International Components for Unicode
ICU 50.2 ReadMe

Last updated: 2019-Apr-10
Copyright © 1997-2013 International Business Machines Corporation and others. All Rights Reserved.

Table of Contents

Introduction

Today's software market is a global one in which it is desirable to develop and maintain one application (single source/single binary) that supports a wide variety of languages. The International Components for Unicode (ICU) libraries provide robust and full-featured Unicode services on a wide variety of platforms to help this design goal. The ICU libraries provide support for:

ICU has a sister project ICU4J that extends the internationalization capabilities of Java to a level similar to ICU. The ICU C/C++ project is also called ICU4C when a distinction is necessary.

Getting started

This document describes how to build and install ICU on your machine. For other information about ICU please see the following table of links.
The ICU homepage also links to related information about writing internationalized software.

Here are some useful links regarding ICU and internationalization in general.
ICU, ICU4C & ICU4J Homepage http://icu-project.org/
FAQ - Frequently Asked Questions about ICU http://userguide.icu-project.org/icufaq
ICU User's Guide http://userguide.icu-project.org/
How To Use ICU http://userguide.icu-project.org/howtouseicu
Download ICU Releases http://site.icu-project.org/download
ICU4C API Documentation Online http://icu-project.org/apiref/icu4c/
Online ICU Demos http://demo.icu-project.org/icu-bin/icudemos
Contacts and Bug Reports/Feature Requests http://site.icu-project.org/contacts

Important: Please make sure you understand the Copyright and License Information.

What is new in this release?

To see which APIs are new or changed in this release, view the ICU4C API Change Report.

The following list concentrates on changes that affect existing applications migrating from previous ICU releases. For more news about this release, see the ICU milestone download page.

Thread safety support cannot be removed

ICU4C 50 dropped support for the --enable-threads/--disable-threads configure option and the uconfig.h ICU_USE_THREADS switch. ICU4C 50 and higher is always built with multi-threading safety support. ICU4C has never created threads in its libraries.

If you need to prevent ICU from using thread safe mutexes when your application does not create threads, then you can use the --enable-weak-threads configure option. The --enable-weak-threads configure option will cause ICU to weakly reference the pthread mutex functions, and the stub implementations in the C runtime will be used. If this configure option does not work on your platform, then you can call u_setMutexFunctions() and u_setAtomicIncDecFunctions() with your own empty implementations.

The default compilers have changed

ICU has changed the compilers chosen by default. If the clang and clang++ compilers are available, those will be used instead of gcc and g++. If the clang compilers are not available, then gcc and g++ will be used just as before. The clang++ compiler provides C++11 support and some optimizations that are helpful to ICU. The API remains the same between these two sets of compilers, but ICU can internally leverage language features and optimizations that are available in clang++.

If you need to force ICU to compile with gcc and g++, then you can use the following from the command line in the source directory:

./configure CC=gcc CXX=g++ CFLAGS=-O3 CXXFLAGS=-O3

C++ Collator subclassing-API breaking changes

We have made some changes to the C++ Collator API for ICU 50 that will make it easier to use and implement the Collator but which are incompatible for subclasses. If there are subclasses, they will have to be modified as well. It will be easy to adapt subclass source code, if there is any. We think it is unlikely (or at least rare) that users write subclasses of the C++ Collator, given the number of virtual methods and the complexities of a collation implementation.

For details see the email "ICU4C C++ Collator subclassing-API breaking changes" sent on 2012-jul-25 to the icu-design and icu-support mailing lists, and ICU ticket #9346, including the changes for that ticket.

In particular, the class TestCollator in source/test/intltest/apicoll.cpp illustrates how a subclass needs to be changed. However, note that the TestCollator was also simplified slightly; not all changes made there were strictly required for the API signature changes.

How To Download the Source Code

There are two ways to download ICU releases:

ICU Source Code Organization

In the descriptions below, <ICU> is the full path name of the ICU directory (the top level directory from the distribution archives) in your file system. You can also view the ICU Architectural Design section of the User's Guide to see which libraries you need for your software product. You need at least the data ([lib]icudt) and the common ([lib]icuuc) libraries in order to use ICU.

