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runtime error

Discussion in 'C++' started by aortizb, Sep 1, 2009.

  1. aortizb

    aortizb New Member

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    Can somebody tell me why this code does not work and how to fix it? It compiles but runtime errors appear:

    Code:
    #include <iostream>
    #include <vector>
    using namespace std;  
    
    template <class T>
    class Vec
    {
    public:
      // constructors
      Vec(int length); 
      Vec(int length, T typeValue); 
      Vec(const Vec<T>& rhsObj); 
      const Vec<T>& operator=(const Vec<T>& rhsObj);
      const Vec<T>& operator=(T& typeValue);
      const Vec<T>& operator*=(T typeVal);
      const Vec<T> operator*(T typeVal) const;
      const T& operator()(int index) const;
      T& operator()(int index);
      int getSize() const;
      ~Vec();
    private:
      vector<T> myVec_;
    };
    
    
    template<class T> 
    Vec<T>::
    Vec(int length)
    {
      myVec_ = vector<T>(length);
    }
    
    template<class T> 
    Vec<T>::
    Vec(int length, T typeValue)
    {
      myVec_ = vector<T>(length,typeValue);
    }
    
    template<class T> 
    Vec<T>::
    Vec(const Vec<T>& rhsObj) 
    {
      vector<T> myVec_(rhsObj.myVec_);
    }
    
    template<class T> 
    const Vec<T>& 
    Vec<T>::
    operator=(const Vec<T>& rhsObj)
    {
      myVec_ = rhsObj.myVec_;
      return *this;
    }
    
    template<class T> 
    const Vec<T>& 
    Vec<T>::
    operator=(T& typeValue)
    {
      for (unsigned i = 0; i < myVec_.size(); i++)
        (*this)(i) = typeValue;
      return *this;
    }
    
    template<class T>
    const Vec<T>&
    Vec<T>::
    operator*=(T typeVal)
    {  
      for (unsigned i = 0; i < myVec_.size(); i++)
      {
        (*this)(i) *= typeVal; 
      }
      return *this;
    } 
    
    template<class T>
    const Vec<T>
    Vec<T>::
    operator*(T typeVal) const
    {
      return (Vec<T>(*this) *= typeVal);
    } 
    
    template<class T>
    const T&
    Vec<T>::
    operator()(int index) const
    {
      return myVec_[index];
    } 
    
    template<class T>
    T&
    Vec<T>::
    operator()(int index)
    {
      return myVec_[index];
    } 
    
    template<class T> 
    int
    Vec<T>::
    getSize() const
    {
      return (myVec_.size());
    }
    
    template<class T> 
    Vec<T>::
    ~Vec()
    {
    }
    
    
    // ******************************************************************************
    // overloading externally since the first argument is not an object: typeVal*obj1
    // ******************************************************************************
    template<class T>
    const Vec<T>
    operator*(const T typeVal, const Vec<T>& obj1)
    {
      return (obj1*typeVal);
    }
    
    
    int main()
    {
      Vec<double> x(3,4);
      Vec<double> d = x*2.0;
      cout << d(0) << " " << d(1) << " " << d(2) << endl;
      return 0;
    }
    
     
  2. xpi0t0s

    xpi0t0s Mentor

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    What's it meant to do?
    What output do you expect from this code? (In particular, why do you expect THREE values, and what are they?)
    What are the errors?
     
  3. aortizb

    aortizb New Member

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    the code above is just a portion of another code that does some operations with vectors. At the beggining I created it as a child of std::vector, but i read that this is not a good idea, so i decided to do a wrapper of std::vector. The ouput to identify the error is just what i have in main(). The error is becuase "d" is not being compute, so d(0), d(1) and d(2). The problem is fixed when i remove the copy constructor, so the problem is there. I don't see why it is wrong? can anyone tell me how to rewrite the copy constructor? in principle, i don't need it since the default created by the compiler will be ok. But for generality i would like to know how to do it.

    thanks.
     
  4. xpi0t0s

    xpi0t0s Mentor

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    Are you sure the copy constructor is being invoked? For example have you tried putting a printf or a cout into it?
    TYPE var=<expr>; can sometimes invoke the copy constructor or operator=(), hence the question.
     
  5. aortizb

    aortizb New Member

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    Yes, I tried. It is being invoked.
     
  6. aortizb

    aortizb New Member

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    The correct constructor is:
    Code:
    template<class T> 
    Vec<T>::
    Vec(const Vec<T>& rhsObj) 
    {
      myVec_ = rhsObj.myVec_;
    }
    
    or
    Code:
    template<class T> 
    Vec<T>::
    Vec(const Vec<T>& rhsObj) :  myVec_ (rhsObj.myVec_)
    {
    }
    
    with this the code above is fixed.
    Also, is there any way I can do the following in the main() function:
    Code:
     int main()
    {
      Vec<double> x(3,4);
      Vec<double> d = 2*x;
      cout << d(0) << " " << d(1) << " " << d(2) << endl;
      return 0;
    } 
    
    without incurring in a compilation error because of 2 can be interpreted as more than one type? I mean I would like this to compile independently if I use 2*x or 2.0*x
     
  7. xpi0t0s

    xpi0t0s Mentor

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    I still don't see what numbers you're expecting this to output. I can guess that d(0) will be 6 and d(1) will be 8, but what do you think d(2) will be?
     
  8. xpi0t0s

    xpi0t0s Mentor

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    For 2*x to work you need operator*(int,Vec).
     
  9. aortizb

    aortizb New Member

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    No, d(0)=d(1)=d(2) = 8. There is an easy way to solve all posibilities no matter if it is integer or double. I found it today in the morning:

    Code:
    template<class T, class U>
    const Vec<T>
    operator*(const U typeVal, const Vec<T>& obj1)
    {
      return (obj1*typeVal);
    }
    
     

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