Destructors and Constructors on classes

This is a discussion on Destructors and Constructors on classes within the C++ Programming forums, part of the General Programming Boards category; Hi. I have a C++ book right in front of me here, and it suggest making a destructor like this: ...

  1. #1
    Politics&Cpp geek Da-Nuka's Avatar
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    Destructors and Constructors on classes

    Hi.
    I have a C++ book right in front of me here, and it suggest making a destructor like this:

    Code:
    class SomeClass {
    public:
    ~SomeClass ();  // Destructor definition
    };
    
    
    SomeClass::~SomeClass () {
    
    }

    But when i do this, exactly like the book says, i get this one:
    Code:
      multiple definition of `SomeClass::~SomeClass()' 
      first defined here 
      ld returned 1 exit status 
      Makefile.win 
     [Build Error]  [YAPI.exe] Error 1
    Looks like it doesent allow me to first define it, and then implement it...
    Is it that this isnt, allowed, and that my C++ book is wrong?

    Or is it a syntax error somewhere?

  2. #2
    Cat without Hat CornedBee's Avatar
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    If you copied this verbatim from the book, then you've got a bad book.

    The comment that says "destructor definition" is wrong. This line is the destructor declaration. The definition is further down, the SomeClass::~SomeClass thing.

    The definition must go into a source file, not a header file. For example, you might have created a pair of files for SomeClass, like SomeClass.h and SomeClass.cpp. The destructor definition goes into SomeClass.cpp, while the class definition (including the destructor declaration) goes into SomeClass.h.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

  3. #3
    Politics&Cpp geek Da-Nuka's Avatar
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    Okay, i have now remade my example:

    SomeClass.h
    Code:
    class SomeClass {
    public:
    ~SomeClass (); 
    };

    SomeClass.cpp
    Code:
    SomeClass::~SomeClass () {
    
    }
    I still get the same error... ideas?

  4. #4
    Deo
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    You do not have to put the code in two seperate files for it to work..

    I often write both my class specification and definition in the .h to make writing easier and then move the definition part to a separate .cpp later.
    As for your error I do not know... thats how I would write it..

    perhaps you should add a constructor implicitly...
    Someclass();
    ~Someclass();

    Though I doubt that is the problem..

  5. #5
    Cat without Hat CornedBee's Avatar
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    You still get the same error? Hmm...

    Are you #include'ing the .cpp file anywhere?
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

  6. #6
    Politics&Cpp geek Da-Nuka's Avatar
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    No, im not including the .cpp file anywhere..
    (but i include the .h file in hte .cpp file, but thats self-explanatory...)


    Could it be my compiler?
    (Dev C++ 4.9.9.2?)

  7. #7
    Cat without Hat CornedBee's Avatar
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    No, but perhaps your compilation process. Have you recompiled every .cpp file that included the .h file?
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

  8. #8
    Confused Magos's Avatar
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    The definition must go into a source file
    It should go into a source file, but it doesn't have to. It can be defined inline in the header (has some uses though not many).
    MagosX.com

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  9. #9
    ATH0 quzah's Avatar
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    Code:
    Someclass::Someclass()
    {
        ~Someclass();
    }

    Quzah.
    Hope is the first step on the road to disappointment.

  10. #10
    Politics&Cpp geek Da-Nuka's Avatar
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    still doesent work..
    While THIS works:

    Code:
    class SomeClass {
    public:
    ~SomeClass () {
    //and here I go, as long as i make EVERYTHING within the declaration
    }
    
    
    };
    Atleast, then the compiler shuts up and let me compile...
    But im a man of principles, and this is a ugly and uncorrect way to do it! d:

  11. #11
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    What lines does the error message point at? It says "first defined here", where is here?

    Make sure you don't have
    Code:
    ~SomeClass() { }
    instead of
    Code:
    ~SomeClass();
    as the declaration.

  12. #12
    Anal comment spacer DominicTrix's Avatar
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    Also, though I dont think this is what you have, in your implementation make sure you dont have:

    Code:
    ~SomeClass(); { }
    The semicolon would make it appear as another definition.
    "The most important thing about acting is honesty. If you can fake that you've got it made" - George Burns

  13. #13
    Work in Progress..... Jaken Veina's Avatar
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    Umm....I use Dev-C++ as well, and the code you posted in your very first post compiles and runs fine for me. Your book was correct. Your error is somewhere else. If you get a multiple definition error, then that's just what it is. You've probably #included the .h file more than once, therefore, it is defined/declared more than once. Here's what I have.

    main.cpp
    Code:
    #include <cstdlib>
    #include <iostream>
    
    using namespace std;
    
    #include "class.h"
    
    int main(int argc, char *argv[])
     {
      system("PAUSE");
      return EXIT_SUCCESS;
     }
    class.h
    Code:
    class SomeClass
     {
      public:
        ~SomeClass();  // Destructor declaration
     };
    
    SomeClass::~SomeClass()
     {
    
     }
    Last edited by Jaken Veina; 06-14-2005 at 01:10 PM.

  14. #14
    Politics&Cpp geek Da-Nuka's Avatar
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    ... I manually deleted all makefiles, objectfiles and various project-builds, restarted my computer, and clicked "rebuild all", and it finaly worked !

  15. #15
    Work in Progress..... Jaken Veina's Avatar
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    Heh. Dev-C++ is wierd, At least you got it working.

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