The following files describe the code drop.
File Description
readme.html Describes the International Components for Unicode (this file)
license.html Contains the text of the ICU license


The following directories contain source code and data files.
Directory Description
<ICU>/source/common/ The core Unicode and support functionality, such as resource bundles, character properties, locales, codepage conversion, normalization, Unicode properties, Locale, and UnicodeString.
<ICU>/source/i18n/ Modules in i18n are generally the more data-driven, that is to say resource bundle driven, components. These deal with higher-level internationalization issues such as formatting, collation, text break analysis, and transliteration.
<ICU>/source/layout/ Contains the ICU layout engine (not a rasterizer).
<ICU>/source/io/ Contains the ICU I/O library.
<ICU>/source/data/

This directory contains the source data in text format, which is compiled into binary form during the ICU build process. It contains several subdirectories, in which the data files are grouped by function. Note that the build process must be run again after any changes are made to this directory.

If some of the following directories are missing, it's probably because you got an official download. If you need the data source files for customization, then please download the ICU source code from subversion.

  • in/ A directory that contains a pre-built data library for ICU. A standard source code package will contain this file without several of the following directories. This is to simplify the build process for the majority of users and to reduce platform porting issues.
  • brkitr/ Data files for character, word, sentence, title casing and line boundary analysis.
  • locales/ These .txt files contain ICU language and culture-specific localization data. Two special bundles are root, which is the fallback data and parent of other bundles, and index, which contains a list of installed bundles. The makefile resfiles.mk contains the list of resource bundle files.
  • mappings/ Here are the code page converter tables. These .ucm files contain mappings to and from Unicode. These are compiled into .cnv files. convrtrs.txt is the alias mapping table from various converter name formats to ICU internal format and vice versa. It produces cnvalias.icu. The makefiles ucmfiles.mk, ucmcore.mk, and ucmebcdic.mk contain the list of converters to be built.
  • translit/ This directory contains transliterator rules as resource bundles, a makefile trnsfiles.mk containing the list of installed system translitaration files, and as well the special bundle translit_index which lists the system transliterator aliases.
  • unidata/ This directory contains the Unicode data files. Please see http://www.unicode.org/ for more information.
  • misc/ The misc directory contains other data files which did not fit into the above categories. Currently it only contains time zone information, and a name preperation file for IDNA.
  • out/ This directory contains the assembled memory mapped files.
  • out/build/ This directory contains intermediate (compiled) files, such as .cnv, .res, etc.

If you are creating a special ICU build, you can set the ICU_DATA environment variable to the out/ or the out/build/ directories, but this is generally discouraged because most people set it incorrectly. You can view the ICU Data Management section of the ICU User's Guide for details.
<ICU>/source/test/intltest/ A test suite including all C++ APIs. For information about running the test suite, see the build instructions specific to your platform later in this document.
<ICU>/source/test/cintltst/ A test suite written in C, including all C APIs. For information about running the test suite, see the build instructions specific to your platform later in this document.
<ICU>/source/test/iotest/ A test suite written in C and C++ to test the icuio library. For information about running the test suite, see the build instructions specific to your platform later in this document.
<ICU>/source/test/testdata/ Source text files for data, which are read by the tests. It contains the subdirectories out/build/ which is used for intermediate files, and out/ which contains testdata.dat.
<ICU>/source/tools/ Tools for generating the data files. Data files are generated by invoking <ICU>/source/data/build/makedata.bat on Win32 or <ICU>/source/make on UNIX.
<ICU>/source/samples/ Various sample programs that use ICU
<ICU>/source/extra/ Non-supported API additions. Currently, it contains the 'uconv' tool to perform codepage conversion on files.
<ICU>/packaging/ This directory contain scripts and tools for packaging the final ICU build for various release platforms.
<ICU>/source/config/ Contains helper makefiles for platform specific build commands. Used by 'configure'.
<ICU>/source/allinone/ Contains top-level ICU workspace and project files, for instance to build all of ICU under one MSVC project.
<ICU>/include/ Contains the headers needed for developing software that uses ICU on Windows.
<ICU>/lib/ Contains the import libraries for linking ICU into your Windows application.
<ICU>/bin/ Contains the libraries and executables for using ICU on Windows.

