- Qt 5.3
- Unicode in Qt
- Qt 5.3.2 Reference Documentation

# Unicode in Qt

Unicode is the standard for encoding text in almost all languages spoken in the world. It is nowadays used as the native encoding for text on most modern operating systems. The major exception is Microsoft Windows that still has a dual system supporting code pages and Unicode for applications.

Qt 5.0 uses and fully supports version 6.2 of the Unicode standard.

## Qt's Classes for Working with Strings

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.

QTextStream | The QTextStream class provides a convenient interface for reading and writing text.
QByteArray | The QByteArray class provides an array of bytes.
QByteArrayMatcher | The QByteArrayMatcher class holds a sequence of bytes that can be quickly matched in a byte array.
QChar | The QChar class provides a 16-bit Unicode character.
QLatin1Char | The QLatin1Char class provides an 8-bit ASCII/Latin-1 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.
QLocale | The QLocale class converts between numbers and their string representations in various languages.
QLatin1String | The QLatin1String class provides a thin wrapper around an US-ASCII/Latin-1 encoded string literal.
QString | The QString class provides a Unicode character string.
QStringRef | The QStringRef class provides a thin wrapper around QString substrings.
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.
QTextBoundaryFinder | The QTextBoundaryFinder class provides a way of finding Unicode text boundaries in a string.

## Information about Unicode on the Web

The Unicode Consortium has a number of documents available, including

- The current version of the standard: Unicode 6.2.0.
- A technical introduction to Unicode
- The home page for the standard

## Unicode in Qt

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 encodings 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.