Makefile: target with pattern does not work

Question

My Makefile looks like this:

BIN = bin OBJECTS = object1.o \ object2.o \ object3.o HDR = $(OBJECTS:%.o=%.h) header1.h header2.h MAIN = main.c CC = gcc CFLAGS = -Wall -g -std=c99 -fstack-protector-all LDFLAGS = -lpthread $(BIN): $(OBJECTS) $(MAIN) $(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ %.o: %.c $(HDR) $(CC) $(CFLAGS) -c $< -o $@

It seems that the %.o: %.c $(HDR) rule is not used. When invoking with option make -r it says that there's no rule to make target object.o. The build of each object file should depend on every header file. What am I missing?

Edit: I should mention that when doing echo $(HDR) than it looks like the variable contains the right values: object1.h object2.h object3.h header1.h header2.h

Could you try make -d object.o, and look at the last twenty lines or so? — Beta
– Beta, Commented Oct 4, 2011 at 0:34

fluffy · Accepted Answer · 2011-10-03 22:23:16Z

2

In the declaration of HDR, try $(OBJECTS:.o=.h) instead. Or, better yet, use gcc -MM or the like to generate your dependencies instead.

answered Oct 3, 2011 at 22:23

fluffy

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3 Comments

fluffy Over a year ago

Hm, okay, I have no idea what's going on then. But still, manual dependency management is kind of a bad idea, and you should look into gcc -MM to generate a .depend file or the like (see the link in my answer).

Scolytus Over a year ago

I just edited my question to mention that HDR (seems to) contains the correct values.

fluffy Over a year ago

Okay, I have no idea what's going on here. It's still a good idea in general to use automatic dependency generation. Jonathan Leffler's answer seems more plausible.

Jonathan Leffler · Accepted Answer · 2011-10-03 23:18:31Z

2

A pattern rule can't have auxilliary dependencies like ${HDR}.

Use:

%.o : %.c $(CC) $(CFLAGS) -c $< -o $@ ${OBJECTS}: ${HDR}

answered Oct 3, 2011 at 23:18

Jonathan Leffler

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2 Comments

eriktous Over a year ago

That's not what the GNU make manual says: gnu.org/software/make/manual/make.html#Pattern-Intro

Scolytus Over a year ago

Indeed the problem seems to be the $(HDR). When stating the prerequisites explicitly, like "%.o: %.c header1.h header2.h ..." it seems to work.

Scolytus · Accepted Answer · 2011-10-04 09:44:21Z

Ok, the given Makefile should work, I had a typo in one of the header file names.

It's a pitty, but make doesn't warn about that. It seems that when a pattern based rule is missing a prerequisite than it's just ignored. The built-in .o creation rule is used instead.

Jonathan Leffler's proposal of ${OBJECTS}: ${HDR} brought that up, because than there's an error regarding "no rule to make target misspelled.h" - I would have expected that from my rule too.

So I can just agree to fluffy, it's better to use auto-generated dependencies instead.

That's a feature. You can have more than one implicit rule rule that fits a target, and the first one whose prerequisites exist (or can be built) is the one Make uses.

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