How To Build And Install ICU

Recommended Build Options

Depending on the platform and the type of installation, we recommend a small number of modifications and build options.

ICU as a System-Level Library

If ICU is installed as a system-level library, there are further opportunities and restrictions to consider. For details, see the Using ICU as an Operating System Level Library section of the User Guide ICU Architectural Design chapter.

User-Configurable Settings

ICU4C can be customized via a number of user-configurable settings. Many of them are controlled by preprocessor macros which are defined in the source/common/unicode/uconfig.h header file. Some turn off parts of ICU, for example conversion or collation, trading off a smaller library for reduced functionality. Other settings are recommended (see previous section) but their default values are set for better source code compatibility.

In order to change such user-configurable settings, you can either modify the uconfig.h header file by adding a specific #define ... for one or more of the macros before they are first tested, or set the compiler's preprocessor flags (CPPFLAGS) to include an equivalent -D macro definition.

How To Build And Install On Windows

Building International Components for Unicode requires:

The steps are:

  1. Unzip the icu-XXXX.zip file into any convenient location. Using command line zip, type "unzip -a icu-XXXX.zip -d drive:\directory", or just use WinZip.
  2. Be sure that the ICU binary directory, <ICU>\bin\, is included in the PATH environment variable. The tests will not work without the location of the ICU DLL files in the path.
  3. Open the "<ICU>\source\allinone\allinone.sln" workspace file in Microsoft Visual Studio. (This solution includes all the International Components for Unicode libraries, necessary ICU building tools, and the test suite projects). Please see the command line note below if you want to build from the command line instead.
  4. Set the active platform to "Win32" or "x64" (See Windows platform note below) and configuration to "Debug" or "Release" (See Windows configuration note below).
  5. Choose the "Build" menu and select "Rebuild Solution". If you want to build the Debug and Release at the same time, see the batch configuration note below.
  6. Run the tests. They can be run from the command line or from within Visual Studio.

    Running the Tests from the Windows Command Line (cmd)

    Running the Tests from within Visual Studio

    1. Run the C++ test suite, "intltest". To do this: set the active startup project to "intltest", and press Ctrl+F5 to run it. Make sure that it passes without any errors.
    2. Run the C test suite, "cintltst". To do this: set the active startup project to "cintltst", and press Ctrl+F5 to run it. Make sure that it passes without any errors.
    3. Run the I/O test suite, "iotest". To do this: set the active startup project to "iotest", and press Ctrl+F5 to run it. Make sure that it passes without any errors.
  7. You are now able to develop applications with ICU by using the libraries and tools in <ICU>\bin\. The headers are in <ICU>\include\ and the link libraries are in <ICU>\lib\. To install the ICU runtime on a machine, or ship it with your application, copy the needed components from <ICU>\bin\ to a location on the system PATH or to your application directory.

Using MSDEV At The Command Line Note: You can build ICU from the command line. Assuming that you have properly installed Microsoft Visual C++ to support command line execution, you can run the following command, 'devenv.com <ICU>\source\allinone\allinone.sln /build "Win32|Release"'. You can also use Cygwin with this compiler to build ICU, and you can refer to the How To Build And Install On Windows with Cygwin section for more details.

Setting Active Platform Note: Even though you are able to select "x64" as the active platform, if your operating system is not a 64 bit version of Windows, the build will fail. To set the active platform, two different possibilities are:

Setting Active Configuration Note: To set the active configuration, two different possibilities are:

Batch Configuration Note: If you want to build the Win32 and x64 platforms and Debug and Release configurations at the same time, choose "Build" menu, and select "Batch Build...". Click the "Select All" button, and then click the "Rebuild" button.

