Qt 4.0: QPoint Class Reference

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# QPoint Class Reference
[QtCore module]

The QPoint class defines a point in the plane. More...

    #include <QPoint>

- List of all members, including inherited members

### Public Functions

- QPoint ()
- QPoint ( int xpos, int ypos )
- bool isNull () const
- int manhattanLength () const
- int & rx ()
- int & ry ()
- void setX ( int x )
- void setY ( int y )
- int x () const
- int y () const
- QPoint & operator*= ( qreal c )
- QPoint & operator+= ( const QPoint & p )
- QPoint & operator-= ( const QPoint & p )
- QPoint & operator/= ( qreal c )

### Related Non-Members

- bool operator!= ( const QPoint & p1, const QPoint & p2 )
- const QPoint operator* ( const QPoint & p, qreal c )
- const QPoint operator* ( qreal c, const QPoint & p )
- const QPoint operator+ ( const QPoint & p1, const QPoint & p2 )
- const QPoint operator- ( const QPoint & p1, const QPoint & p2 )
- const QPoint operator- ( const QPoint & p )
- const QPoint operator/ ( const QPoint & p, qreal c )
- QDataStream & operator<< ( QDataStream & s, const QPoint & p )
- bool operator== ( const QPoint & p1, const QPoint & p2 )
- QDataStream & operator>> ( QDataStream & s, QPoint & p )

## Detailed Description

The QPoint class defines a point in the plane.

A point is specified by an x coordinate and a y coordinate. The coordinates are specified using integer numbers. QPointF provides points with floating point accuracy.

The coordinates are accessed by the functions x() and y(); they can be set by setX() and setY() or by the reference functions rx() and ry().

Given a point p, the following statements are all equivalent:

        p.setX(p.x() + 1);
        p += QPoint(1, 0);
        p.rx()++;

A QPoint can also be used as a vector. Addition and subtraction of QPoints are defined as for vectors (each component is added separately). You can divide or multiply a QPoint by an `int` or a `qreal`. The function manhattanLength() gives an inexpensive approximation of the length of the QPoint interpreted as a vector.

Example:

        //QPoint oldPos is defined somewhere else
        MyWidget::mouseMoveEvent(QMouseEvent *e)
        {
            QPoint vector = e->pos() - oldPos;
            if (vector.manhattanLength() > 3)
            ... //mouse has moved more than 3 pixels since oldPos
        }

QPoints can be compared for equality or inequality, and they can be written to and read from a QStream.

See also QPolygon, QSize, QRect, and QPointF.

## Member Function Documentation

### QPoint::QPoint ()

Constructs a point with coordinates (0, 0) (isNull() returns true).

### QPoint::QPoint ( int xpos, int ypos )

Constructs a point with x value xpos and y value ypos.

### bool QPoint::isNull () const

Returns true if both the x value and the y value are 0; otherwise returns false.

### int QPoint::manhattanLength () const

Returns the sum of the absolute values of x() and y(), traditionally known as the "Manhattan length" of the vector from the origin to the point. The tradition arises because such distances apply to travelers who can only travel on a rectangular grid, like the streets of Manhattan.

This is a useful, and quick to calculate, approximation to the true length: sqrt(pow(x(),2)+pow(y(),2)).

### int & QPoint::rx ()

Returns a reference to the x coordinate of the point.

Using a reference makes it possible to directly manipulate x.

Example:

        QPoint p(1, 2);
        p.rx()--;         // p becomes (0, 2)

See also ry() and setX().

### int & QPoint::ry ()

Returns a reference to the y coordinate of the point.

Using a reference makes it possible to directly manipulate y.

Example:

        QPoint p(1, 2);
        p.ry()++;         // p becomes (1, 3)

See also rx() and setY().

### void QPoint::setX ( int x )

Sets the x coordinate of the point to x.

See also x() and setY().

### void QPoint::setY ( int y )

Sets the y coordinate of the point to y.

See also y() and setX().

### int QPoint::x () const

Returns the x coordinate of the point.

See also setX() and y().

### int QPoint::y () const

Returns the y coordinate of the point.

See also setY() and x().

### QPoint & QPoint::operator*= ( qreal c )

Multiplies this point's x and y by c, and returns a reference to this point.

Example:

        QPoint p(-1, 4);
        p *= 2.5;          // p becomes (-3,10)

Note that the result is rounded to the nearest integer as points are held as integers.

See also QPointF.

### QPoint & QPoint::operator+= ( const QPoint & p )

Adds point p to this point and returns a reference to this point.

Example:

        QPoint p( 3, 7);
        QPoint q(-1, 4);
        p += q;            // p becomes (2,11)

### QPoint & QPoint::operator-= ( const QPoint & p )

Subtracts point p from this point and returns a reference to this point.

Example:

        QPoint p( 3, 7);
        QPoint q(-1, 4);
        p -= q;            // p becomes (4,3)

### QPoint & QPoint::operator/= ( qreal c )

Divides both x and y by c, and returns a reference to this point.

Example:

        QPoint p(-3, 10);
        p /= 2.5;           // p becomes (-1,4)

Note that the result is rounded to the nearest integer as points are held as integers.

See also QPointF.

## Related Non-Members

### bool operator!= ( const QPoint & p1, const QPoint & p2 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns true if p1 and p2 are not equal; otherwise returns false.

### const QPoint operator* ( const QPoint & p, qreal c )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns the QPoint formed by multiplying both components of p by c.

Note that the result is rounded to the nearest integer as points are held as integers.

See also QPointF.

### const QPoint operator* ( qreal c, const QPoint & p )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns the QPoint formed by multiplying both components of p by c.

Note that the result is rounded to the nearest integer as points are held as integers.

See also QPointF.

### const QPoint operator+ ( const QPoint & p1, const QPoint & p2 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns the sum of p1 and p2; each component is added separately.

### const QPoint operator- ( const QPoint & p1, const QPoint & p2 )

Returns p2 subtracted from p1; each component is subtracted separately.

### const QPoint operator- ( const QPoint & p )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns the QPoint formed by changing the sign of both components of p, equivalent to `QPoint(0,0) - p`.

### const QPoint operator/ ( const QPoint & p, qreal c )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns the QPoint formed by dividing both components of p by c.

Note that the result is rounded to the nearest integer as points are held as integers.

See also QPointF.

### QDataStream & operator<< ( QDataStream & s, const QPoint & p )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Writes point p to the stream s and returns a reference to the stream.

See also Format of the QDataStream operators.

### bool operator== ( const QPoint & p1, const QPoint & p2 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns true if p1 and p2 are equal; otherwise returns false.

### QDataStream & operator>> ( QDataStream & s, QPoint & p )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Reads a QPoint from the stream s into point p and returns a reference to the stream.

See also Format of the QDataStream operators.