Linux G++ Makefile (Or C++ Code)

This is a discussion on Linux G++ Makefile (Or C++ Code) within the C++ Programming forums, part of the General Programming Boards category; On my Linux VM I have everything installed correctly and updated properly. I really am new to Makefiles, so before ...

  1. #1
    NOX
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    Linux G++ Makefile (Or C++ Code)

    On my Linux VM I have everything installed correctly and updated properly. I really am new to Makefiles, so before you point me to a tutorial I just need to understand why my code is not compiling.

    Actually, I can make it compile, but what I have to do does not seem right at all. What I do to "fix" this error is make "Queue.o" a dependency in main, but it shouldn't depend on the Queue class...For now it should just depend on the road class...

    Error:
    Code:
    Road.o: In function 'Road::Road(int, int)':
    Road.C: (.text+0x56): undefined reference to 'Queue::Queue(char)'
    Road.o: In function 'Road::Road(int, int)':
    Road.C: (.text+0x86): undefined reference to 'Queue::Queue(char)'
    collect2: ld returned 1 exit status
    make *** [main] Error 1
    Makefile:
    Code:
    CXXFLAGS=-O3
    
    all: main
    
    main: Road.o
    
    Queue.o: Queue.h Vehicle.o
    
    Road.o: Road.h
    
    Vehicle.o: Vehicle.h
    
    clean:
        rm *.o main
    Queue Class Header:
    Code:
    #ifndef _QUEUE_H_
    #define _QUEUE_H_
    
    #include "Vehicle.h"
    #include <cstdlib>
    
    struct QNode;
    
    class Queue{
    public:
        /* CONSTRUCTORS */
        Queue();
    
        /* OBSERVERS */
        bool IsEmpty() const{return pHead==NULL;};
        int  Size() const{return size;};
        void Print() const;
    
        /* TRANSFORMERS */
        void Dequeue();
        void Enqueue(Vehicle * pV);
    
    private:
        QNode * pHead;
        QNode * pTail;
        int     size;
    };
    
    #endif
    Road Class Header:
    Code:
    #ifndef _ROAD_H_
    #define _ROAD_H_
    
    #include "Queue.h"
    
    class Road{
    public:
        /* CONSTRUCTORS */
        Road(int id, int travelTime = (rand() % 20) + 1);
    
        /* OBSERVERS */
        int  GetID() const{return _id;};
        int  GetTravelTime() const{return _travelTime;};
        void Print() const;
    
        /* TRANSFORMERS */
        void AddVehicle();
        void RemoveVehicle();
        void SetID(int newID);
        void SetTravelTime(int newTime);
    
    private:
        Queue _road;
        int   _id;
        int   _travelTime;
    };
    
    #endif

  2. #2
    a_capitalist_story
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    So...how does the Makefile know how to make Road.o? Or any of the other .o files?

  3. #3
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    Your makefile should probably look more like this:
    Code:
    CXXFLAGS=-O3
    
    all: main
    
    main: Road.o
    
    Queue.o: Queue.cpp Vehicle.o
    
    Road.o: Road.cpp
    
    Vehicle.o: Vehicle.cpp
    
    clean:
        rm *.o main
    bit∙hub [bit-huhb] n. A source and destination for information.

  4. #4
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    I disagree with bithub.

    You want the object files to depend on both their associated source files, and their included non library headers.

    You don't want the object files to depend on each other.

    Main should depend on all of the object files.
    It is too clear and so it is hard to see.
    A dunce once searched for fire with a lighted lantern.
    Had he known what fire was,
    He could have cooked his rice much sooner.

  5. #5
    NOX
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    Quote Originally Posted by rags_to_riches View Post
    So...how does the Makefile know how to make Road.o? Or any of the other .o files?
    Quote Originally Posted by bithub View Post
    Your makefile should probably look more like this:
    Code:
    CXXFLAGS=-O3
    
    all: main
    
    main: Road.o
    
    Queue.o: Queue.cpp Vehicle.o
    
    Road.o: Road.cpp
    
    Vehicle.o: Vehicle.cpp
    
    clean:
        rm *.o main
    I was always taught to use the header file (or specification file), because make is "smart" enough to understand that it is in fact just a header file.

    Quote Originally Posted by King Mir View Post
    I disagree with bithub.

    You want the object files to depend on both their associated source files, and their included non library headers.

    You don't want the object files to depend on each other.

    Main should depend on all of the object files.
    Ok, so your talking about modular code then (a.k.a. Code that only depends on itself). But my question would have to be if that Road depends on the Queue (because that all a road is, is a Queue), then why wouldn't I put that as a dependency?

    So pretty much what I am asking is, if Road depends on Queue, then why wouldn't I make it so in the Makefile?

  6. #6
    and the Hat of Guessing tabstop's Avatar
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    It is highly unlikely that Road depends on Queue.o. (I'm assuming here that Road does not contain your main function.) It may well depend on Queue.h. It can call functions that live in Queue.o, which is not at all the same thing as depending on Queue.o.

  7. #7
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    Ok, so your talking about modular code then (a.k.a. Code that only depends on itself). But my question would have to be if that Road depends on the Queue (because that all a road is, is a Queue), then why wouldn't I put that as a dependency?

    So pretty much what I am asking is, if Road depends on Queue, then why wouldn't I make it so in the Makefile?
    Because if Road.cpp uses functions from Queue.cpp, then they are coded as references. The object file does not resolve those references; that's done at the linking stage, when main is built.

    Road.o does need to depend on Queue.h, because it includes that header.
    It is too clear and so it is hard to see.
    A dunce once searched for fire with a lighted lantern.
    Had he known what fire was,
    He could have cooked his rice much sooner.

  8. #8
    NOX
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    Ok, I understand now, thank you very much ^_^

    -NOX

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