Managing Dependency Complexity in Make Files

Question

I am working on my first open source C++ project: https://github.com/jehugaleahsa/spider-cpp.

I am managing my own Makefile and I have "best practices" question regarding how to manage dependencies. Right now, I make each .o file dependent on each of the included header files in the .cpp file. So:

code.o: code.cpp code.hpp dep1.hpp de2.hpp
    g++ -c code.cpp

First of all, I am pretty sure Make supports a shorthand for creating object files. If someone would show an example of this, I'd appreciate it.

Next, is there a way to avoid listing every included header as a dependency? I want to make sure if I change a dependency, that the changes are still compatible. Listing the included headers is tedious and easy to mess up.

Answer 1

OP:

First of all, I am pretty sure Make supports a shorthand for creating object files. If someone would show an example of this, I'd appreciate it.

From here:

OBJS := foo.o bar.o

#Your program should have the objects as dependencies, and link them
proggie: $(OBJS)
gcc $(OBJS) -o proggie


# compile
%.o: %.c
    gcc -c $(CFLAGS) $*.c -o $*.o

OP:

Next, is there a way to avoid listing every included header as a dependency

Lower down on the same page, see these lines:

# pull in dependency info for *existing* .o files
-include $(OBJS:.o=.d)


# compile and generate dependency info
%.o: %.c
    gcc -c $(CFLAGS) $*.c -o $*.o
    gcc -MM $(CFLAGS) $*.c > $*.d

Basically what this does is use gcc's -MM option to obtain a list of header files, and now we can depend on them. Thus we output a file with a list of such header files to a .d file, and then next time, we add the list of files as a dependency, which is what the -include command does. The "-" avoids error if the dependency .d files don't exist yet.

Note, you should modify the above to account for .cpp files

Answer 2

Yes, make supports shorthand for creating object files. This is called rules. And yes, there is a way to avoid listing every included header as a dependency. g++/gcc has -MM option which will generate the full list of dependencies.

Unfortunately, there is no simple explanation on how to do it which I could put here.. You have to read docs and play with make utility. I found this book very helpful: "Managing Projects with GNU Make". There is a doc on GNU site but I found it a bit harder to read. www.gnu.org/software/make/manual/make.html