C++ for Scientists - Technische Universität Dresden

80 CHAPTER 3. CLASSES
One could not even write a loop over all elements.
To enable such iteration, we need a function like:
class vector
{
public:
double at(int i)
{
assert(i >= 0 && i < my size);
return data[i];
}
};
Summing the entries of vector v reads:
double sum= 0.0;
for (int i= 0; i < v.size(); i++)
sum+= v.at(i);
C ++ and C access entries of (fixed-size) arrays with the subscript operator. It is, thus, only
natural doing the same for (dynamically sized) vectors. Then we could rewrite the previous
example as:
double sum= 0.0;
for (int i= 0; i < v.size(); i++)
sum+= v[i];
This is more concise and shows more clearly what we are doing.
The operator overloading has the same syntax as the assignment operator and the implementation
from function at:
class vector
{
public:
double& operator[](int i)
{
assert(i >= 0 && i < my size);
return data[i];
}
};
With this operator we can access vector elements with brackets but only if the vector is mutable
vectors.
3.7.3 Constant member functions
This raises the more general question: How can we write operators and member functions that
accept constant objects? In fact, operators are a special form of member functions and can be
called like a member function:
v[i]; // is syntactic sugar for:
v.operator[](i);