References¶

Pointers, Seen Differently: References (1)¶

Problem

Passing parameters by copy is expensive
Especially when objects are large (well, a point is not so large, but you get the point)

class point
{
public:
    float distance(point p) const
    {
        int dx = abs(_x-p._x);
        int dy = abs(_y-p._y);
        return sqrt(dx*dx+dy*dy);
    }
};

Problem
- Parameter is a copy
Solution
- Pass by pointer
- Even better: const pointer

Pointers, Seen Differently: References (2)¶

Definition

Usage

class point
{
public:
    float distance(const point *p) const
    {
        int dx = abs(_x-p->_x);
        int dy = abs(_y-p->_y);
        return sqrt(dx*dx+dy*dy);
    }
};

point a(1,2);
point b(2, 3);
float dist = a.distance(&b);

Problem

User has to take the address
Pointers can easily be NULL

Solution

References

Pointers, Seen Differently: References (3)¶

Definition

Usage

class point
{
public:
    float distance(const point &p) const
    {
        int dx = abs(_x-p._x);
        int dy = abs(_y-p._y);
        return sqrt(dx*dx+dy*dy);
    }
};

point a(1,2);
point b(2, 3);
float dist = a.distance(b);

Pretty, because …

Looks like ordinary parameter passing
Compiler takes the address ⟶ physically, a pointer is passed
NULL pointer passing (nearly) impossible