Create *.o files in a separate folder

Question

I'm trying to make so that the *.o files are kept in /bin however after running it, the *.o files are not kept.

my file systems is as follows:

> bin
> src
    *.cpp
    > headers
        *.h
makefile

.

CC := g++
CFLAGS := -Isrc/headers
NAME := run

SRC := src/
HSRC := $(SRC)/headers/
OBJ := bin/

SOURCES := $(wildcard $(SRC)*.cpp)
DEPS = $(wildcard $(HSRC)*.h)
OBJECTS := $(patsubst $(SRC)*.cpp,$(OBJ)*.o,$(SOURCES))

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

$(NAME): $(OBJECTS)
    $(CC) -o $@ $^ $(CFLAGS)

.PHONY: clean

clean:
    rm -f $(NAME) $(OBJ)/*.o *~ core $(INCDIR)/*~

Beta · Accepted Answer · 2022-10-08 05:13:38Z

Your main, high-level problem is that you are not testing the makefile as you develop it, so the bugs pile up before you know they're there.

The first concrete problem is that your assignment to OBJECTS is incorrect, and doesn't work the way you think it does. The patsubst function uses %, not *, so it ought to be:

OBJECTS := $(patsubst $(SRC)%.cpp,$(OBJ)%.o,$(SOURCES))

The second is that you have not decided whether OBJ should contain a trialing slash. It shouldn't, but that's not the point; the point is that you must be consistent. Look here:

OBJ := bin/

...

$(OBJ)/%.o: %.cpp $(DEPS)
    ...

See the problem? You have written a rule that will match bin//foo.o but not bin/foo.o, so Make will never invoke it. We must pick one convention or the other; for purposes of this Answer I will pick this one:

OBJ := bin

Third, when you wrote that rule you appear to have overlooked the fact that you put the source files in their own directory, so we must modify it:

$(OBJ)/%.o: $(SRC)%.cpp $(DEPS)

There is still some room for improvement, but this will work.

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