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[править] QFont Class Reference
[модуль QtGui ]

The QFont class specifies a font used for drawing text. More... 

 #include <QFont>

[править] Открытые типы

  • enum Stretch { UltraCondensed, ExtraCondensed, Condensed, SemiCondensed, ..., UltraExpanded }
  • enum Style { StyleNormal, StyleItalic, StyleOblique }
  • enum StyleHint { AnyStyle, SansSerif, Helvetica, Serif, ..., System }
  • enum StyleStrategy { PreferDefault, PreferBitmap, PreferDevice, PreferOutline, ..., PreferQuality }
  • enum Weight { Light, Normal, DemiBold, Bold, Black }

[править] Открытые функции

[править] Статические открытые члены

[править] Связанные не-члены

  • QDataStream & operator<< ( QDataStream & s, const QFont & font )
  • QDataStream & operator>> ( QDataStream & s, QFont & font )

[править] Подробное описание

The QFont class specifies a font used for drawing text.

When you create a QFont object you specify various attributes that you want the font to have. Qt will use the font with the specified attributes, or if no matching font exists, Qt will use the closest matching installed font. The attributes of the font that is actually used are retrievable from a QFontInfo object. If the window system provides an exact match exactMatch() returns true. Use QFontMetrics to get measurements, e.g. the pixel length of a string using QFontMetrics::width().

Use QApplication::setFont() to set the application's default font.

If a chosen font does not include all the characters that need to be displayed, QFont will try to find the characters in the nearest equivalent fonts. When a QPainter draws a character from a font the QFont will report whether or not it has the character; if it does not, QPainter will draw an unfilled square.

Create QFonts like this: 

 QFont serifFont("Times", 10, QFont::Bold);
 QFont sansFont("Helvetica [Cronyx]", 12);

The attributes set in the constructor can also be set later, e.g. setFamily(), setPointSize(), setPointSizeFloat(), setWeight() and setItalic(). The remaining attributes must be set after contstruction, e.g. setBold(), setUnderline(), setOverline(), setStrikeOut() and setFixedPitch(). QFontInfo objects should be created after the font's attributes have been set. A QFontInfo object will not change, even if you change the font's attributes. The corresponding "get" functions, e.g. family(), pointSize(), etc., return the values that were set, even though the values used may differ. The actual values are available from a QFontInfo object.

If the requested font family is unavailable you can influence the font matching algorithm by choosing a particular QFont::StyleHint and QFont::StyleStrategy with setStyleHint(). The default family (corresponding to the current style hint) is returned by defaultFamily().

The font-matching algorithm has a lastResortFamily() and lastResortFont() in cases where a suitable match cannot be found. You can provide substitutions for font family names using insertSubstitution() and insertSubstitutions(). Substitutions can be removed with removeSubstitution(). Use substitute() to retrieve a family's first substitute, or the family name itself if it has no substitutes. Use substitutes() to retrieve a list of a family's substitutes (which may be empty).

Every QFont has a key() which you can use, for example, as the key in a cache or dictionary. If you want to store a user's font preferences you could use QSettings, writing the font information with toString() and reading it back with fromString(). The operator<<() and operator>>() functions are also available, but they work on a data stream.

It is possible to set the height of characters shown on the screen to a specified number of pixels with setPixelSize(); however using setPointSize() has a similar effect and provides device independence.

Under X11 you can set a font using its system specific name with setRawName().

Loading fonts can be expensive, especially on X11. QFont contains extensive optimizations to make the copying of QFont objects fast, and to cache the results of the slow window system functions it depends upon.

The font matching algorithm works as follows:

  1. The specified font family is searched for.
  2. If not found, the styleHint() is used to select a replacement family.
  3. Each replacement font family is searched for.
  4. If none of these are found or there was no styleHint(), "helvetica" will be searched for.
  5. If "helvetica" isn't found Qt will try the lastResortFamily().
  6. If the lastResortFamily() isn't found Qt will try the lastResortFont() which will always return a name of some kind.

Note that the actual font matching algorithm varies from platform to platform.

Once a font is found, the remaining attributes are matched in order of priority:

  1. fixedPitch()
  2. pointSize() (see below)
  3. weight()
  4. style()

If you have a font which matches on family, even if none of the other attributes match, this font will be chosen in preference to a font which doesn't match on family but which does match on the other attributes. This is because font family is the dominant search criteria.

The point size is defined to match if it is within 20% of the requested point size. When several fonts match and are only distinguished by point size, the font with the closest point size to the one requested will be chosen.

The actual family, font size, weight and other font attributes used for drawing text will depend on what's available for the chosen family under the window system. A QFontInfo object can be used to determine the actual values used for drawing the text.

Examples: 

 QFont f("Helvetica");

If you had both an Adobe and a Cronyx Helvetica, you might get either. 

 QFont f("Helvetica [Cronyx]");

You can specify the foundry you want in the family name. The font f in the above example will be set to "Helvetica [Cronyx]".

To determine the attributes of the font actually used in the window system, use a QFontInfo object, e.g. 

 QFontInfo info(f1);
 QString family = info.family();

To find out font metrics use a QFontMetrics object, e.g. 

 QFontMetrics fm(f1);
 int textWidthInPixels = fm.width("How many pixels wide is this text?");
 int textHeightInPixels = fm.height();

For more general information on fonts, see the comp.fonts FAQ. Information on encodings can be found from Roman Czyborra's page.

See also QFontComboBox, QFontMetrics, QFontInfo, QFontDatabase, and Character Map Example.

[править] Описание типов членов

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enum QFont::Stretch

Predefined stretch values that follow the CSS naming convention. The higher the value, the more stretched the text is.


Constant Value Description
QFont::UltraCondensed 50 50
QFont::ExtraCondensed 62 62
QFont::Condensed 75 75
QFont::SemiCondensed 87 87
QFont::Unstretched 100 100
QFont::SemiExpanded 112 112
QFont::Expanded 125 125
QFont::ExtraExpanded 150 150
QFont::UltraExpanded 200 200

See also setStretch() and stretch().

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enum QFont::Style

This enum describes the different styles of glyphs that are used to display text.


Constant Value Description
QFont::StyleNormal 0 Normal glyphs used in unstyled text.
QFont::StyleItalic 1 Italic glyphs that are specifically designed for the purpose of representing italicized text.
QFont::StyleOblique 2 Glyphs with an italic appearance that are typically based on the unstyled glyphs, but are not fine-tuned for the purpose of representing italicized text.

See also Weight.

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enum QFont::StyleHint

Style hints are used by the font matching algorithm to find an appropriate default family if a selected font family is not available.


Constant Value Description
QFont::AnyStyle  ? leaves the font matching algorithm to choose the family. This is the default.
QFont::SansSerif Helvetica the font matcher prefer sans serif fonts.
QFont::Helvetica 0 is a synonym for SansSerif.
QFont::Serif Times the font matcher prefers serif fonts.
QFont::Times  ? is a synonym for Serif.
QFont::TypeWriter Courier the font matcher prefers fixed pitch fonts.
QFont::Courier  ? a synonym for TypeWriter.
QFont::OldEnglish  ? the font matcher prefers decorative fonts.
QFont::Decorative OldEnglish is a synonym for OldEnglish.
QFont::System  ? the font matcher prefers system fonts.

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enum QFont::StyleStrategy

The style strategy tells the font matching algorithm what type of fonts should be used to find an appropriate default family.

