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Re: I'm not able to find the error

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On 2019-12-04 17:54, alexo wrote:
> Hello guys,
> I've written this code to get acquainted to assignment operators,
> move constructors and move assignment operators, but I got a
> strange behavior in my code:
> I report it in its fullness because it's 123 lines:
> 
> // code starts here
> #include <iostream>
> 
> using std::cout;
> using std::ostream;
> 
> class Vector
> {
>      friend ostream& operator<<(ostream& os, Vector& v)
>      {
>          for(size_t i=0; i<v.size(); i++)
>              os << v[i] << ' ';
> 
>          return os << '\n';
>      }
> 
>      public:
>      Vector(int n=5) : sz(n), data( new int[n])
>      {
>          for(size_t i=0; i < sz; i++)
>          data[i] = 0;
>      }
> 
>      Vector(const Vector& r) :              // the copy constructor
>          sz(r.size()),
>          data( new int[sz] )
>      {
>          for(size_t i=0; i < sz; i++)
>              data[i] = r.data[i];
>      }
> 
> 
>      Vector(const Vector&& r)               // the move constructor
>              sz{r.size()},
>              data{r.data}
>      { }
> 
>      Vector& operator= (const Vector& r)    // the copy assignment
>      {
>          delete [] data;
> 
>          sz = r.size();
>          data = new int[sz];
> 
>          for(size_t i=0; i < sz; i++)
>              data[i] =  r.data[i];
> 
>          return *this;
>      }
> 
>      Vector& operator= (const Vector&& r)    // the move assignment
>      {
>          delete [] data;
> 
>          data = new int[r.size()];
>          data = r.data;
> 
>          return *this;
>      }
> 
>      ~Vector()                                 // the destructor
>      {
>          cout << "deleting memory of array ";
>          cout << *this;
> 
>          delete [] data;
>          data = nullptr;
>      }
> 
>      unsigned int size() const { return sz; }
> 
>      int& operator[] (int i) { return data[i]; }
> 
>      Vector operator+(Vector& rhs)
>      {
>          size_t maxdim = sz, mindim = sz;
> 
>          if(sz < rhs.size())
>          {
>              maxdim = rhs.size();
>          }
>          else
>          {
>              mindim = rhs.size();
>          }
> 
>          Vector temp (maxdim);
> 
>          for(size_t i=0; i < mindim; i++)
>              temp[i] = data[i] + rhs[i];
> 
>          return temp;
>      }
> 
>      private:
>      size_t  sz;
>      int    *data;
> };
> 
> int main()
> {
>      Vector v1(3), v2;
> 
>      cout << "v1.size() = " << v1.size() << '\n'
>           << "v2.size() = " << v2.size() << "\n\n";
> 
>      v1[1] = 1; v2[2] = 3;   // using the index of '[]' operator
> 
>      cout << "v1 = " << v1;
>      cout << "v2 = " << v2;
> 
> 
>      Vector s;
>      s = v1 + v2;         // these two lines give runtime error
> 
> //    Vector s = v1 + v2;     // this line is ok instead
> 
>      cout << "v1 + v2 = " << s << '\n';
> 
>      cout << "destroying objects..." << '\n';
> 
>      return 0;
> }
> // code ends here
> 
> 
> Now I give a description of the error.
> g++ executing this code on my gives:
> 
> v1.size() = 3
> v2.size() = 5
> 
> v1 = 0 1 0
> v2 = 0 0 3 0 0
> deleting memory of array 0 1 3 0 0
> v1 + v2 = 0 0 -1704935408 22058 0
> 
> destroying objects...
> deleting memory of array 0 0 -1704935408 22058 0
> free(): double free detected in tcache 2
> aborted
> 
> As the title of the message says, I'm stuck.
> I did my best to write it, but evidently some subtle error lays
> between those lines.
> 
> If you comment the following:
> 
>      Vector s;
>      s = v1 + v2;
> 
> and uncomment
> 
> //    Vector s = v1 + v2;
> 
> the program behaves correctly.
> What could it be the problem?
> 
> Thank you.

Hi

      Vector(Vector&& r) // no const
              sz{r.size()},
              data{r.data}
      {
          r.data = nullptr; // you move from it, so r is empty
          r.sz   = 0;
      }

Same in operator=(Vector&& r)

data{std::move(r.data)} would not help because it is a simple pointer.

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I'm not able to find the error alexo <alelvb@inwind.it> - 2019-12-04 17:54 +0100
  Re: I'm not able to find the error Volker Wippel <Volker.Wippel@v2c2RemoveNoSpam.at> - 2019-12-04 18:40 +0100
  Re: I'm not able to find the error Daniel <danielaparker@gmail.com> - 2019-12-04 10:01 -0800
    Re: I'm not able to find the error Daniel <danielaparker@gmail.com> - 2019-12-04 10:06 -0800
  Re: I'm not able to find the error Manfred <noname@add.invalid> - 2019-12-04 20:16 +0100
    Re: I'm not able to find the error Manfred <invalid@add.invalid> - 2019-12-05 01:42 +0100
      Re: I'm not able to find the error alexo <alelvb@inwind.it> - 2019-12-05 03:45 +0100
        Re: I'm not able to find the error alexo <alelvb@inwind.it> - 2019-12-05 03:58 +0100
          Re: I'm not able to find the error Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2019-12-05 04:10 +0000
            Re: I'm not able to find the error alexo <alelvb@inwind.it> - 2019-12-05 05:45 +0100
          Re: I'm not able to find the error Manfred <noname@add.invalid> - 2019-12-05 17:29 +0100
  Re: I'm not able to find the error alexo <alelvb@inwind.it> - 2019-12-04 22:52 +0100
    Re: I'm not able to find the error Daniel <danielaparker@gmail.com> - 2019-12-04 16:47 -0800
      Re: I'm not able to find the error alexo <alelvb@inwind.it> - 2019-12-05 03:37 +0100

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