Makefile auto-dependency generation

Question

I am trying to see auto generated dependency the makefile is below:

 OBJS := main.o 
 run : $(OBJS)
 $(CC) $(OBJS) -o run -lstdc++
 -include $(OBJS:.o=.d)
 %.o : %.cpp
 $(CC) -c $(CFLAGS) $*.cpp -o $*.o
 %.d : %.cpp
 @set -e; rm -f $@; \
 $(CC) -M $(CPPFLAGS) $< > $@.$$$$; \
 echo "creating dependency file."; \
 sed 's,\($*\)\.o[ :]*,1円.o $@ : ,g' < $@.$$$$ > $@; \
 rm -f $@.$$$$
 # remove compilation products
 clean :
 rm -f run *.o *.d*

But the makefile generate a huge list of dependency in main.d but the actual needed is the first few lines. So where I am getting wrong?

• Etan Reisner: What contents are in main.d that you don't think belong there?
• Abhijatya Singh: main.o main.d : main.cpp main.h \ ** /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/iostream \ /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/x86_64-redhat-linux/bits/c++config.h \ /usr/include/bits/wordsize.h \ /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/x86_64-redhat-linux/bits/os_defines.h \ /usr/include/features.h /usr/include/sys/cdefs.h \** Ideally it should show only first line (main.o main.d : main.cpp main.h) . Why the remaining lines are comming and the output expected was main.o: main.cpp main.h?
• Etan Reisner: Your code is clearly including some of them as well (and they are including the other headers). The prerequisites can't stop at the first-level included header files or they will miss things. Is that ** literal?
• Abhijatya Singh: Then how to get the desired output?
• Etan Reisner: Do it manually if you really care about not having the extra information there. But the point is that extra information is correct and you don't ever need to care about it.

Answer 1

Try this instead:

 OBJS := main.o 
 run : $(OBJS)
 $(CC) $(OBJS) -o run -lstdc++
 -include $(OBJS:.o=.d)
 %.o : %.cpp
 $(CC) -c -MMD -MP $(CFLAGS) $*.cpp -o $*.o
 # remove compilation products
 clean :
 rm -f run *.o *.d*