Makefile与Windows资源文件的循环依赖

Question

There have been several questions regarding circular dependencies being dropping when running a Makefile ( here and here ), however, I am still a bit confused as to why they are occurring.

For example, I am trying to compile a Win32 GUI program that contains resource files ( from this tutorial ). These resource files are compiled to object files through the windres command, so they can be linked to the final executable ( as described here ):

CC = gcc
CFLAGS = -mwindows
DEPS = resource.h
OBJ = menu_one.o $(patsubst %.rc,%.rc.o,$(wildcard *.rc))

all: menu_one

%.rc.o: %.rc
    windres $^ -o $@

%.o: %.c $(DEPS)
    $(CC) -c $< -o $@ $(CFLAGS)

menu_one: $(OBJ)
    $(CC) $^ -o $@ $(CFLAGS)

The command $(patsubst %.rc,%.rc.o,$(wildcard *.rc)) takes all the resource files ending in .rc and slaps a .o extension onto them (eg resource.rc.o ).

When I run this, everything seems to work and I get a working executable, however, Make outputs the following:

gcc -c menu_one.c -o menu_one.o -mwindows
make: Circular menu_one.rc <- menu_one.rc.o dependency dropped.
windres menu_one.rc -o menu_one.rc.o
gcc menu_one.o menu_one.rc.o -o menu_one -mwindows

Is this circular dependency occurring because I technically have two .o rules? In other words, how can I correct this circular dependency?

---

Edit 1:

I tried following what @MadScientist said, however, this still created a circular dependency with Make. After some more Googling, I came across the following page . Towards the very bottom there is a section titled " Circular File Dependencies ." This got me thinking about the output from Make:

make: Circular menu_one.rc <- menu_one.rc.o dependency dropped.

It looks to be that the rc suffix is creating this dependency - even though it is not part of the file extension of the outputted object file (ie file.rc.o ). If I change the output file suffix to be .res.o , the circular dependency goes away entirely:

...
RESOBJ = $(patsubst %.rc,%.res.o,$(wildcard *.rc))
OBJ = menu_one.o $(RESOBJ)
...
%.res.o: %.rc
    windres $^ -o $@
...

This sparks a very similar question, if I wanted to use the previous suffix .rc.o , how would you accomplish this? Is it possible?

Edit 2:

@MadScientist 's suggestion of using a match-anything rule worked perfectly with correcting the problem. This now allows me to use the .rc.o suffix ending. See @MadScientist 's updated answer below.

Answer 1

One way is to not name your windres output files with a .o extension. If you choose a different extension, you won't have this problem.

Another way is to use static pattern rules for the windres targets:

RCOBJ := $(patsubst %.rc,%.rc.o,$(wildcard *.rc))
OBJ = menu_one.o $(RCOBJ)

  ...
$(RCOBJ) : %.rc.o : %.rc
        windres $^ -o $@

Since static pattern rules are shorthand for creating explicit rules, and are not implicit rules, they don't participate in searches so make won't come up with a circular dependency.

ETA

OK I created your example locally. Using make -d we can see what happens: make needs to build menu_one.rc.o and it finds our rule with a prerequisite of menu_one.rc . Then it needs to see if it can rebuild manu_one.rc , and it find the generic pattern rule for building executables:

%: %.o ; ...

Matching this pattern with a target of menu_one.rc gives a prerequisite of menu_one.rc.o , and you have a loop.

What you need to do is notify make that the *.rc files are source files and make shouldn't try to build them. You can do this by declaring a terminal rule . There is a comprehensive discussion of the intricacies of dealing with match-anything rules (rules with a target of % alone, which matches any target) in the GNU make manual.

Add this to inform make that your .rc files are terminal (that is, they can't be built from something else):

%.rc: