Tag Struct
struct QFont::TagThe QFont::Tag type provides access to advanced font features. More...
This struct was introduced in Qt 6.7.
Public Functions
| Tag() | |
| Tag(const char (&)[N] str) | |
| bool | isValid() const |
| QByteArray | toString() const |
| quint32 | value() const |
Static Public Members
| std::optional<QFont::Tag> | fromString(QAnyStringView view) |
| std::optional<QFont::Tag> | fromValue(quint32 value) |
Related Non-Members
| Qt::strong_ordering | compareThreeWay(const QFont::Tag &lhs, const QFont::Tag &rhs) |
| bool | comparesEqual(const QFont::Tag &lhs, const QFont::Tag &rhs) |
| size_t | qHash(QFont::Tag key, size_t seed = 0) |
Detailed Description
QFont provides access to advanced features when shaping text. A feature is defined by a tag, which can be represented as a four-character string, or as a 32bit integer value. This type represents such a tag in a type-safe way. It can be constructed from a four-character, 8bit string literal, or from a corresponding 32bit integer value. Using a shorter or longer string literal will result in a compile-time error.
QFont font; // Correct font.setFeature("frac"); // Wrong - won't compile font.setFeature("fraction"); // Wrong - will produce runtime warning and fail font.setFeature(u"fraction"_s);
The named constructors allow to create a tag from an 32bit integer or string value, and will return a std::nullopt when the input is invalid.
See also QFont::setFeature() and QFont::featureTags().
Member Function Documentation
[constexpr noexcept] Tag::Tag()
Default constructor, producing an invalid tag.
[constexpr noexcept] template <size_t N> Tag::Tag(const char (&)[N] str)
Constructs a tag from a string literal, str. The literal must be exactly four characters long.
font.setFeature("frac", 1);
See also fromString() and fromValue().
[static noexcept] std::optional<QFont::Tag> Tag::fromString(QAnyStringView view)
Returns a tag constructed from the string in view. The string must be exactly four characters long.
Returns std::nullopt if the input is not four characters long, or if the tag produced would be invalid.
See also isValid() and fromValue().
[static constexpr noexcept] std::optional<QFont::Tag> Tag::fromValue(quint32 value)
Returns a tag constructed from value, or std::nullopt if the tag produced would be invalid.
See also isValid().
[constexpr noexcept] bool Tag::isValid() const
Returns whether the tag is valid. A tag is valid if its value is not zero.
See also value(), fromValue(), and fromString().
QByteArray Tag::toString() const
Returns the string representation of this tag as a byte array.
See also fromString().
[constexpr noexcept] quint32 Tag::value() const
Returns the numerical value of this tag.
Related Non-Members
[constexpr noexcept] Qt::strong_ordering compareThreeWay(const QFont::Tag &lhs, const QFont::Tag &rhs)
[constexpr noexcept] bool comparesEqual(const QFont::Tag &lhs, const QFont::Tag &rhs)
Compare lhs with rhs for equality and ordering.
[constexpr noexcept] size_t qHash(QFont::Tag key, size_t seed = 0)
Returns the hash value for key, using seed to seed the calculation.