# qpoint.3qt - Man Page

Defines a point in the plane

## Synopsis

`#include <qpoint.h>`

### Public Members

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

## Description

The QPoint class defines a point in the plane.

A point is specified by an x coordinate and a y coordinate.

The coordinate type is `QCOORD` (a 32-bit integer). The minimum value of `QCOORD` is `QCOORD_MIN` (-2147483648) and the maximum value is `QCOORD_MAX` (2147483647).

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 `double`. 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.

## 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)).

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

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

Example:

```        QPoint p( -1, 4 );
p *= 2;            // p becomes (-2,8)```

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

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

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 truncated because points are held as integers.

## 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/= ( int c )

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

Example:

```        QPoint p( -2, 8 );
p /= 2;            // p becomes (-1,4)```

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

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

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 truncated because points are held as integers.

## QCOORD & 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)```

## QCOORD & 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)```

## void QPoint::setX ( int x )

Sets the x coordinate of the point to x.

Example: t14/cannon.cpp.

## void QPoint::setY ( int y )

Sets the y coordinate of the point to y.

Example: t14/cannon.cpp.

## int QPoint::x () const

Returns the x coordinate of the point.

Examples:

## int QPoint::y () const

Returns the y coordinate of the point.

Examples:

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

Returns TRUE if p1 and p2 are not equal; otherwise returns FALSE.

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

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

## const QPoint operator* ( int 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.

## const QPoint operator* ( const QPoint & p, double 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 truncated because points are held as integers.

## const QPoint operator* ( double 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 truncated because points are held as integers.

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

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, int c )

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

## const QPoint operator/ ( const QPoint & p, double 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 truncated because points are held as integers.

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

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

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

Returns TRUE if p1 and p2 are equal; otherwise returns FALSE.

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

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

## Author

Generated automatically from the source code.

## Bugs

If you find a bug in Qt, please report it as described in http://doc.trolltech.com/bughowto.html. Good bug reports help us to help you. Thank you.

The definitive Qt documentation is provided in HTML format; it is located at \$QTDIR/doc/html and can be read using Qt Assistant or with a web browser. This man page is provided as a convenience for those users who prefer man pages, although this format is not officially supported by Trolltech.

If you find errors in this manual page, please report them to qt-bugs@trolltech.com. Please include the name of the manual page (qpoint.3qt) and the Qt version (3.3.8).

## Referenced By

The man page QPoint.3qt(3) is an alias of qpoint.3qt(3).

2 February 2007 Trolltech AS