The following strategies are available:


Constant Value Description
QFont::PreferDefault 0x0001 the default style strategy. It does not prefer any type of font.
QFont::PreferBitmap 0x0002 prefers bitmap fonts (as opposed to outline fonts).
QFont::PreferDevice 0x0004 prefers device fonts.
QFont::PreferOutline 0x0008 prefers outline fonts (as opposed to bitmap fonts).
QFont::ForceOutline 0x0010 forces the use of outline fonts.
QFont::NoAntialias 0x0100 don't antialias the fonts.
QFont::PreferAntialias 0x0080 antialias if possible.
QFont::OpenGLCompatible 0x0200 forces the use of OpenGL compatible fonts.
QFont::NoFontMerging 0x8000 If a font does not contain a character requested to draw then Qt automatically chooses a similar looking for that contains the character. This flag disables this feature.

Any of these may be OR-ed with one of these flags:


Constant Value Description
QFont::PreferMatch 0x0020 prefer an exact match. The font matcher will try to use the exact font size that has been specified.
QFont::PreferQuality 0x0040 prefer the best quality font. The font matcher will use the nearest standard point size that the font supports.

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enum QFont::Weight

Qt uses a weighting scale from 0 to 99 similar to, but not the same as, the scales used in Windows or CSS. A weight of 0 is ultralight, whilst 99 will be an extremely black.

This enum contains the predefined font weights:


Constant Value Description
QFont::Light 25 25
QFont::Normal 50 50
QFont::DemiBold 63 63
QFont::Bold 75 75
QFont::Black 87 87

[править] Описание функций-членов

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QFont::QFont ()

Constructs a font object that uses the application's default font.

See also QApplication::setFont() and QApplication::font().

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QFont::QFont ( const QString & family, int pointSize = -1, int weight = -1, bool italic = false )

Constructs a font object with the specified family, pointSize, weight and italic settings.

If pointSize is <= 0, it is set to 12.

The family name may optionally also include a foundry name, e.g. "Helvetica [Cronyx]". If the family is available from more than one foundry and the foundry isn't specified, an arbitrary foundry is chosen. If the family isn't available a family will be set using the font matching algorithm.

See also Weight, setFamily(), setPointSize(), setWeight(), setItalic(), setStyleHint(), and QApplication::font().

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QFont::QFont ( const QFont & font, QPaintDevice * pd )

Constructs a font from font for use on the paint device pd.

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QFont::QFont ( const QFont & font )

Constructs a font that is a copy of font.

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QFont::~QFont ()

Destroys the font object and frees all allocated resources.

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bool QFont::bold () const

Returns true if weight() is a value greater than QFont::Normal; otherwise returns false.

See also weight(), setBold(), and QFontInfo::bold().

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QString QFont::defaultFamily () const

Returns the family name that corresponds to the current style hint.

See also StyleHint, styleHint(), and setStyleHint().

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bool QFont::exactMatch () const

Returns true if a window system font exactly matching the settings of this font is available.

See also QFontInfo.

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QString QFont::family () const

Returns the requested font family name, i.e. the name set in the constructor or the last setFont() call.

See also setFamily(), substitutes(), and substitute().

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bool QFont::fixedPitch () const

Returns true if fixed pitch has been set; otherwise returns false.

See also setFixedPitch() and QFontInfo::fixedPitch().

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FT_Face QFont::freetypeFace () const

Returns the handle to the primary freetype face of the font. I font merging is not disabled a QFont can contain several physical fonts.

Returns 0 if the font does not contains a freetype face.

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bool QFont::fromString ( const QString & descrip )

Sets this font to match the description descrip. The description is a comma-separated list of the font attributes, as returned by toString().

See also toString().

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HFONT QFont::handle () const

Returns the window system handle to the font, for low-level access. Using this function is not portable.

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void QFont::insertSubstitution ( const QString & familyName, const QString & substituteName ) [static]

Inserts substituteName into the substitution table for the family familyName.

See also insertSubstitutions(), removeSubstitution(), substitutions(), substitute(), and substitutes().

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void QFont::insertSubstitutions ( const QString & familyName, const QStringList & substituteNames ) [static]

Inserts the list of families substituteNames into the substitution list for familyName.

See also insertSubstitution(), removeSubstitution(), substitutions(), and substitute().

