Unicode in Qt

These classes are relevant when working with string data. For information about rendering text, see the Rich Text Processing overview, and if your string data is in XML, see the XML Processing overview.

• QAnyStringView: The QAnyStringView class provides a unified view on Latin-1, UTF-8, or UTF-16 strings with a read-only subset of the QString API.

• QByteArray: The QByteArray class provides an array of bytes.

• QByteArrayList: The QByteArrayList class provides a list of byte arrays.

• QByteArrayMatcher: The QByteArrayMatcher class holds a sequence of bytes that can be quickly matched in a byte array.

• QByteArrayView: The QByteArrayView class provides a view on an array of bytes with a read-only subset of the QByteArray API.

• QChar: The QChar class provides a 16-bit Unicode character.

• QCollator: The QCollator class compares strings according to a localized collation algorithm.

• QCollatorSortKey: The QCollatorSortKey class can be used to speed up string collation.

• QLatin1Char: The QLatin1Char class provides an 8-bit ASCII/Latin-1 character.

• QLatin1StringView: The QLatin1StringView class provides a thin wrapper around an US-ASCII/Latin-1 encoded string literal.

• QLocale: The QLocale class converts between numbers and their string representations in various languages.

• QStaticByteArrayMatcher: The QStaticByteArrayMatcher class is a compile-time version of QByteArrayMatcher.

• QString: The QString class provides a Unicode character string.

• QStringList: The QStringList class provides a list of strings.

• QStringMatcher: The QStringMatcher class holds a sequence of characters that can be quickly matched in a Unicode string.

• QStringRef: The QStringRef class provides a thin wrapper around QString substrings.

• QStringTokenizer: The QStringTokenizer class splits strings into tokens along given separators.

• QStringView: The QStringView class provides a unified view on UTF-16 strings with a read-only subset of the QString API.

• QTextBoundaryFinder: The QTextBoundaryFinder class provides a way of finding Unicode text boundaries in a string.

• QTextStream: The QTextStream class provides a convenient interface for reading and writing text.

• QUtf8StringView: The QUtf8StringView class provides a unified view on UTF-8 strings with a read-only subset of the QString API.

The Unicode Consortium has a number of documents available, including

• The current version of the standard

• A technical introduction to Unicode

• The home page for the standard

In Qt, and in most applications that use Qt, most or all user-visible strings are stored using Unicode. Qt provides:

• Translation to/from legacy encoding for file I/O: see QTextCodec and QTextStream.

• Support for locale specific Input Methods and keyboards.

• A string class, QString, that stores Unicode characters, with support for migrating from C strings including fast translation to and from UTF-8, ISO8859-1 and US-ASCII, and all the usual string operations.

• Unicode-aware UI controls.

• Unicode compliant text segmentation (QTextBoundaryFinder)

• Unicode compliant line breaking and text rendering

To fully benefit from Unicode, we recommend using QString for storing all user-visible strings, and performing all text file I/O using QTextStream.

All the function arguments in Qt that may be user-visible strings, QLabel::setText() and a many others, take const QString &s. QString provides implicit casting from const char * so that things like

label->setText("Password:");

will work. There is also a function, QObject::tr(), that provides translation support, like this:

label->setText(tr("Password:"));

QObject::tr() maps from const char * to a Unicode string, and uses installable QTranslator objects to do the mapping.

Qt provides a number of built-in QTextCodec classes, that is, classes that know how to translate between Unicode and legacy encodings to support programs that must talk to other programs or read/write files in legacy file formats.

Conversion to/from const char * uses a UTF-8. However, applications can easily find codecs for other locales, and set any open file or network connection to use a special codec.

Since US-ASCII and ISO-8859-1 are so common, there are also especially fast functions for mapping to and from them. For example, to open an application's icon one might do this:

QFile file(QString::fromLatin1("appicon.png"));

or

QFile file(QLatin1String("appicon.png"));

Qt supports rendering text in most languages written in the world. The detailed list of supported writing systems depends a bit on operating system support and font availability on the target system.

See also Internationalization with Qt