GNU make not detecting if files are changed on windows

Question

I'm a noob with make in general so apologies in advance.

I have a folder structure, where foo.cpp is in the root of the project and all other .cpp files are in one and all headers in another folder. Whenever I change something make just says that everything is up to date.

Working on windows 10.

The code is from

my makefile:

OBJS = foo.o bar.o
CC = g++
INCLUDE_PATHS = -IC:\Mingw_libs\include\SDL2
LIBRARY_PATHS = -LC:\Mingw_libs\lib -Iheaders
COMPILER_FLAGS = -std=c++11
LINKER_FLAGS = -lmingw32 -lSDL2main -lSDL2 -lSDL2_image 

OUTPUTFILE = main

all: $(OBJS)
    $(CC) $(OBJS) $(INCLUDE_PATHS) $(LIBRARY_PATHS) $(LINKER_FLAGS) -o $(OUTPUTFILE)

clean:
    rm *.o
    rm *.exe

foo.o:
    $(CC) -c foo.cpp $(INCLUDE_PATHS) $(COMPILER_FLAGS) $(LIBRARY_PATHS) $(LINKER_FLAGS)

bar.o:
    $(CC) -c sources/bar.cpp $(INCLUDE_PATHS) $(COMPILER_FLAGS) $(LIBRARY_PATHS) $(LINKER_FLAGS)

Answer 1

You should declare target dependencies like that:

foo.obj: foo.c
    ....

Otherwise make will not now wich files to check for changes.

Answer 2

Your makefile has no dependencies for foo.o or bar.o .

This

all: $(OBJS)
    $(CC) $(OBJS) $(INCLUDE_PATHS) $(LIBRARY_PATHS) $(LINKER_FLAGS) -o $(OUTPUTFILE)

says all depends on $(OBJS) . So when one of the files in $(OBJS) changes, that step is run.

This says foo.o depends on nothing:

foo.o:
    $(CC) -c foo.cpp $(INCLUDE_PATHS) $(COMPILER_FLAGS) $(LIBRARY_PATHS) $(LINKER_FLAGS)

You need to add the dependency:

foo.o: foo.cpp
    $(CC) -c foo.cpp $(INCLUDE_PATHS) $(COMPILER_FLAGS) $(LIBRARY_PATHS) $(LINKER_FLAGS)

Note that the spaces after the : usually need to be a tab, not actual space(s).

Answer 3

You need to add dependencies to your target. Make has the syntax

target : prerequisite
    command

So in your case:

foo.o: foo.cpp
    $(CC) -c $< $(INCLUDE_PATHS) $(COMPILER_FLAGS) $(LIBRARY_PATHS) $(LINKER_FLAGS)

same with bar

the $< is a placeholder for the first prerequisite. So you don't have to type foo.cpp twice.

You can checkout more automatic variables here: https://www.gnu.org/software/make/manual/make.html#Automatic-Variables