $(CFLAGS) file1.c file2.c file3.c file4.c

You're correct, except for one caveat. Here's what the PC/MAKE
documenation says about this:

	"The sequence :string1=string2 is a substitution
	sequence.  All occurrences of string1 which appear
	prior to a blank or tab are replaced by string2.  For
	example, substitute .c for all occurrences of .obj in the
	macro OBJECTS:
		$(OBJECTS:.obj=.c)

In the example you have, $(?.o=.c) will generate files with a .c
extension from those dependencies which were found to be newer
than the target.  The problem with this particular command is
that 'target' may now be compiled with only three (or less) files
instead of all four if one or more of the .o files was not modified;
given the command, this may cause an error.

Joe Boykin
Custom Software Systems
...necntc!custom!boykin