C++ for Scientists - Technische Universität Dresden

82 CHAPTER 3. CLASSES
class matrix
{
public:
matrix() : nrows(0), ncols(0), data(0) {}
matrix(int nrows, int ncols)
: nrows(nrows), ncols(ncols), data( new double[nrows ∗ ncols] ) {}
matrix(const matrix& that)
: nrows(that.nrows), ncols(that.ncols), data(new double[nrows ∗ ncols])
{
for (int i= 0, size= nrows∗ncols; i < size; ++i)
data[i]= that.data[i];
}
∼matrix() { if (data) delete [] data; }
void operator=(const matrix& that)
{
assert(nrows == that.nrows && ncols == that.ncols);
for (int i= 0, size= nrows∗ncols; i < size; ++i)
data[i]= that.data[i];
}
int num rows() const { return nrows; }
int num cols() const { return ncols; }
private:
int nrows, ncols;
double∗ data;
};
So far, the implementation is done in the same manner as before: variables are private, the
constructors establish defined values for all members, the copy constructor and the assignment
are consistent, size information are provided by a constant function.
What is still missing is the access to the matrix entries.
Be aware!
The bracket operator accepts only one argument.
That means we cannot define
double& operator[](int r, int c) { ... }
Approach 1: Parenthesis
The simplest way handling multiple indices is replacing the square brackets with parentheses:
double& operator()(int r, int c)