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bool QFont::isCopyOf ( const QFont & f ) const

Returns true if this font and f are copies of each other, i.e. one of them was created as a copy of the other and neither has been modified since. This is much stricter than equality.

See also operator=() and operator==().

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bool QFont::italic () const

Returns true if the style() of the font is not QFont::StyleNormal

See also setItalic() and style().

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bool QFont::kerning () const

Returns true if kerning should be used when drawing text with this font.

See also setKerning().

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QString QFont::key () const

Returns the font's key, a textual representation of a font. It is typically used as the key for a cache or dictionary of fonts.

See also QMap.

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QString QFont::lastResortFamily () const

Returns the "last resort" font family name.

The current implementation tries a wide variety of common fonts, returning the first one it finds. Is is possible that no family is found in which case an empty string is returned.

See also lastResortFont().

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QString QFont::lastResortFont () const

Returns a "last resort" font name for the font matching algorithm. This is used if the last resort family is not available. It will always return a name, if necessary returning something like "fixed" or "system".

The current implementation tries a wide variety of common fonts, returning the first one it finds. The implementation may change at any time, but this function will always return a string containing something.

It is theoretically possible that there really isn't a lastResortFont() in which case Qt will abort with an error message. We have not been able to identify a case where this happens. Please report it as a bug if it does, preferably with a list of the fonts you have installed.

See also lastResortFamily() and rawName().

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quint32 QFont::macFontID () const

Returns an ATSUFontID

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bool QFont::overline () const

Returns true if overline has been set; otherwise returns false.

See also setOverline().

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int QFont::pixelSize () const

Returns the pixel size of the font if it was set with setPixelSize(). Returns -1 if the size was set with setPointSize() or setPointSizeF().

See also setPixelSize(), pointSize(), QFontInfo::pointSize(), and QFontInfo::pixelSize().

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int QFont::pointSize () const

Returns the point size of the font. Returns -1 if the font size was specified in pixels.

See also setPointSize() and pointSizeF().

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qreal QFont::pointSizeF () const

Returns the point size of the font. Returns -1 if the font size was specified in pixels.

See also pointSize(), setPointSizeF(), pixelSize(), QFontInfo::pointSize(), and QFontInfo::pixelSize().

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bool QFont::rawMode () const

Returns true if raw mode is used for font name matching; otherwise returns false.

See also setRawMode() and rawName().

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QString QFont::rawName () const

Returns the name of the font within the underlying window system.

On Windows and Mac OS X, this is usually just the family name of a TrueType font.

On X11, depending on whether Qt was built with FontConfig support, it is an XLFD (X Logical Font Description) or a FontConfig pattern. An XLFD may be returned even if FontConfig support is enabled.

Using the return value of this function is usually not portable.

See also setRawName().

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void QFont::removeSubstitution ( const QString & familyName ) [static]

Removes all the substitutions for familyName.

See also insertSubstitutions(), insertSubstitution(), substitutions(), and substitute().

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QFont QFont::resolve ( const QFont & other ) const

Returns a new QFont that has attributes copied from other that have not been previously set on this font.

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void QFont::setBold ( bool enable )

If enable is true sets the font's weight to QFont::Bold; otherwise sets the weight to QFont::Normal.

For finer boldness control use setWeight().

See also bold() and setWeight().

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void QFont::setFamily ( const QString & family )

Sets the family name of the font. The name is case insensitive and may include a foundry name.

The family name may optionally also include a foundry name, e.g. "Helvetica [Cronyx]". If the family is available from more than one foundry and the foundry isn't specified, an arbitrary foundry is chosen. If the family isn't available a family will be set using the font matching algorithm.

See also family(), setStyleHint(), and QFontInfo.

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void QFont::setFixedPitch ( bool enable )

If enable is true, sets fixed pitch on; otherwise sets fixed pitch off.

See also fixedPitch() and QFontInfo.

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void QFont::setItalic ( bool enable )

Sets the style() of the font to QFont::StyleItalic if enable is true; otherwise the style is set to QFont::StyleNormal.

