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Float that initializes to NaN

This is a discussion on Float that initializes to NaN within the C++ Programming forums, part of the General Programming Boards category; Hi! I want to make a class that works exactly like a float, only that it is initialized to NaN ...

  1. #1
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    Float that initializes to NaN

    Hi! I want to make a class that works exactly like a float, only that it is initialized to NaN when the default constructor is called and if DEBUG is defined so that I can easily detect when I have an uninitialized float. Is there some simple way to do this? Thanks in advance!
    Last edited by then; 05-16-2012 at 10:24 AM.

  2. #2
    Registered User manasij7479's Avatar
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    I'm not sure if this is portable.
    Code:
    #ifdef DEBUG
    float_var = std::sqrt(-1);
    #endif
    I assume you encapsulate a float variable.
    If, on the other hand, you want to implement floating point numbers by yourself.. it is *much* more complicated and I have no idea.

    [EDIT]
    I just found out that there is a NAN macro in math.h .
    So, "foo = NAN;" would be a better idea .
    Last edited by manasij7479; 05-16-2012 at 10:36 AM.
    Manasij Mukherjee | gcc-4.8.2 @Arch Linux
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    Thank you, that is one way to generate a NaN, yes. But the question was how to make the kind of class I described above.

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    Registered User manasij7479's Avatar
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    Quote Originally Posted by then View Post
    Thank you, that is one way to generate a NaN, yes. But the question was how to make the kind of class I described above.
    Just encapsulate a float variable and overload the operators.
    (And possibly throw some exceptions within them.)
    I don't think there is anything else to it.
    Last edited by manasij7479; 05-16-2012 at 10:40 AM.
    Manasij Mukherjee | gcc-4.8.2 @Arch Linux
    Slow and Steady wins the race... if and only if :
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    2.The fast and unsteady suddenly falls asleep while running !



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    I'm trying. So far I the class declaration looks like this:

    Code:
    template<typename T>
    class base_safe_float
    {
    public:
        /* Constructors */
        base_safe_float(); // Default constructor
        template<typename T2> base_safe_float<T>(T2 s); // Copy conversion constructor
    
        /* Conversion operator */
        operator T() const;
    
        /* Assignment operators */
        template<typename T2> base_safe_float<T>& operator =(const T2&);
        template<typename T2> base_safe_float<T>& operator+=(const T2&);
        template<typename T2> base_safe_float<T>& operator-=(const T2&);
        template<typename T2> base_safe_float<T>& operator*=(const T2&);
        template<typename T2> base_safe_float<T>& operator/=(const T2&);
    
    private:
        T v; /* Value */
    };
    I don't know if this is all constructors and operators I need to define. However, when I'm trying to use this, I'm getting errors like

    Code:
    error: operands to ?: have different types 'int' and 'ftype'
    (ftype is typedefd as base_safe_float<float>)

    It is complaining on the row

    Code:
    f = f < 0 ? 0 : f;
    where f is a variable of type ftype. How can I get rid of this error without modifying the line that's generating it (since the line shouldn't generate the error)?

    If the class is supposed to work exactly like a float (or as a double, depending on what the template argument is), I must find some way to get rid of all these compile errors.



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    don't forget about comparison (==, !=, <, >, <=, >=) operators

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    Quote Originally Posted by Elkvis View Post
    don't forget about comparison (==, !=, <, >, <=, >=) operators
    Doesn't the compiler realize that it can just use the conversion operator and then compare a float against whatever it is I want to compare it against?

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    I don't think you can make that assumption, not to mention implicit conversion operators, while legal in the code, are not recommended, as you may get unexpected results.

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    Algorithm Dissector iMalc's Avatar
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    I have the guts of a lightweight class that implements exactly enough to do this kind of thing already. I could have this made in about 10 minutes after work today. Might post back in about 10 hours with it.
    My homepage
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    Master Apprentice phantomotap's Avatar
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    How can I get rid of this error without modifying the line that's generating it (since the line shouldn't generate the error)?
    O_o

    It should generate the error.

