Function returning pointer to function

This is a discussion on Function returning pointer to function within the C++ Programming forums, part of the General Programming Boards category; Hello, I am getting a compilation error for this: Code: int(*)(int)fun(); What I am trying to declare is a function ...

  1. #1
    DL1
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    Function returning pointer to function

    Hello,

    I am getting a compilation error for this:

    Code:
    int(*)(int)fun();
    What I am trying to declare is a function that returns a pointer to a function taking an int argument and returning an int. Can anybody tell me where the problem is? Thanks.

  2. #2
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by DL1
    What I am trying to declare is a function that returns a pointer to a function taking an int argument and returning an int. Can anybody tell me where the problem is?
    When I get confused, I just "cheat" with a typedef:
    Code:
    typedef int (*Function)(int);
    
    Function fun();
    It makes the code more readable, anyway.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    It is easiest if you use a typedef:
    Code:
    typedef int (*fn)(int); // typedef fn as a function that takes an int and returns an int
    
    fn fun(); // Declare fun() which returns a function that takes an int and returns an int
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    DL1
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    Thanks. That's what I ended up doing. I am still puzzled as to why my initial declaration didn't work though. I can't see any difference between it and the typedef version, other than that the latter introduces a new name.

  5. #5
    and the Hat of Guessing tabstop's Avatar
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    So far as I can tell, the real version is this:
    Code:
    int (*(fun(void))) (int);
    What you originally posted is ... well, I'm pretty sure it's not even a little bit syntactically valid.

  6. #6
    DL1
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    Nicely put. I see now where I went wrong, I think.

    And if the function took an argument of the same pointer type, it would presumably be declared as follows:

    Code:
    int (*(fun(int(*)(int)))) (int);
    Last edited by DL1; 08-07-2009 at 10:52 AM.

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    That's correct.
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