Austin Hyde Austin Hyde - 2 months ago 9
C++ Question

Can I compile all .cpp files in src/ to .o's in obj/, then link to binary in ./?

My project directory looks like this:

/project
Makefile
main
/src
main.cpp
foo.cpp
foo.h
bar.cpp
bar.h
/obj
main.o
foo.o
bar.o


What I would like my makefile to do would be to compile all
.cpp
files in the
/src
folder to
.o
files in the
/obj
folder, then link all the
.o
files in
/obj
into the output binary in the top-level folder
/project
.

I have next to no experience with Makefiles, and am not really sure what to search for to accomplish this.

Also, is this a "good" way to do this, or is there a more standard approach to what I'm trying to do?

Answer

Makefile part of the question

This is pretty easy, unless you don't need to generalize try something like the code below (but replace space indentation with tabs near g++)

CPP_FILES := $(wildcard src/*.cpp)
OBJ_FILES := $(addprefix obj/,$(notdir $(CPP_FILES:.cpp=.o)))
LD_FLAGS := ...
CC_FLAGS := ...

main.exe: $(OBJ_FILES)
   g++ $(LD_FLAGS) -o $@ $^

obj/%.o: src/%.cpp
   g++ $(CC_FLAGS) -c -o $@ $<

Automatic dependency graph generation

A "must" feature for most make systems. With GCC in can be done in a single pass as a side effect of the compilation by adding -MMD flag to CC_FLAGS and -include $(OBJFILES:.o=.d) to the end of the makefile body:

CC_FLAGS += -MMD
-include $(OBJFILES:.o=.d)

And as guys mentioned already, always have GNU Make Manual around, it is very helpful.