ICU4C

ICU4C is the C and C++ API of the International Components for Unicode (ICU) library. It provides a portable, data-driven set of services for Unicode text processing and globalization, enabling software to handle Unicode strings, normalize text, perform locale-sensitive sorting, formatting, and conversions across languages and scripts. The library is designed to be platform-independent and reusable across applications and systems.

Core capabilities include Unicode string handling (UTF-16 based APIs and related utilities), normalization, case mapping, character properties, bidirectional text processing, regular expressions, and transliteration. It offers locale-aware collation rules, and extensive support for formatting dates, times, numbers, currencies, and calendars according to international conventions. ICU4C also provides resource bundles and locale data to support language and region-specific behavior.

ICU4C relies on data packages, including ICU data files (like icudt*.dat) and data derived from the Unicode CLDR and Unicode Character Database. The project uses a data-driven design, allowing runtime locale and rule updates without recompiling code. It supports a wide range of platforms including Windows, Linux, macOS, and major mobile and embedded environments.

ICU4C originated from IBM's work on Unicode support and is now maintained by the ICU Project, a collaborative effort of contributors from industry and academia. It is released under an open-source ICU License (a permissive license) and is widely used in software requiring robust internationalization support.