    Both results of the conditional operator are required to be the same type or convertible to the same type. The compiler is not allowed to choose the conversion. If the conversion can be assumed because the types have an inheritance relationship the compiler will implicitly convert a child class reference to a parent class reference. If the relationship between types are not direct one or both types must be explicitly cast.

    You need to explicitly cast the zero (an integer value) to type `T'.

    I don't think you can make that assumption, not to mention implicit conversion operators, while legal in the code, are not recommended, as you may get unexpected results.
    There is no problem in this context. The type of conversion is directly related to the type held by the class. Without the conversion the class can't be used as a real `float' could be used even if every other operator is provided.

    However, the other operators should still be provided. You can catch an uninitialized value without them; with them you can catch other semantic errors later.

    Soma

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    Quote Originally Posted by phantomotap View Post
    O_o
    I don't get this error when f just is a normal float, that is why a base_safe_float<float> shouldn't generate any error here either.

    Quote Originally Posted by phantomotap View Post
    However, the other operators should still be provided. You can catch an uninitialized value without them; with them you can catch other semantic errors later.

    Soma
    Okay. I have already started to write the other operators but I deactivated them since I didn't think they would contribute anything to the class when I had the conversion operator. But there are really many operators, should I overload all of them?

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    Quote Originally Posted by iMalc View Post
    I have the guts of a lightweight class that implements exactly enough to do this kind of thing already. I could have this made in about 10 minutes after work today. Might post back in about 10 hours with it.
    It would be interesting to see your implementation and if it differs something from my class (except from that my isn't finished yet).

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    Quote Originally Posted by then View Post
    It would be interesting to see your implementation and if it differs something from my class (except from that my isn't finished yet).
    I would also like to see either/both of the implementations.

    Tim S.
    "Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the universe trying to produce bigger and better idiots. So far, the Universe is winning." Rick Cook

  14. #14
    Master Apprentice phantomotap's Avatar
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    I don't get this error when f just is a normal float, that is why a base_safe_float<float> shouldn't generate any error here either.
    Your opinion is irrelevant.

    You are simply wrong.

    Code:
    f < 0 ? 0 : f;
    In this code that you posted the both results differ beyond what the compiler is allowed to infer.

    The compiler can't simply choose because both are perfectly valid.

    Code:
        f < 0 ? static_cast<ftype>(0) : f;
    Code:
        f < 0 ? 0 : static_cast<float>(f);
    These are both equally valid so the compiler is not allowed to choose.

    Code:
    (condition) ? (true_result) : (false_result);
    You are still wrong if you are just trying to say "The compiler should convert the class instance because a conversion operator is available." The conversion operator isn't considered here because the isolated expression `false_result' assumes no specific type.

    Code:
    class OBase
    {
    };
    
    class ODerived1:
        public OBase
    {
    };
    
    class ODerived2:
        public OBase
    {
    };
    
    int main()
    {
        ODerived1 * lD1(0);
        ODerived2 * lD2(0);
        OBase * lB1(lD1);
        OBase * lB2(lD2);
        OBase * lB3((true) ? (lD1) : (lD2));
        return(0);
    }
    You are also wrong if you think the target variable type has anything to do with it. The type that the result of the condition operator expression may be assigned isn't considered by the compiler; the type of the expression must be fixed in isolation.

    The upshot to all of this is that you must be explicit with respect to the types involved in a conditional operator expression. If you don't want to do this for whatever reason, you can't use the conditional operator; you would need to use a normal branch.

    Soma

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    Quote Originally Posted by phantomotap View Post
    Your opinion is irrelevant.

    You are simply wrong.
    So you should have an opinion that is relevant but not me? And I don't know what it was I wrote that you think is wrong. It is easy to just ignore the rest of what you are writing when you start your post with two quite provoking/disparaging statements; you know that, right?

    Apparently my compiler could chose between the two cases (although I don't know how it did it) and that is actually what matters to me. If it behaves in one way for float it should behave in the same way for the class I'm creating. I don't know what is correct behavior and which is not (which you seems to know), but I don't want it to change it when I switch type.

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