unicode support in android ndk

Question

I have a large C/C++ library that I need to use as part of an Android NDK project. This library needs to be able to intelligently process UTF8 strings (for example, conversion to lowercase/uppercase).

The library has conditional compilation to punt to an OS API to do the conversion, but there don't seem to be any Android APIs for UTF8. (mbstowcs, etc)

This thread says to use JNI methods to do it (!), which is a rather heavy-weight solution.

I was thinking about building ICU, but as it uses GNU Autotools I'm not sure I can make it work with the NDK toolchain. :/

Has anyone else confronted this problem and done something other than use JNI?

EDIT: My attempts to get ICU to compile fail at the configure step:

checking wchar.h usability... no
checking wchar.h presence... yes
configure: WARNING: wchar.h: present but cannot be compiled
configure: WARNING: wchar.h:     check for missing prerequisite headers?
configure: WARNING: wchar.h: see the Autoconf documentation
configure: WARNING: wchar.h:     section "Present But Cannot Be Compiled"
configure: WARNING: wchar.h: proceeding with the preprocessor's result
configure: WARNING: wchar.h: in the future, the compiler will take precedence
checking for wchar.h... yes
checking for library containing wcscpy... none required
checking size of wchar_t... 0
configure: error: There is wchar.h but the size of wchar_t is 0

Answer 1

We are using ICU in the NDK. Follow the steps in the ICU cross building instructions and you'll be OK. Basically you'll have a ICU native directory (for example Windows or Linux), a ICU Cygwin (if using such) and yet another for ICU Android (ARM). Sounds crazy, but it works!

Here are the steps for building under Cygwin. I am using the 'CrystaX' NDK r4, but it should build with the out of the box NDK as well. ICU version 4.4, but has worked with previous versions as well.

1. Patches:

   • source/configure (http://pastebin.com/kDEbYdMe)
   • source/Makefile.in (http://pastebin.com/785Lnsb5)
   • source/config/ (copy mh-linux to mh-unknown)
   • source/tools/pkgdata/pkgdata.cpp (http://pastebin.com/ZiRexjkp)

2. Build your host version of ICU (e.g. Windows) as per normal. (We'll call this $HOST_ICU)

3. Build Cygwin ICU:

   • Create a icu-cygwin directory (We'll call this $ICU_CROSS_BUILD)
   • From icu-cygwin dir, run '$HOST_ICU/source/runConfigureICU Cygwin'
   • make

4. Build NDK version of ICU:

   • Create a icu-android directory
   • From icu-android dir: '$HOST_ICU/source/configure' with appropriate command line options. --with-cross-build=$ICU_CROSS_BUILD and --host=arm-eabi is required.
   • make

I use something like this for passed in (to step #4) CPPFLAGS/CXXFLAGS/CFLAGS:

-I$NDK_ROOT/build/platforms/android-8/arch-arm/usr/include/ -O3 -fno-short-wchar -DU_USING_ICU_NAMESPACE=0 -DU_GNUC_UTF16_STRING=0 -fno-short-enums -nostdlib

And for LDFLAGS:

-lc -Wl,-rpath-link=$NDK_ROOT/build/platforms/android-8/arch-arm/usr/lib/ -L$NDK_ROOT/build/platforms/android-8/arch-arm/usr/lib/

And additional configure params:

--enable-extras=no --enable-strict=no --enable-static --enable-shared=no --enable-tests=no --enable-samples=no --enable-dyload=no --enable-tools=no --host=arm-eabi --with-data-packaging=archive

I haven't done this manually for a while, it's currently all in a custom Python based build script. If you run into any other troubles, I can probably tell you what the issue is.

Good luck!