C to C++ migration for typedef struct

This is a discussion on C to C++ migration for typedef struct within the C++ Programming forums, part of the General Programming Boards category; I have the following code that define the camera control feature in *.h . The code was written in C. ...

  1. #1
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    Cool C to C++ migration for typedef struct

    I have the following code that define the camera control feature in *.h . The code was written in C. However for my project, I use C++ (VS C++ 2005). The problem is when I force the VS to use C compiler, this code works fine. But when I use C++ compiler, I have the error from PCAM_FEATURE_CONTROL_STRUCT.

    Code:
    // Camera control feature structure
    typedef struct 
    {
        int   SliderID;
        int   AutoCheckID;
        int   OnePushButtonID;
        int   MinValueID;
        int   MaxValueID;
        int   CurrentValueID;
        int   InqOID;
        int   ControlOID;    void    (*ControlOnAuto)(PCAM_FEATURE_CONTROL_STRUCT , HWND , PFIREi_CAMERA_FEATURE_CONTROL_REGISTER);
        void    (*ControlOnOnePush)(PCAM_FEATURE_CONTROL_STRUCT , HWND , PFIREi_CAMERA_FEATURE_CONTROL_REGISTER);
    } CAM_FEATURE_CONTROL_STRUCT, *PCAM_FEATURE_CONTROL_STRUCT;
    the compile error message is
    Code:
    c:\controler.h(82) : error C2061: syntax error : identifier 
    'PCAM_FEATURE_CONTROL_STRUCT'
    It seems that the problem is about forward reference. Since PCAM_FEATURE_CONTROL_STRUCT is used before it is defined later.

    How can I modify this structure to work with C++ compiler? Thanks

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
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    You don't need to typecast structs in C++.
    Code:
    struct CAM_FEATURE_CONTROL_STRUCT
    {
        int   SliderID;
        int   AutoCheckID;
        int   OnePushButtonID;
        int   MinValueID;
        int   MaxValueID;
        int   CurrentValueID;
        int   InqOID;
        int   ControlOID;
        void    (*ControlOnAuto)(PCAM_FEATURE_CONTROL_STRUCT , HWND , PFIREi_CAMERA_FEATURE_CONTROL_REGISTER);
        void    (*ControlOnOnePush)(PCAM_FEATURE_CONTROL_STRUCT , HWND , PFIREi_CAMERA_FEATURE_CONTROL_REGISTER);
    };
    Is fine.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  3. #3
    Registered User hk_mp5kpdw's Avatar
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    Quote Originally Posted by alexy01 View Post
    It seems that the problem is about forward reference. Since PCAM_FEATURE_CONTROL_STRUCT is used before it is defined later.

    How can I modify this structure to work with C++ compiler? Thanks

    Where is it 'defined later' and can that definition be moved ahead prior to this struct's declaration (or a forward declaration)?

    [edit]Nevermind, didn't see the second part of the initial typedef.[/edit]
    Last edited by hk_mp5kpdw; 02-12-2008 at 11:53 AM.
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
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  4. #4
    Cat without Hat CornedBee's Avatar
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    I don't think the code is even valid ISO C, even if the compiler accepts it. Anyway, Elysia's way ought to work.
    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."
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  5. #5
    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by CornedBee View Post
    I don't think the code is even valid ISO C, even if the compiler accepts it.
    I think I missed that part. But this was discussed before, wasn't it? If a struct refers to itself, it must first have an actual name, so you access it through its name and not the typedef.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  6. #6
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    If a struct refers to itself, it must first have an actual name, so you access it through its name and not the typedef.
    Thanks Elysia.
    Could you point me to the thread that we have the discussion on this topic? ( I am very new here)
    Or can you show me the brief example how to write it? Thanks man.

  7. #7
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by alexy01 View Post
    How can I modify this structure to work with C++ compiler? Thanks
    Like this:

    Code:
    // Camera control feature structure
    typedef struct CAM_FEATURE_CONTROL_STRUCT
    {
        int   SliderID;
        int   AutoCheckID;
        int   OnePushButtonID;
        int   MinValueID;
        int   MaxValueID;
        int   CurrentValueID;
        int   InqOID;
        int   ControlOID;    void    (*ControlOnAuto)(CAM_FEATURE_CONTROL_STRUCT *, HWND , PFIREi_CAMERA_FEATURE_CONTROL_REGISTER);
        void    (*ControlOnOnePush)(CAM_FEATURE_CONTROL_STRUCT *, HWND , PFIREi_CAMERA_FEATURE_CONTROL_REGISTER);
    } *PCAM_FEATURE_CONTROL_STRUCT;
    Changed areas in red. If your goal is simply to get it to compile, that is probably enough.

    However, the callback members of this struct should be hinting to you to create a CAM_FEATURE_CONTROL_STRUCT base class with virtual functions ControlOnAuto() and ControlOnOnePush(), and to derive from this to produce concrete instances implementing this interface. C-style callbacks are not a good thing in C++.

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