confused: static method const???

This is a discussion on confused: static method const??? within the C++ Programming forums, part of the General Programming Boards category; I'm working on this program and is such a slow progress, I keep stumbling on so small things... Like this ...

  1. #1
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    Unhappy confused: static method const???

    I'm working on this program and is such a slow progress, I keep stumbling on so small things... Like this one. My textbook is showing a class with private static int, and a public static method which is also const as it just displays the private member... I declared my own class, following the guidelines from the textbook and when I compile it (DevC++ 4.9.9.2) it tells me 34 C:\Dev-Cpp\inheritance_project\main.cpp static member function `static int MyString::numStrings()' cannot have `const' method qualifier
    Why is that?
    I wrote it as such:
    Code:
    private:
    static int counter;
    public:
    static int numStrings(void)  const { return counter; }
    What's wrong then???

  2. #2
    Guest Sebastiani's Avatar
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    const in that context implies that the object calling it will not be modified, but since static functions are not called with an object, there's no logical reason to declare as such.
    Code:
    #include <cmath>
    #include <complex>
    bool euler_flip(bool value)
    {
        return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) 
            * std::complex<float>(std::atan(1.0)
            *(1 << (value + 2)))
        ).real() < 0;
    }

  3. #3
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    OK... that sounds reasonable. Does most of compliers give errors at this point? Or is it only Dev?

  4. #4
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    Dev-CPP is not a compiler. It's merely an IDE, using the MinGW port, of the GNU GCC compiler. GCC is pretty standards compliant and widely used, meaning: you might as well try fix your code, not the compiler.

  5. #5
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    Quote Originally Posted by kocika73
    OK... that sounds reasonable. Does most of compliers give errors at this point? Or is it only Dev?
    as jaket said, devcpp is an IDE not a compiler.

    C++ compilers are required to complain (or, at least, fail to compile) when they encounter a static const function.

  6. #6
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    So the book is wrong then.

  7. #7
    C++ Witch laserlight's Avatar
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    Out of curiosity, what book might that be?
    C + C++ Compiler: MinGW port of GCC
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    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  8. #8
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    Quote Originally Posted by kocika73
    So the book is wrong then.
    If "the book" claims a static const member function is valid C++ then, yes, it is wrong. If a code example in the book is of that form, then that example is wrong (which may mean the book is crap, or may just be an error in the particular example).

    Like laserlight, I'm curious about what book you're using.

  9. #9
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    It is Object-Oriented Programming in C++ by Johnsonbaugh and Kalin. Example 3.7.4 on p. 154 (the top of page. Later they modify that without explaining why they leave out the "const")

  10. #10
    #define WORLD "sad place" LinuxCoder's Avatar
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    If they later drop the const all points out that it is a typo. It's probably already corrected in later editions (if there are any) or on some online errata, otherwise you might wanna consider sending the author an e-mail with that info.

    Cheers

  11. #11
    Frequently Quite Prolix dwks's Avatar
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    Non-static member functions get passed a pointer to the object they are operating on, called this. All the function's access to its class is through this pointer. A function declared like this:
    Code:
    void func() const {}
    has its this pointer declared as
    Code:
    classname *const this
    which prevents the function from changing the class's data.

    Since static functions aren't passed a this pointer (that's what makes them static), you cannot declare a static function to be const.
    Code:
    static void constfunc() const {}  /* error */
    dwk

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