Callback functions

This is a discussion on Callback functions within the C++ Programming forums, part of the General Programming Boards category; Okay, probably more of a generic c topic but am writing the program in c++. What I am wanting to ...

  1. #1
    Registered User
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    Callback functions

    Okay, probably more of a generic c topic but am writing the program in c++.

    What I am wanting to know is how would I go about writing a callback function.

    The term 'callback function' I am using to describe the process through which function A has the name of function B passed to it and will then call function B.

    As I am going to be passing it the name of a function that resides within a c++ class, are there any particular circumstances that need to be adhered to?
    WebmasterMattD
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  2. #2
    Registered User Codeplug's Avatar
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    Code:
    #include <iostream>
    using namespace std;
    
    int foo(long l)
    {
        cout << "foo(" << l << ")" << endl;
        return 0;
    }//foo
    
    int bar(long l)
    {
        cout << "bar(" << l << ")" << endl;
        return 1;
    }//bar
    
    // create a typename for a pointer to a function 
    // that returns int takes one long parameter
    typedef int (*foobar_ptr_t)(long);
    
    int main()
    {
        foobar_ptr_t fp1, fp2;
    
        fp1 = foo;
    
        // address-of operator (&) is ok too
        fp2 = &bar;
    
        fp1(1);
        fp2(2);
    
        return 0;
    }//main
    gg

  3. #3
    mustang benny bennyandthejets's Avatar
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    You may have to make the member function static. I believe it is not possible to pass a non-static member function pointer to a callback function. On the topic of function pointers, here is a good site.

    You probably don't want to pass a string for the function, to be used with GetProcAddress32(). Function pointers are much better suited for this purpose.

    What does the program actually do?
    benforbes@optusnet.com.au
    Microsoft Visual Studio .NET 2003 Enterprise Architect
    Windows XP Pro

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  4. #4
    Registered User Codeplug's Avatar
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    You can apply the above code using class methods as long as they are declared static.
    If you want the use "pointer to non-static member function" semantics, then read this.

    gg

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