How To Build And Install On Windows with Cygwin

Building International Components for Unicode with this configuration requires:

There are two ways you can build ICU with Cygwin. You can build with gcc or Microsoft Visual C++. If you use gcc, the resulting libraries and tools will depend on the Cygwin environment. If you use Microsoft Visual C++, the resulting libraries and tools do not depend on Cygwin and can be more easily distributed to other Windows computers (the generated man pages and shell scripts still need Cygwin). To build with gcc, please follow the "How To Build And Install On UNIX" instructions, while you are inside a Cygwin bash shell. To build with Microsoft Visual C++, please use the following instructions:

  1. Start the Windows "Command Prompt" window. This is different from the gcc build, which requires the Cygwin Bash command prompt. The Microsoft Visual C++ compiler will not work with a bash command prompt.
  2. If the computer isn't set up to use Visual C++ from the command line, you need to run vcvars32.bat.
    For example:
    "C:\Program Files\Microsoft Visual Studio 8\VC\bin\vcvars32.bat" can be used for 32-bit builds or
    "C:\Program Files (x86)\Microsoft Visual Studio 8\VC\bin\amd64\vcvarsamd64.bat" can be used for 64-bit builds on Windows x64.
  3. Unzip the icu-XXXX.zip file into any convenient location. Using command line zip, type "unzip -a icu-XXXX.zip -d drive:\directory", or just use WinZip.
  4. Change directory to "icu/source", which is where you unzipped ICU.
  5. Run "bash ./runConfigureICU Cygwin/MSVC" (See Windows configuration note and non-functional configure options below).
  6. Type "make" to compile the libraries and all the data files. This make command should be GNU make.
  7. Optionally, type "make check" to run the test suite, which checks for ICU's functionality integrity (See testing note below).
  8. Type "make install" to install ICU. If you used the --prefix= option on configure or runConfigureICU, ICU will be installed to the directory you specified. (See installation note below).

Configuring ICU on Windows NOTE:

Ensure that the order of the PATH is MSVC, Cygwin, and then other PATHs. The configure script needs certain tools in Cygwin (e.g. grep).

Also, you may need to run "dos2unix.exe" on all of the scripts (e.g. configure) in the top source directory of ICU. To avoid this issue, you can download the ICU source for Unix platforms (icu-xxx.tgz).

In addition to the Unix configuration note the following configure options currently do not work on Windows with Microsoft's compiler. Some options can work by manually editing icu/source/common/unicode/pwin32.h, but manually editing the files is not recommended.

How To Build And Install On UNIX

Building International Components for Unicode on UNIX requires:

Here are the steps to build ICU:

  1. Decompress the icu-X.Y.tgz (or icu-X.Y.tar.gz) file. For example, "gunzip -d < icu-X.Y.tgz | tar xvf -"
  2. Change directory to the "icu/source".
  3. Run "chmod +x runConfigureICU configure install-sh" because these files may have the wrong permissions.
  4. Run the runConfigureICU script for your platform. (See configuration note below).
  5. Type "gmake" (or "make" if GNU make is the default make on your platform) to compile the libraries and all the data files. The proper name of the GNU make command is printed at the end of the configuration run, as in "You must use gmake to compile ICU".
    Note that the compilation command output may be simplified on your platform. If this is the case, you will see just:

    gcc ... stubdata.c

    rather than

    gcc -DU_NO_DEFAULT_INCLUDE_UTF_HEADERS=1 -D_REENTRANT -I../common -DU_ATTRIBUTE_DEPRECATED= -O2 -Wall -std=c99 -pedantic -Wshadow -Wpointer-arith -Wmissing-prototypes -Wwrite-strings -c -DPIC -fPIC -o stubdata.o stubdata.c

    .
    If you need to see the whole compilation line, use "gmake VERBOSE=1". The full compilation line will print if an error occurs.
  6. Optionally, type "gmake check" to run the test suite, which checks for ICU's functionality integrity (See testing note below).
  7. Type "gmake install" to install ICU. If you used the --prefix= option on configure or runConfigureICU, ICU will be installed to the directory you specified. (See installation note below).

Configuring ICU NOTE: Type "./runConfigureICU --help" for help on how to run it and a list of supported platforms. You may also want to type "./configure --help" to print the available configure options that you may want to give runConfigureICU. If you are not using the runConfigureICU script, or your platform is not supported by the script, you may need to set your CC, CXX, CFLAGS and CXXFLAGS environment variables, and type "./configure". HP-UX users, please see this note regarding HP-UX multithreaded build issues with newer compilers. Solaris users, please see this note regarding Solaris multithreaded build issues.

ICU is built with strict compiler warnings enabled by default. If this causes excessive numbers of warnings on your platform, use the --disable-strict option to configure to reduce the warning level.

