A question about an interesting Makefile

This is a discussion on A question about an interesting Makefile within the Tech Board forums, part of the Community Boards category; I am reading GNU Make's manual, here is an example from it: http://www.cs.utah.edu/dept/old/texi..._toc.html#SEC8 Code: objects = main.o kbd.o command.o display.o ...

  1. #1
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    A question about an interesting Makefile

    I am reading GNU Make's manual, here is an example from it:

    http://www.cs.utah.edu/dept/old/texi..._toc.html#SEC8

    Code:
    objects = main.o kbd.o command.o display.o \
              insert.o search.o files.o utils.o
    
    edit : $(objects)
            cc -o edit $(objects)
    main.o : main.c defs.h
            cc -c main.c
    kbd.o : kbd.c defs.h command.h
            cc -c kbd.c
    command.o : command.c defs.h command.h
            cc -c command.c
    display.o : display.c defs.h buffer.h
            cc -c display.c
    insert.o : insert.c defs.h buffer.h
            cc -c insert.c
    search.o : search.c defs.h buffer.h
            cc -c search.c
    files.o : files.c defs.h buffer.h command.h
            cc -c files.c
    utils.o : utils.c defs.h
            cc -c utils.c
    clean :
            rm edit $(objects)
    It's interesting that main.o depends on defs.h. I don't think it's necessary to put defs.h for main.o . Because if main.o depends on defs.h, you just need to include <defs.h> in main.c, there is no need to put defs.h as a dependent in a Makefile.

    Am I right?

  2. #2
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    I take back my question. Now I understand that claiming:
    main.o : main.c defs.h
    is to let complier know that if defs.h changes, main.o has to be recompiled.
    It has nothing to do with
    g++ -c -o main.o main.c

  3. #3
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    Quote Originally Posted by meili100 View Post
    I take back my question. Now I understand that claiming:
    main.o : main.c defs.h
    is to let complier know that if defs.h changes, main.o has to be recompiled.
    It has nothing to do with
    g++ -c -o main.o main.c
    That is exactly it. You should list all files that the object file depends on, so if your main.c include defs.h, then you need to specify that on the dependencies for main.o. All include files that are part of the project should be specified this way. Gcc has the option "-MM" that will generate a dependency list for the input file(s).

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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