Re: operator[][][]

From: (Frederick Gotham)
Thu, 27 Jul 2006 18:24:51 GMT
Carl Barron posted:

template <class T,size_t cols,size_t rows>
class Matrix
   T data[rows*cols];
   struct subscript_proxy
      T *data;
      int i;
      subscript_proxy(T *a,int b):data(a),i(b){}
      T & operator [] (int j) {return data[i+j];}
   subscript_proxy operator [] (int i)
      return subscript_proxy(data,i*cols);
or build an array of T*s in the ctor

template<class T,size_t rows,size_t cols>
class Matrix
   T data[rows*cols];
   T *row_start[rows];
      T *p = data;
      for(int i=0;i!=rows;++i,p+=cols)
         row_start[i] = p;
   T * operator [] (int i) {return row_start[i];}

now Matrix A;
      x = A[i][j] first calls Matrix::operator [](i) and then the
operator [](j) [either the built in for double * , or
subscript_proxy::operator [] depending on which of above
implementations is used ]

Yes, I'm well aware of that method. (A recent post of mine: )

Code would be a lot nicer (and would perform a lot better) if we could
simply define:

    T &operator[][][](unsigned,unsigned,unsigned);


Frederick Gotham

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