Running The Tests From The Command Line NOTE: You may have to set certain variables if you with to run test programs individually, that is apart from "gmake check". The environment variable ICU_DATA can be set to the full pathname of the data directory to indicate where the locale data files and conversion mapping tables are when you are not using the shared library (e.g. by using the .dat archive or the individual data files). The trailing "/" is required after the directory name (e.g. "$Root/source/data/out/" will work, but the value "$Root/source/data/out" is not acceptable). You do not need to set ICU_DATA if the complete shared data library is in your library path.

Installing ICU NOTE: Some platforms use package management tools to control the installation and uninstallation of files on the system, as well as the integrity of the system configuration. You may want to check if ICU can be packaged for your package management tools by looking into the "packaging" directory. (Please note that if you are using a snapshot of ICU from Subversion, it is probable that the packaging scripts or related files are not up to date with the contents of ICU at this time, so use them with caution).

How To Build And Install On z/OS (OS/390)

You can install ICU on z/OS or OS/390 (the previous name of z/OS), but IBM tests only the z/OS installation. You install ICU in a z/OS UNIX system services file system such as HFS or zFS. On this platform, it is important that you understand a few details:

z/OS (Batch/PDS) support outside the UNIX system services environment

By default, ICU builds its libraries into the UNIX file system (HFS). In addition, there is a z/OS specific environment variable (OS390BATCH) to build some libraries into the z/OS native file system. This is useful, for example, when your application is externalized via Job Control Language (JCL).

The OS390BATCH environment variable enables non-UNIX support including the batch environment. When OS390BATCH is set, the libicui18nXX.dll, libicuucXX.dll, and libicudtXXe.dll binaries are built into data sets (the native file system). Turning on OS390BATCH does not turn off the normal z/OS UNIX build. This means that the z/OS UNIX (HFS) DLLs will always be created.

Two additional environment variables indicate the names of the z/OS data sets to use. The LOADMOD environment variable identifies the name of the data set that contains the dynamic link libraries (DLLs) and the LOADEXP environment variable identifies the name of the data set that contains the side decks, which are normally the files with the .x suffix in the UNIX file system.

A data set is roughly equivalent to a UNIX or Windows file. For most kinds of data sets the operating system maintains record boundaries. UNIX and Windows files are byte streams. Two kinds of data sets are PDS and PDSE. Each data set of these two types contains a directory. It is like a UNIX directory. Each "file" is called a "member". Each member name is limited to eight bytes, normally EBCDIC.

Here is an example of some environment variables that you can set prior to building ICU:

OS390BATCH=1
LOADMOD=USER.ICU.LOAD
LOADEXP=USER.ICU.EXP

The PDS member names for the DLL file names are as follows:

IXMIXXIN --> libicui18nXX.dll
IXMIXXUC --> libicuucXX.dll
IXMIXXDA --> libicudtXXe.dll

You should point the LOADMOD environment variable at a partitioned data set extended (PDSE) and point the LOADEXP environment variable at a partitioned data set (PDS). The PDSE can be allocated with the following attributes:

Data Set Name . . . : USER.ICU.LOAD
Management class. . : **None**
Storage class . . . : BASE
Volume serial . . . : TSO007
Device type . . . . : 3390
Data class. . . . . : LOAD
Organization  . . . : PO
Record format . . . : U
Record length . . . : 0
Block size  . . . . : 32760
1st extent cylinders: 1
Secondary cylinders : 5
Data set name type  : LIBRARY

The PDS can be allocated with the following attributes:

Data Set Name . . . : USER.ICU.EXP
Management class. . : **None**
Storage class . . . : BASE
Volume serial . . . : TSO007
Device type . . . . : 3390
Data class. . . . . : **None**
Organization  . . . : PO
Record format . . . : FB
Record length . . . : 80
Block size  . . . . : 3200
1st extent cylinders: 3
Secondary cylinders : 3
Data set name type  : PDS

How To Build And Install On The IBM i Family (IBM i, i5/OS OS/400)

Before you start building ICU, ICU requires the following:

The following describes how to setup and build ICU. For background information, you should look at the UNIX build instructions.