See also italic() and QFontInfo.

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void QFont::setKerning ( bool enable )

Enables kerning for this font if enable is true; otherwise disables it. By default, kerning is enabled.

When kerning is enabled, glyph metrics do not add up anymore, even for Latin text. In other words, the assumption that width('a') + width('b') is equal to width("ab") is not neccesairly true.

See also kerning() and QFontMetrics.

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void QFont::setOverline ( bool enable )

If enable is true, sets overline on; otherwise sets overline off.

See also overline() and QFontInfo.

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void QFont::setPixelSize ( int pixelSize )

Sets the font size to pixelSize pixels.

Using this function makes the font device dependent. Use setPointSize() or setPointSizeF() to set the size of the font in a device independent manner.

See also pixelSize().

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void QFont::setPointSize ( int pointSize )

Sets the point size to pointSize. The point size must be greater than zero.

See also pointSize() and setPointSizeF().

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void QFont::setPointSizeF ( qreal pointSize )

Sets the point size to pointSize. The point size must be greater than zero. The requested precision may not be achieved on all platforms.

See also pointSizeF(), setPointSize(), and setPixelSize().

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void QFont::setRawMode ( bool enable )

If enable is true, turns raw mode on; otherwise turns raw mode off. This function only has an effect under X11.

If raw mode is enabled, Qt will search for an X font with a complete font name matching the family name, ignoring all other values set for the QFont. If the font name matches several fonts, Qt will use the first font returned by X. QFontInfo cannot be used to fetch information about a QFont using raw mode (it will return the values set in the QFont for all parameters, including the family name).

Warning: Do not use raw mode unless you really, really need it! In most (if not all) cases, setRawName() is a much better choice.

See also rawMode() and setRawName().

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void QFont::setRawName ( const QString & name )

Sets a font by its system specific name. The function is particularly useful under X, where system font settings (for example X resources) are usually available in XLFD (X Logical Font Description) form only. You can pass an XLFD as name to this function.

A font set with setRawName() is still a full-featured QFont. It can be queried (for example with italic()) or modified (for example with setItalic()) and is therefore also suitable for rendering rich text.

If Qt's internal font database cannot resolve the raw name, the font becomes a raw font with name as its family.

Note that the present implementation does not handle wildcards in XLFDs well, and that font aliases (file fonts.alias in the font directory on X11) are not supported.

See also rawName(), setRawMode(), and setFamily().

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void QFont::setStretch ( int factor )

Sets the stretch factor for the font.

The stretch factor changes the width of all characters in the font by factor percent. For example, setting factor to 150 results in all characters in the font being 1.5 times (ie. 150%) wider. The default stretch factor is 100. The minimum stretch factor is 1, and the maximum stretch factor is 4000.

The stretch factor is only applied to outline fonts. The stretch factor is ignored for bitmap fonts.

NOTE: QFont cannot stretch XLFD fonts. When loading XLFD fonts on X11, the stretch factor is matched against a predefined set of values for the SETWIDTH_NAME field of the XLFD.

See also stretch() and QFont::Stretch.

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void QFont::setStrikeOut ( bool enable )

If enable is true, sets strikeout on; otherwise sets strikeout off.

See also strikeOut() and QFontInfo.

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void QFont::setStyle ( Style style )

Sets the style of the font to style.

See also style(), italic(), and QFontInfo.

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void QFont::setStyleHint ( StyleHint hint, StyleStrategy strategy = PreferDefault )

Sets the style hint and strategy to hint and strategy, respectively.

If these aren't set explicitly the style hint will default to AnyStyle and the style strategy to PreferDefault.

Qt does not support style hints on X11 since this information is not provided by the window system.

See also StyleHint, styleHint(), StyleStrategy, styleStrategy(), and QFontInfo.

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void QFont::setStyleStrategy ( StyleStrategy s )

Sets the style strategy for the font to s.

