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Re: Make rebuilds when it is not necessary
From: |
Paul D. Smith |
Subject: |
Re: Make rebuilds when it is not necessary |
Date: |
Mon, 6 Mar 2006 16:00:45 -0500 |
%% "Rupal Desai" <address@hidden> writes:
rd> $(OBJS):$(OBJDIR)/%.o: %.cpp $(OBJDIR)
This is (at least one of) your problem(s).
You've added OBJDIR as a prerequisite. That means that any time OBJDIR
is newer than the target (xxxx.o), the .o file will be considered out of
date and rebuilt.
Well, on UNIX anyway, a directory's last modified timestamp is changed
whenever the directory is changed, which means whenever a file is added,
removed, or renamed in that directory.
So, every time a .o is created in that directory it becomes newer than
all the .o's that were already there, and they all rebuild.
For this reason it's virtually always a very bad idea to list a
directory as a normal prerequisite of a target.
You have two choices. I personally prefer to simply always create the
directory immediately when make starts, like this:
__dummy := $(shell [ -d "$(OBJDIR)" ] || mkdir -p "$(OBJDIR)")
or similar.
The alternative, if you have a sufficiently new version of GNU make, is
to use order-only prerequisites:
$(OBJS):$(OBJDIR)/%.o: %.cpp | $(OBJDIR)
--
-------------------------------------------------------------------------------
Paul D. Smith <address@hidden> Find some GNU make tips at:
http://www.gnu.org http://make.paulandlesley.org
"Please remain calm...I may be mad, but I am a professional." --Mad Scientist