  1. Create target library. This library will be the target for the resulting modules, programs and service programs. You will specify this library on the OUTPUTDIR environment variable. 
    CRTLIB LIB(libraryname)
ADDENVVAR ENVVAR(OUTPUTDIR) VALUE('libraryname') REPLACE(*YES)
  2. Set up the following environment variables and job characteristics in your build process 
    ADDENVVAR ENVVAR(MAKE) VALUE('gmake') REPLACE(*YES)
CHGJOB CCSID(37)
  3. Run 'QSH'
  4. Run:
    export PATH=/QIBM/ProdData/DeveloperTools/qsh/bin:$PATH:/QOpenSys/usr/bin
  5. Run gzip -d on the ICU source code compressed tar archive (icu-X.Y.tgz).
  6. Run unpax-icu.sh on the tar file generated from the previous step.
  7. Change your current directory to icu/as_is/os400.
  8. Run qsh bldiculd.sh to build the program ICULD which ICU will use for linkage.
  9. Change your current directory to icu/source.
  10. Run './runConfigureICU IBMi' (See configuration note for details). Note that --with-data-packaging=archive and setting the --prefix are recommended, building in default (dll) mode is currently not supported.
  11. Run 'gmake' to build ICU. (Do not use the -j option)
  12. Run 'gmake check QIBM_MULTI_THREADED=Y' to build and run the tests. You can look at the iSeries Information Center for more details regarding the running of multiple threads on IBM i.

How To Cross Compile ICU

This section will explain how to build ICU on one platform, but to produce binaries intended to run on another. This is commonly known as a cross compile.

Normally, in the course of a build, ICU needs to run the tools that it builds in order to generate and package data and test-data.In a cross compilation setting, ICU is built on a different system from that which it eventually runs on. An example might be, if you are building for a small/headless system (such as an embedded device), or a system where you can't easily run the ICU command line tools (any non-UNIX-like system).

To reduce confusion, we will here refer to the "A" and the "B" system.System "A" is the actual system we will be running on- the only requirements on it is are it is able to build ICU from the command line targetting itself (with configure or runConfigureICU), and secondly, that it also contain the correct toolchain for compiling and linking for the resultant platform, referred to as the "B" system.

The autoconf docs use the term "build" for A, and "host" for B. More details at: http://www.gnu.org/software/autoconf/manual/html_node/Specifying-Names.html

Three initially-empty directories will be used in this example:

/icua copy of the ICU source
/buildAan empty directory, it will contain ICU built for A
(MacOSX in this case)
/buildBan empty directory, it will contain ICU built for B
(HaikuOS in this case)
  1. Check out or unpack the ICU source code into the /icu directory.You will have the directories /icu/source, etc.
  2. Build ICU in /buildA normally (using runConfigureICU or configure): 
    cd /buildA
sh /icu/source/runConfigureICU MacOSX
gnumake
  3. Set PATH or other variables as needed, such as CPPFLAGS.
  4. Build ICU in /buildB
    Note: "--with-cross-build" takes an absolute path.
    cd /buildB
sh /icu/source/configure --host=i586-pc-haiku --with-cross-build=/buildA
gnumake
  5. Tests and testdata can be built with "gnumake tests".

How To Package ICU

There are many ways that a person can package ICU with their software products. Usually only the libraries need to be considered for packaging.

On UNIX, you should use "gmake install" to make it easier to develop and package ICU. The bin, lib and include directories are needed to develop applications that use ICU. These directories will be created relative to the "--prefix=dir" configure option (See the UNIX build instructions). When ICU is built on Windows, a similar directory structure is built.

When changes have been made to the standard ICU distribution, it is recommended that at least one of the following guidelines be followed for special packaging.

  1. Add a suffix name to the library names. This can be done with the --with-library-suffix configure option.
  2. The installation script should install the ICU libraries into the application's directory.

Following these guidelines prevents other applications that use a standard ICU distribution from conflicting with any libraries that you need. On operating systems that do not have a standard C++ ABI (name mangling) for compilers, it is recommended to do this special packaging anyway. More details on customizing ICU are available in the User's Guide. The ICU Source Code Organization section of this readme.html gives a more complete description of the libraries.

