typedef question.

This is a discussion on typedef question. within the C++ Programming forums, part of the General Programming Boards category; I've read that you can use typedef to create a alias of a datatype, as example: typedef long miles; // ...

  1. #1
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    typedef question.

    I've read that you can use typedef to create a alias of a datatype, as example:
    typedef long miles; // define miles as an alias for long

    but then I saw this code:

    typedef QWidget * (*createModule_t)(QWidget *, const char *, const QXmlAttributes *);
    typedef void (*destroyModule_t)(QWidget *);

    what happens in these 2 lines?
    (QXmlAttributes and QWidget are classes)
    Last edited by mikalv; 06-23-2008 at 04:40 PM.

  2. #2

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    The syntax for declaring typedefs is just like initializing objects.

    Code:
    // Pointer to function returning int:
    int (*ptr)();
    
    // Alias of 'pointer to a function returning int':
    typedef int(*ptr_t)();
    So in your example, createModule_t is a datatype equivalent to a pointer to a function taking 3 parameters and returning a QWidget*.

    destoryModule_t is a datatype equivalent to a pointer to a function taking a QWidget* and returning void.

  3. #3
    Unregistered User Yarin's Avatar
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    WNDPROC and THREAD_ENTRY_POINT are some good examples of this.
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

  4. #4
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    so that's means that it's a way to make custom datatypes?

  5. #5
    C++ Witch laserlight's Avatar
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    Somewhat, though it is more like a way to give new names to existing types.
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