See also styleStrategy() and QFont::StyleStrategy.

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void QFont::setUnderline ( bool enable )

If enable is true, sets underline on; otherwise sets underline off.

See also underline() and QFontInfo.

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void QFont::setWeight ( int weight )

Sets the weight the font to weight, which should be a value from the QFont::Weight enumeration.

See also weight() and QFontInfo.

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int QFont::stretch () const

Returns the stretch factor for the font.

See also setStretch().

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bool QFont::strikeOut () const

Returns true if strikeout has been set; otherwise returns false.

See also setStrikeOut().

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Style QFont::style () const

Returns the style of the font.

See also setStyle().

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StyleHint QFont::styleHint () const

Returns the StyleHint.

The style hint affects the font matching algorithm. See QFont::StyleHint for the list of available hints.

See also setStyleHint(), QFont::StyleStrategy, and QFontInfo::styleHint().

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StyleStrategy QFont::styleStrategy () const

Returns the StyleStrategy.

The style strategy affects the font matching algorithm. See QFont::StyleStrategy for the list of available strategies.

See also setStyleStrategy(), setStyleHint(), and QFont::StyleHint.

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QString QFont::substitute ( const QString & familyName ) [static]

Returns the first family name to be used whenever familyName is specified. The lookup is case insensitive.

If there is no substitution for familyName, familyName is returned.

To obtain a list of substitutions use substitutes().

See also setFamily(), insertSubstitutions(), insertSubstitution(), and removeSubstitution().

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QStringList QFont::substitutes ( const QString & familyName ) [static]

Returns a list of family names to be used whenever familyName is specified. The lookup is case insensitive.

If there is no substitution for familyName, an empty list is returned.

See also substitute(), insertSubstitutions(), insertSubstitution(), and removeSubstitution().

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QStringList QFont::substitutions () [static]

Returns a sorted list of substituted family names.

See also insertSubstitution(), removeSubstitution(), and substitute().

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QString QFont::toString () const

Returns a description of the font. The description is a comma-separated list of the attributes, perfectly suited for use in QSettings.

See also fromString().

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bool QFont::underline () const

Returns true if underline has been set; otherwise returns false.

See also setUnderline().

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int QFont::weight () const

Returns the weight of the font which is one of the enumerated values from QFont::Weight.

See also setWeight(), Weight, and QFontInfo.

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QFont::operator QVariant () const

Returns the font as a QVariant

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bool QFont::operator!= ( const QFont & f ) const

Returns true if this font is different from f; otherwise returns false.

Two QFonts are considered to be different if their font attributes are different. If rawMode() is enabled for both fonts, only the family fields are compared.

See also operator==().

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bool QFont::operator< ( const QFont & f ) const

Provides an arbitrary comparison of this font and font f. All that is guaranteed is that the operator returns false if both fonts are equal and that (f1 < f2) == !(f2 < f1) if the fonts are not equal.

This function is useful in some circumstances, for example if you want to use QFont objects as keys in a QMap.

See also operator==(), operator!=(), and isCopyOf().

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QFont & QFont::operator= ( const QFont & font )

Assigns font to this font and returns a reference to it.

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bool QFont::operator== ( const QFont & f ) const

Returns true if this font is equal to f; otherwise returns false.

Two QFonts are considered equal if their font attributes are equal. If rawMode() is enabled for both fonts, only the family fields are compared.

See also operator!=() and isCopyOf().

[править] Связанные не-члены

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QDataStream & operator<< ( QDataStream & s, const QFont & font )

This is an overloaded member function, provided for convenience.

Writes the font font to the data stream s. (toString() writes to a text stream.)

See also Format of the QDataStream operators.

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QDataStream & operator>> ( QDataStream & s, QFont & font )

This is an overloaded member function, provided for convenience.

Reads the font font from the data stream s. (fromString() reads from a text stream.)

See also Format of the QDataStream operators.

Copyright © 2007 Trolltech Trademarks
Qt 4.3.2
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