# QPoint Class

The QPoint class defines a point in the plane using integer precision. More...

Header: | #include <QPoint> |

qmake: | QT += core |

**Note:** All functions in this class are reentrant.

## 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*=(float factor) |

QPoint & | operator*=(double factor) |

QPoint & | operator*=(int factor) |

QPoint & | operator+=(const QPoint & point) |

QPoint & | operator-=(const QPoint & point) |

QPoint & | operator/=(qreal divisor) |

## Static Public Members

int | dotProduct(const QPoint & p1, const QPoint & p2) |

## Related Non-Members

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

const QPoint | operator*(const QPoint & point, float factor) |

const QPoint | operator*(const QPoint & point, double factor) |

const QPoint | operator*(const QPoint & point, int factor) |

const QPoint | operator*(float factor, const QPoint & point) |

const QPoint | operator*(double factor, const QPoint & point) |

const QPoint | operator*(int factor, const QPoint & point) |

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

const QPoint | operator+(const QPoint & point) |

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

const QPoint | operator-(const QPoint & point) |

const QPoint | operator/(const QPoint & point, qreal divisor) |

QDataStream & | operator<<(QDataStream & stream, const QPoint & point) |

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

QDataStream & | operator>>(QDataStream & stream, QPoint & point) |

## Detailed Description

The QPoint class defines a point in the plane using integer precision.

A point is specified by a x coordinate and an y coordinate which can be accessed using the x() and y() functions. The isNull() function returns `true`

if both x and y are set to 0. The coordinates can be set (or altered) using the setX() and setY() functions, or alternatively the rx() and ry() functions which return references to the coordinates (allowing direct manipulation).

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

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

A QPoint object can also be used as a vector: Addition and subtraction are defined as for vectors (each component is added separately). A QPoint object can also be divided or multiplied by an `int`

or a `qreal`

.

In addition, the QPoint class provides the manhattanLength() function which gives an inexpensive approximation of the length of the QPoint object interpreted as a vector. Finally, QPoint objects can be streamed as well as compared.

**See also **QPointF and QPolygon.

## Member Function Documentation

### QPoint::QPoint()

Constructs a null point, i.e. with coordinates (0, 0)

**See also **isNull().

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

Constructs a point with the given coordinates (*xpos*, *ypos*).

`[static] `

int QPoint::dotProduct(const QPoint &* p1*, const QPoint &* p2*)

QPoint p( 3, 7); QPoint q(-1, 4); int lengthSquared = QPoint::dotProduct(p, q); // lengthSquared becomes 25

Returns the dot product of *p1* and *p2*.

This function was introduced in Qt 5.1.

### bool QPoint::isNull() const

Returns `true`

if both the x and y coordinates are set to 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. For example:

QPoint oldPosition; MyWidget::mouseMoveEvent(QMouseEvent *event) { QPoint point = event->pos() - oldPosition; if (point.manhattanLength() > 3) // the mouse has moved more than 3 pixels since the oldPosition }

This is a useful, and quick to calculate, approximation to the true length:

double trueLength = std::sqrt(std::pow(x(), 2) + std::pow(y(), 2));

The tradition of "Manhattan length" arises because such distances apply to travelers who can only travel on a rectangular grid, like the streets of Manhattan.

### int & QPoint::rx()

Returns a reference to the x coordinate of this point.

Using a reference makes it possible to directly manipulate x. For example:

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

### int & QPoint::ry()

Returns a reference to the y coordinate of this point.

Using a reference makes it possible to directly manipulate y. For example:

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

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

Sets the x coordinate of this point to the given *x* coordinate.

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

Sets the y coordinate of this point to the given *y* coordinate.

### int QPoint::x() const

Returns the x coordinate of this point.

### int QPoint::y() const

Returns the y coordinate of this point.

### QPoint & QPoint::operator*=(float* factor*)

Multiplies this point's coordinates by the given *factor*, and returns a reference to this point.

Note that the result is rounded to the nearest integer as points are held as integers. Use QPointF for floating point accuracy.

**See also **operator/=().

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

Multiplies this point's coordinates by the given *factor*, and returns a reference to this point. For 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. Use QPointF for floating point accuracy.

**See also **operator/=().

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

Multiplies this point's coordinates by the given *factor*, and returns a reference to this point.

**See also **operator/=().

### QPoint & QPoint::operator+=(const QPoint &* point*)

Adds the given *point* to this point and returns a reference to this point. For example:

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

**See also **operator-=().

### QPoint & QPoint::operator-=(const QPoint &* point*)

Subtracts the given *point* from this point and returns a reference to this point. For example:

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

**See also **operator+=().

### QPoint & QPoint::operator/=(qreal* divisor*)

This is an overloaded function.

Divides both x and y by the given *divisor*, and returns a reference to this point. For 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. Use QPointF for floating point accuracy.

**See also **operator*=().

## Related Non-Members

### 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 &* point*, float* factor*)

Returns a copy of the given *point* multiplied by the given *factor*.

**See also **QPoint::operator*=().

### const QPoint operator*(const QPoint &* point*, double* factor*)

Returns a copy of the given *point* multiplied by the given *factor*.

**See also **QPoint::operator*=().

### const QPoint operator*(const QPoint &* point*, int* factor*)

Returns a copy of the given *point* multiplied by the given *factor*.

**See also **QPoint::operator*=().

### const QPoint operator*(float* factor*, const QPoint &* point*)

This is an overloaded function.

Returns a copy of the given *point* multiplied by the given *factor*.

**See also **QPoint::operator*=().

### const QPoint operator*(double* factor*, const QPoint &* point*)

This is an overloaded function.

Returns a copy of the given *point* multiplied by the given *factor*.

**See also **QPoint::operator*=().

### const QPoint operator*(int* factor*, const QPoint &* point*)

This is an overloaded function.

Returns a copy of the given *point* multiplied by the given *factor*.

**See also **QPoint::operator*=().

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

Returns a QPoint object that is the sum of the given points, *p1* and *p2*; each component is added separately.

**See also **QPoint::operator+=().

### const QPoint operator+(const QPoint &* point*)

Returns *point* unmodified.

This function was introduced in Qt 5.0.

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

Returns a QPoint object that is formed by subtracting *p2* from *p1*; each component is subtracted separately.

**See also **QPoint::operator-=().

### const QPoint operator-(const QPoint &* point*)

This is an overloaded function.

Returns a QPoint object that is formed by changing the sign of both components of the given *point*.

Equivalent to `QPoint(0,0) - point`

.

### const QPoint operator/(const QPoint &* point*, qreal* divisor*)

Returns the QPoint formed by dividing both components of the given *point* by the given *divisor*.

**See also **QPoint::operator/=().

### QDataStream & operator<<(QDataStream &* stream*, const QPoint &* point*)

Writes the given *point* to the given *stream* and returns a reference to the stream.

**See also **Serializing Qt Data Types.

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

Returns `true`

if *p1* and *p2* are equal; otherwise returns false.

### QDataStream & operator>>(QDataStream &* stream*, QPoint &* point*)

Reads a point from the given *stream* into the given *point* and returns a reference to the stream.

**See also **Serializing Qt Data Types.

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