Here is an example of libraries that are frequently packaged.
Library Name Windows Filename Linux Filename Comment
Data Library icudtXYl.dll libicudata.so.XY.Z Data required by the Common and I18n libraries. There are many ways to package and customize this data, but by default this is all you need.
Common Library icuucXY.dll libicuuc.so.XY.Z Base library required by all other ICU libraries.
Internationalization (i18n) Library icuinXY.dll libicui18n.so.XY.Z A library that contains many locale based internationalization (i18n) functions.
Layout Engine iculeXY.dll libicule.so.XY.Z An optional engine for doing font layout.
Layout Extensions Engine iculxXY.dll libiculx.so.XY.Z An optional engine for doing font layout that uses parts of ICU.
ICU I/O (Unicode stdio) Library icuioXY.dll libicuio.so.XY.Z An optional library that provides a stdio like API with Unicode support.
Tool Utility Library icutuXY.dll libicutu.so.XY.Z An internal library that contains internal APIs that are only used by ICU's tools. If you do not use ICU's tools, you do not need this library.

Normally only the above ICU libraries need to be considered for packaging. The versionless symbolic links to these libraries are only needed for easier development. The X, Y and Z parts of the name are the version numbers of ICU. For example, ICU 2.0.2 would have the name libicuuc.so.20.2 for the common library. The exact format of the library names can vary between platforms due to how each platform can handles library versioning.

Important Notes About Using ICU

Using ICU in a Multithreaded Environment

Some versions of ICU require calling the u_init() function from uclean.h to ensure that ICU is initialized properly. In those ICU versions, u_init() must be called before ICU is used from multiple threads. There is no harm in calling u_init() in a single-threaded application, on a single-CPU machine, or in other cases where u_init() is not required.

In addition to ensuring thread safety, u_init() also attempts to load at least one ICU data file. Assuming that all data files are packaged together (or are in the same folder in files mode), a failure code from u_init() usually means that the data cannot be found. In this case, the data may not be installed properly, or the application may have failed to call udata_setCommonData() or u_setDataDirectory() which specify to ICU where it can find its data.

Since u_init() will load only one or two data files, it cannot guarantee that all of the data that an application needs is available. It cannot check for all data files because the set of files is customizable, and some ICU services work without loading any data at all. An application should always check for error codes when opening ICU service objects (using ucnv_open(), ucol_open(), C++ constructors, etc.).

ICU 3.4 and later

ICU 3.4 self-initializes properly for multi-threaded use. It achieves this without performance penalty by hardcoding the core Unicode properties data, at the cost of some flexibility. (For details see Jitterbug 4497.)

u_init() can be used to check for data loading. It tries to load the converter alias table (cnvalias.icu).

ICU 2.6..3.2

These ICU versions require a call to u_init() before multi-threaded use. The services that are directly affected are those that don't have a service object and need to be fast: normalization and character properties.

u_init() loads and initializes the data files for normalization and character properties (unorm.icu and uprops.icu) and can therefore also be used to check for data loading.

ICU 2.4 and earlier

ICU 2.4 and earlier versions were not prepared for multithreaded use on multi-CPU platforms where the CPUs implement weak memory coherency. These CPUs include: Power4, Power5, Alpha, Itanium. u_init() was not defined yet.

Using ICU in a Multithreaded Environment on HP-UX

When ICU is built with aCC on HP-UX, the -AA compiler flag is used. It is required in order to use the latest <iostream> API in a thread safe manner. This compiler flag affects the version of the C++ library being used. Your applications will also need to be compiled with -AA in order to use ICU.

Using ICU in a Multithreaded Environment on Solaris

Linking on Solaris

In order to avoid synchronization and threading issues, developers are suggested to strictly follow the compiling and linking guidelines for multithreaded applications, specified in the following document from Sun Microsystems. Most notably, pay strict attention to the following statements from Sun:

To use libthread, specify -lthread before -lc on the ld command line, or last on the cc command line.

To use libpthread, specify -lpthread before -lc on the ld command line, or last on the cc command line.

Failure to do this may cause spurious lock conflicts, recursive mutex failure, and deadlock.

Source: "Solaris Multithreaded Programming Guide, Compiling and Debugging", Sun Microsystems, Inc., Apr 2004
http://docs.sun.com/app/docs/doc/816-5137/6mba5vpke?a=view

Windows Platform

If you are building on the Win32 platform, it is important that you understand a few of the following build details.

