QLCDNumber Class

The QLCDNumber widget displays a number with LCD-like digits. More...

Header: #include <QLCDNumber>
qmake: QT += widgets
Inherits: QFrame

Public Types

enum Mode { Hex, Dec, Oct, Bin }
enum SegmentStyle { Outline, Filled, Flat }

Properties

  • 6 properties inherited from QFrame
  • 58 properties inherited from QWidget
  • 1 property inherited from QObject

Public Functions

QLCDNumber(QWidget *parent = Q_NULLPTR)
QLCDNumber(uint numDigits, QWidget *parent = Q_NULLPTR)
~QLCDNumber()
bool checkOverflow(double num) const
bool checkOverflow(int num) const
int digitCount() const
int intValue() const
Mode mode() const
SegmentStyle segmentStyle() const
void setDigitCount(int numDigits)
void setMode(Mode)
void setSegmentStyle(SegmentStyle)
bool smallDecimalPoint() const
double value() const

Reimplemented Public Functions

virtual QSize sizeHint() const
  • 14 public functions inherited from QFrame
  • 211 public functions inherited from QWidget
  • 31 public functions inherited from QObject
  • 14 public functions inherited from QPaintDevice

Public Slots

void display(const QString &s)
void display(int num)
void display(double num)
void setBinMode()
void setDecMode()
void setHexMode()
void setOctMode()
void setSmallDecimalPoint(bool)
  • 19 public slots inherited from QWidget
  • 1 public slot inherited from QObject

Signals

void overflow()

Reimplemented Protected Functions

virtual bool event(QEvent *e)
virtual void paintEvent(QPaintEvent *)
  • 4 protected functions inherited from QFrame
  • 35 protected functions inherited from QWidget
  • 9 protected functions inherited from QObject
  • 1 protected function inherited from QPaintDevice

Additional Inherited Members

  • 5 static public members inherited from QWidget
  • 11 static public members inherited from QObject
  • 4 protected functions inherited from QFrame
  • 35 protected functions inherited from QWidget
  • 9 protected functions inherited from QObject
  • 1 protected function inherited from QPaintDevice
  • 1 protected slot inherited from QWidget

Detailed Description

The QLCDNumber widget displays a number with LCD-like digits.

It can display a number in just about any size. It can display decimal, hexadecimal, octal or binary numbers. It is easy to connect to data sources using the display() slot, which is overloaded to take any of five argument types.

There are also slots to change the base with setMode() and the decimal point with setSmallDecimalPoint().

QLCDNumber emits the overflow() signal when it is asked to display something beyond its range. The range is set by setDigitCount(), but setSmallDecimalPoint() also influences it. If the display is set to hexadecimal, octal or binary, the integer equivalent of the value is displayed.

These digits and other symbols can be shown: 0/O, 1, 2, 3, 4, 5/S, 6, 7, 8, 9/g, minus, decimal point, A, B, C, D, E, F, h, H, L, o, P, r, u, U, Y, colon, degree sign (which is specified as single quote in the string) and space. QLCDNumber substitutes spaces for illegal characters.

It is not possible to retrieve the contents of a QLCDNumber object, although you can retrieve the numeric value with value(). If you really need the text, we recommend that you connect the signals that feed the display() slot to another slot as well and store the value there.

Incidentally, QLCDNumber is the very oldest part of Qt, tracing its roots back to a BASIC program on the Sinclair Spectrum.

Screenshot of a Windows style LCD number widget Screenshot of a Windows Vista style LCD number widget Screenshot of a Macintosh style LCD number widget Screenshot of a Fusion style LCD number widget
LCD number widgets shown in various widget styles (from left to right): Windows, Windows Vista, Macintosh, Fusion.

See also QLabel, QFrame, Digital Clock Example, and Tetrix Example.

Member Type Documentation

enum QLCDNumber::Mode

This type determines how numbers are shown.

ConstantValueDescription
QLCDNumber::Hex0Hexadecimal
QLCDNumber::Dec1Decimal
QLCDNumber::Oct2Octal
QLCDNumber::Bin3Binary

If the display is set to hexadecimal, octal or binary, the integer equivalent of the value is displayed.

enum QLCDNumber::SegmentStyle

This type determines the visual appearance of the QLCDNumber widget.

ConstantValueDescription
QLCDNumber::Outline0gives raised segments filled with the background color.
QLCDNumber::Filled1gives raised segments filled with the windowText color.
QLCDNumber::Flat2gives flat segments filled with the windowText color.

Property Documentation

digitCount : int

This property holds the current number of digits displayed.

Corresponds to the current number of digits. If QLCDNumber::smallDecimalPoint is false, the decimal point occupies one digit position.

By default, this property contains a value of 5.

This property was introduced in Qt 4.6.

Access functions:

int digitCount() const
void setDigitCount(int numDigits)

See also smallDecimalPoint.

intValue : int

This property holds the displayed value rounded to the nearest integer.

This property corresponds to the nearest integer to the current value displayed by the LCDNumber. This is the value used for hexadecimal, octal and binary modes.

If the displayed value is not a number, the property has a value of 0.

By default, this property contains a value of 0.

Access functions:

int intValue() const
void display(const QString &s)
void display(int num)
void display(double num)

mode : Mode

This property holds the current display mode (number base).

