Makefile with different compiler flags for source files

Question

How do I use different compiler flags for different source files in a Makefile? For example, I'd like a Makefile that will produce:

g++ -c -COMPILER_FLAGS_1   -g source1.cpp -o source1.o

g++ -c -COMPILER_FLAGS_2   -g source2.cpp -o source2.o
g++ -c -COMPILER_FLAGS_2   -g source3.cpp -o source3.o
g++ -c -COMPILER_FLAGS_2   -g source4.cpp -o source4.o

g++ -c -COMPILER_FLAGS_3   -g source5.cpp -o source5.o
g++ -c -COMPILER_FLAGS_3   -g source6.cpp -o source6.o
g++ -c -COMPILER_FLAGS_3   -g source7.cpp -o source7.o

g++ -g -o output source1.o source2.o source3.o source4.o source5.o source6.o source7.o 

At the moment I've got about 20 source files (and that's expected to grow), so an easy to maintain file would be nice.

Thanks in advance.

Answer 1

You could do something like the following (untested, so the syntax might be slightly off):

OBJS_1 := source1.o
OBJS_2 := source2.o source3.o source4.o
OBJS_3 := source5.o source6.o source7.o

OBJS := $(OBJS_1) $(OBJS_2) $(OBJS_3)

output: $(OBJS)
    $(CXX) -g -o $@ $^

$(OBJS_1): CXXFLAGS := $(COMPILER_FLAGS_1)
$(OBJS_2): CXXFLAGS := $(COMPILER_FLAGS_2)
$(OBJS_3): CXXFLAGS := $(COMPILER_FLAGS_3)

$(OBJS): %.o: %.cpp
    $(CXX) -c $(CXXFLAGS) -g $< -o $@