DLL directories and the PATH setting

As delivered, the International Components for Unicode build as several DLLs, which are placed in the "<ICU>\bin" directory. You must add this directory to the PATH environment variable in your system, or any executables you build will not be able to access International Components for Unicode libraries. Alternatively, you can copy the DLL files into a directory already in your PATH, but we do not recommend this. You can wind up with multiple copies of the DLL and wind up using the wrong one.

Changing your PATH

Windows 2000/XP: Use the System Icon in the Control Panel. Pick the "Advanced" tab. Select the "Environment Variables..." button. Select the variable PATH in the lower box, and select the lower "Edit..." button. In the "Variable Value" box, append the string ";<ICU>\bin" to the end of the path string. If there is nothing there, just type in "<ICU>\bin". Click the Set button, then the OK button.

Note: When packaging a Windows application for distribution and installation on user systems, copies of the ICU DLLs should be included with the application, and installed for exclusive use by the application. This is the only way to insure that your application is running with the same version of ICU, built with exactly the same options, that you developed and tested with. Refer to Microsoft's guidelines on the usage of DLLs, or search for the phrase "DLL hell" on msdn.microsoft.com.

UNIX Type Platform

If you are building on a UNIX platform, and if you are installing ICU in a non-standard location, you may need to add the location of your ICU libraries to your LD_LIBRARY_PATH or LIBPATH environment variable (or the equivalent runtime library path environment variable for your system). The ICU libraries may not link or load properly without doing this.

Note that if you do not want to have to set this variable, you may instead use the --enable-rpath option at configuration time. This option will instruct the linker to always look for the libraries where they are installed. You will need to use the appropriate linker options when linking your own applications and libraries against ICU, too. Please refer to your system's linker manual for information about runtime paths. The use of rpath also means that when building a new version of ICU you should not have an older version installed in the same place as the new version's installation directory, as the older libraries will used during the build, instead of the new ones, likely leading to an incorrectly build ICU. This is the proper behavior of rpath.

Platform Dependencies

Porting To A New Platform

If you are using ICU's Makefiles to build ICU on a new platform, there are a few places where you will need to add or modify some files. If you need more help, you can always ask the icu-support mailing list. Once you have finished porting ICU to a new platform, it is recommended that you contribute your changes back to ICU via the icu-support mailing list. This will make it easier for everyone to benefit from your work.

Data For a New Platform

For some people, it may not be necessary for completely build ICU. Most of the makefiles and build targets are for tools that are used for building ICU's data, and an application's data (when an application uses ICU resource bundles for its data).

Data files can be built on a different platform when both platforms share the same endianness and the same charset family. This assertion does not include platform dependent DLLs/shared/static libraries. For details see the User Guide ICU Data chapter.

ICU 3.6 removes the requirement that ICU be completely built in the native operating environment. It adds the icupkg tool which can be run on any platform to turn binary ICU data files from any one of the three formats into any one of the other data formats. This allows a application to use ICU data built anywhere to be used for any other target platform.

WARNING! Building ICU without running the tests is not recommended. The tests verify that ICU is safe to use. It is recommended that you try to completely port and test ICU before using the libraries for your own application.

Adapting Makefiles For a New Platform

Try to follow the build steps from the UNIX build instructions. If the configure script fails, then you will need to modify some files. Here are the usual steps for porting to a new platform:

  1. Create an mh file in icu/source/config/. You can use mh-linux or a similar mh file as your base configuration.
  2. Modify icu/source/aclocal.m4 to recognize your platform's mh file.
  3. Modify icu/source/configure.in to properly set your platform C Macro define.
  4. Run autoconf in icu/source/ without any options. The autoconf tool is standard on most Linux systems.
  5. If you have any optimization options that you want to normally use, you can modify icu/source/runConfigureICU to specify those options for your platform.
  6. Build and test ICU on your platform. It is very important that you run the tests. If you don't run the tests, there is no guarentee that you have properly ported ICU.

Platform Dependent Implementations

The platform dependencies have been mostly isolated into the following files in the common library. This information can be useful if you are porting ICU to a new platform.

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