Corresponds to the current display mode, which is one of Bin, Oct, Dec (the default) and Hex. Dec mode can display floating point values, the other modes display the integer equivalent.

Access functions:

Mode mode() const
void setMode(Mode)

See also smallDecimalPoint(), setHexMode(), setDecMode(), setOctMode(), and setBinMode().

segmentStyle : SegmentStyle

This property holds the style of the LCDNumber.

StyleResult
OutlineProduces raised segments filled with the background color
Filled (this is the default).Produces raised segments filled with the foreground color.
FlatProduces flat segments filled with the foreground color.

Outline and Filled will additionally use QPalette::light() and QPalette::dark() for shadow effects.

Access functions:

SegmentStyle segmentStyle() const
void setSegmentStyle(SegmentStyle)

smallDecimalPoint : bool

This property holds the style of the decimal point.

If true the decimal point is drawn between two digit positions. Otherwise it occupies a digit position of its own, i.e. is drawn in a digit position. The default is false.

The inter-digit space is made slightly wider when the decimal point is drawn between the digits.

Access functions:

bool smallDecimalPoint() const
void setSmallDecimalPoint(bool)

See also mode.

value : double

This property holds the displayed value.

This property corresponds to the current value displayed by the LCDNumber.

If the displayed value is not a number, the property has a value of 0.

By default, this property contains a value of 0.

Access functions:

double value() const
void display(const QString &s)
void display(int num)
void display(double num)

Member Function Documentation

QLCDNumber::QLCDNumber(QWidget *parent = Q_NULLPTR)

Constructs an LCD number, sets the number of digits to 5, the base to decimal, the decimal point mode to 'small' and the frame style to a raised box. The segmentStyle() is set to Outline.

The parent argument is passed to the QFrame constructor.

See also setDigitCount() and setSmallDecimalPoint().

QLCDNumber::QLCDNumber(uint numDigits, QWidget *parent = Q_NULLPTR)

Constructs an LCD number, sets the number of digits to numDigits, the base to decimal, the decimal point mode to 'small' and the frame style to a raised box. The segmentStyle() is set to Filled.

The parent argument is passed to the QFrame constructor.

See also setDigitCount() and setSmallDecimalPoint().

QLCDNumber::~QLCDNumber()

Destroys the LCD number.

bool QLCDNumber::checkOverflow(double num) const

Returns true if num is too big to be displayed in its entirety; otherwise returns false.

See also display(), digitCount(), and smallDecimalPoint().

bool QLCDNumber::checkOverflow(int num) const

This is an overloaded function.

Returns true if num is too big to be displayed in its entirety; otherwise returns false.

See also display(), digitCount(), and smallDecimalPoint().

int QLCDNumber::digitCount() const

Returns the current number of digits.

Note: Getter function for property digitCount.

See also setDigitCount().

[slot] void QLCDNumber::display(const QString &s)

Displays the number represented by the string s.

This version of the function disregards mode() and smallDecimalPoint().

These digits and other symbols can be shown: 0/O, 1, 2, 3, 4, 5/S, 6, 7, 8, 9/g, minus, decimal point, A, B, C, D, E, F, h, H, L, o, P, r, u, U, Y, colon, degree sign (which is specified as single quote in the string) and space. QLCDNumber substitutes spaces for illegal characters.

Note: Setter function for property value. Setter function for property intValue.

[slot] void QLCDNumber::display(int num)

This is an overloaded function.

Displays the number num.

Note: Setter function for property value. Setter function for property intValue.

[slot] void QLCDNumber::display(double num)

This is an overloaded function.

Displays the number num.

Note: Setter function for property value. Setter function for property intValue.

[virtual protected] bool QLCDNumber::event(QEvent *e)

Reimplemented from QObject::event().

[signal] void QLCDNumber::overflow()

This signal is emitted whenever the QLCDNumber is asked to display a too-large number or a too-long string.

It is never emitted by setDigitCount().

[virtual protected] void QLCDNumber::paintEvent(QPaintEvent *)

Reimplemented from QWidget::paintEvent().

[slot] void QLCDNumber::setBinMode()

Calls setMode(Bin). Provided for convenience (e.g. for connecting buttons to it).

See also setMode(), setHexMode(), setDecMode(), setOctMode(), and mode().

[slot] void QLCDNumber::setDecMode()

Calls setMode(Dec). Provided for convenience (e.g. for connecting buttons to it).

See also setMode(), setHexMode(), setOctMode(), setBinMode(), and mode().

void QLCDNumber::setDigitCount(int numDigits)

Sets the current number of digits to numDigits. Must be in the range 0..99.

Note: Setter function for property digitCount.

See also digitCount().

[slot] void QLCDNumber::setHexMode()

Calls setMode(Hex). Provided for convenience (e.g. for connecting buttons to it).

See also setMode(), setDecMode(), setOctMode(), setBinMode(), and mode().

[slot] void QLCDNumber::setOctMode()

Calls setMode(Oct). Provided for convenience (e.g. for connecting buttons to it).

See also setMode(), setHexMode(), setDecMode(), setBinMode(), and mode().

[virtual] QSize QLCDNumber::sizeHint() const

Reimplemented from QWidget::sizeHint().

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