Question

I am new to makefiles and facing some issue with it. I have created the following makefile. It works correctly. But when I modify the main.cpp and run make, it says “everything is up to date”. I need to do a make clean and run make again, everything will work.

Looks like there is some issue with this makefile and I can’t figure it out where it is going wrong. Can anyone help me to find out where is the error in this makefile and why it is not building changed files?

#Main makefile which does the build

CFLAGS =
CC = g++
PROG = fooexe

#each module will append the source files to here
SRC :=

#including the description
include foo/module.mk

OBJ := $(patsubst %.cpp, %.o, $(filter %.cpp,$(SRC))) main.o

#linking the program
fooexe: $(OBJ)
    $(CC) -o $(PROG) $(OBJ)

%.o:
    $(CC) -c $(SRC) -o $(patsubst %.cpp, %.o, $(filter %.cpp,$(SRC)))

main.o:
    $(CC) -c main.cpp

depend:
    makedepend -- $(CFLAGS) -- $(SRC)

.PHONY:clean
clean:
    find . -name "*.o" | xargs rm -vf
    rm -vf fooexe

Answer 1

Normally the .o file needs to have a dependency on the corresponding .cpp file. I think this is the syntax, but not 100% sure:

%.o : %.cpp
    $(CC) ...

main.o : main.cpp
    $(CC) ...