3. argument type checkinng in Constructor

argument type checkinng in Constructor

  • N

    Yes I did get a warning. But it is not enough. I want it to be error in the compile process. Do you know how?

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  • J

    add a declaration of an overload:

    Ration(double n, double d);

    but don't implement it.
    When the Compiler selects this constructor as the most fitting one you'll get a linker error because it's not implemented. For a compile-time error you might consider making it private.

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  • N

    Thanks for your answer. Still not working. It looks like a simple problem but I try so many approaches already.

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  • 7

    Try this:
    explicit Rational( int n, int d);

    This will forbid implicit typecasts resulting in a compile time error when you try to pass other types than int.

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  • J

    no it doesn't.

    It prevents automatic conversion which isn't possible anyway with two arguments.

    notkit:
    what doesn't work?
    Could you show an example?

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  • N

    Look interesting. I try it as you suggested but the constructor Rational(int n, int d) is still called when I call Rational(3.0, 4.0). The "3.0" and "4.0" are converted into integer and only warning are given.

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  • J

    try this:

    class Rational
{
public:
  Rational(int n, int d) { // your Code here }
private:
  Rational(double n, double d); // no implmentation
};

int main()
{
  Rational(2,3); // should work fine
  Rational(2.0,3.0); // should result in a compilation error
}
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  • N

    Here you are. Class Rational is to represent rational number (e.g. 3/4) and normally a double should not be able to expressed as rational number. 😉

    // this is the header file
    class Rational
    {
    public:
    // Constructor
    Rational(int n = 0, int d = 1) // denomiator alway more than zero
    {
    if (d != 0) {
    m_num = n;
    m_den = d;
    if(m_den != 1)
    Normalize();
    }
    }

    // operators
    Rational &operator =(int i);

    operator double() { return (double)m_num/(double)m_den; }
    Rational operator +() { return Rational(m_num, m_den); }
    Rational operator -() { return Rational(-m_num, m_den); }

    Rational operator +(const Rational &src);
    double operator +(const double d);
    Rational operator -(const Rational &src);
    double operator -(const double d);
    Rational operator *(const Rational &src);
    double operator *(const double d);
    Rational operator /(const Rational &src);
    double operator /(const double d);

    // Print out the contents of the instance
    void Print(); // Implemented in the rational.cpp file

    // Access member functions
    int Numerator() { return m_num; }
    int Denominator() { return m_den; }

    private:
    // Private functions
    void Normalize(); // To be implemented in the rational.cpp file

    // Private data
    int m_num; // numerator
    int m_den; // denominator
    };

    //
    int main()
    {
    a = 1.0; // Should not compile
    a = Rational(3.0, 3.0); // Should not compile

    return 0;
    }

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  • N

    This is the implementation for Rational class.

    #include <iostream.h>
    #include "rational.h"

    void Rational::Normalize()
    {
    if (m_den<0) {
    m_num = -m_num;
    m_den = -m_den;
    } else {
    m_num = m_num;
    m_den = m_den;
    }

    if (m_num == 0) {
    return;
    }

    // Euclid's algorithm...
    int a, b, r;

    if (m_num > 0 && m_num > m_den) {
    a = m_num;
    b = m_den;
    } else if (m_num > 0){
    a = m_den;
    b = m_num;
    } else if (-m_num > m_den) {
    a = -m_num;
    b = m_den;
    } else {
    a = m_den;
    b = -m_num;
    }

    r = 1;
    while (r > 0)
    {
    r = a % b;
    a = b;
    b = r;
    }

    // record the normalized value to m_num and m_den
    m_num = m_num/a;
    m_den = m_den/a;

    return;

    }

    void Rational::Print()
    {
    cout << "(" << m_num << "/" << m_den << ")";
    }

    Rational &Rational::operator =(int i)
    {
    m_num = i;
    m_den = 0;
    return *this;
    }

    Rational Rational::operator +(const Rational &src)
    {
    return( Rational( m_num*src.m_den + src.m_num*m_den, m_den*src.m_den ) );
    }

    double Rational::operator +(const double d)
    {
    return( double(m_num)/double(m_den) + d );
    }

    Rational Rational::operator -(const Rational &src)
    {
    return( Rational( m_num*src.m_den - src.m_num*m_den, m_den*src.m_den ) );
    }

    double Rational::operator -(const double d)
    {
    return( double(m_num)/double(m_den) - d );
    }

    Rational Rational::operator *(const Rational &src)
    {
    return( Rational( m_num*src.m_num, m_den*src.m_den ) );
    }

    double Rational::operator *(const double d)
    {
    return( double(m_num)/double(m_den) * d );
    }

    Rational Rational::operator /(const Rational &src)
    {
    return( Rational( m_num*src.m_den, m_den*src.m_num ) );
    }

    double Rational::operator /(const double d)
    {
    return( double(m_num)/double(m_den) / d );
    }

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  • F

    Beats me where you left Jester's suggestion. Already disposed of it? 😃
    You should honestly give it a try; public for linker-, private for compiler-error.

    NB:

    Rational &Rational::operator =(int i)
{
  m_num = i;
  // m_den = 0; // this ain't exactly what you want, is it? how 'bout that:
  m_den = 1;
  return *this;
}

// moreover,
if (m_den<0) {
  m_num = -m_num;
  m_den = -m_den;
}
// else branches aren't mandatory  ;) 
/*
  else {
  m_num = m_num;
  m_den = m_den;
} 
*/
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  • N

    to Jester,

    cool. The Rational(3.0, 4.0) does not compile now. But the

    Rational a;
    a = 3.0; // Ratinal = double should not compile

    still compiles. And this should not because double should not be expressed as Rational numbers.

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  • ?

    use the same technique for operator=

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  • N

    Oh finally. Problem solved. I was like trying to solve this easy-looking problems for days. Danke Sehr! Danke schon! Danke Danke! Ho! 😉

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