icu.net

Overview

icu-dotnet is the C# wrapper for a subset of ICU.

ICU is a mature, widely used set of C/C++ and Java libraries providing Unicode and Globalization support for software applications. ICU is widely portable and gives applications the same results on all platforms and between C/C++ and Java software.

Usage

This library provides .NET classes and methods for (a subset of) the ICU C API. Please refer to the ICU API documentation. In icu.net you'll find classes that correspond to the C++ classes of ICU4C.

Although not strictly required it is recommended to call Icu.Wrapper.Init() at the start of the application. This will allow to use icu.net from multiple threads (c.f. ICU Initialization and Termination). Similarly, it might be beneficial to call Icu.Wrapper.Cleanup() before exiting.

Sample code:

    static class Program
    {
        public static void Main(string[] args)
        {
            Icu.Wrapper.Init();
            // Will output "NFC form of XA\u0308bc is XÄbc"
            Console.WriteLine($"NFC form of XA\\u0308bc is {Icu.Normalizer.Normalize("XA\u0308bc",
                Icu.Normalizer.UNormalizationMode.UNORM_NFC)}");
            Icu.Wrapper.Cleanup();
        }
    }

Building

To build the current version of icu-dotnet you'll need .NET 8.0 or .NET 10.0 installed.

icu-dotnet can be built from the command line as well as Visual Studio or JetBrains Rider.

Running Unit Tests

You can build and run the unit tests by running:

dotnet test source/icu.net.sln

or, if wanting to run tests on just one specific .net version (v8.0 in this example):

dotnet test source/icu.net.sln -p:TargetFramework=net8.0

Linux and macOS

It is important for icu.net.dll.config to be bundled with your application when not running on Windows. If it doesn't copy reliably to the output directory, you might find adding something like the following to your csproj file will resolve the issue. Note that the version number in the path must match the version number of icu.net that is referenced in the project.

<ItemGroup>
  <None Update="$(NuGetPackageRoot)\icu.net\2.9.0\contentFiles\any\any\icu.net.dll.config">
    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
  </None>
</ItemGroup>

Docker

icu-dotnet depends on libc dynamic libraries at run time. If running within Docker, you may need to install them, for example:

FROM mcr.microsoft.com/dotnet/aspnet:3.1

# Install system dependencies.
RUN apt-get update \
    && apt-get install -y \
        # icu.net dependency: libdl.so
        libc6-dev \
     && rm -rf /var/lib/apt/lists/*

...

ICU versions

Linux

icu-dotnet links with any installed version of ICU shared objects. It is recommended to install the version provided by the distribution. For example:

OS	ICU
Ubuntu 22.04 (Jammy)	70
Ubuntu 24.04 (Noble)	74
Ubuntu 26.04 (Resolute)	78
Debian 12 (Bookworm)	72
Debian 13 (Trixie)	76

If the version provided by the Linux distribution doesn't match your needs, Microsoft's ICU package includes builds for Linux.

Windows

Rather than using the full version of ICU (which can be ~25 MB), a custom minimum build can be used. It can be installed by the Icu4c.Win.Min nuget package. The full version of ICU is also available as Icu4c.Win.Full.Lib and Icu4c.Win.Full.Bin.

Microsoft also makes the full version available as Microsoft.ICU.ICU4C.Runtime.

What's in the minimum build

• Characters
• ErrorCodes
• Locale
• Normalizer
• Rules-based Collator
• Unicode set to pattern conversions

macOS

macOS doesn't come preinstalled with all the normal icu4c libraries. They must be installed separately via a package manager such as Homebrew or MacPorts.

# Homebrew (more common)
brew install icu4c

# MacPorts
sudo port install icu

icu.net automatically searches the standard Homebrew and MacPorts installation directories, so no extra configuration is needed after installing via either package manager.

Troubleshooting

• make sure you added the nuget package icu.net and have native ICU libraries available.
• the binaries of the nuget packages need to be copied to your output directory. For icu.net this happens by the assembly reference that the package adds to your project. The binaries of Icu4c.Win.Min are only relevant on Windows. They will get copied by the Icu4c.Win.Min.targets file included in the nuget package.

On Windows, the package installer should have added an import to the *.csproj file similar to the following:

<Import Project="..\..\packages\Icu4c.Win.Min.54.1.31\build\Icu4c.Win.Min.targets"
    Condition="Exists('..\..\packages\Icu4c.Win.Min.54.1.31\build\Icu4c.Win.Min.targets')" />

Contributing

We love contributions! The library mainly contains the functionality we need for our products. If you miss something that is part of ICU4C but not yet wrapped in icu.net, add it and create a pull request.

If you find a bug - create an issue on GitHub, then preferably fix it and create a pull request!