Compiling against C++ standard libraries on the android toolchain

Question

I have a really simple helloworld.cpp program

#include <iostream>
using namespace std;
int main ()
{
  cout << "Hello World!";
  return 0;
}

And I'm trying to compile it for android x86 with the cross-compiler from the toolchain:

/Users/me/android-ndk-r8/toolchains/x86-4.4.3/prebuilt/darwin-x86/bin/i686-android-linux-g++ helloworld.cpp -L "/Users/me/android-ndk-r8/sources/cxx-stl/stlport/libs/x86/" -lstlport_static

However, I get errors:

helloworld.cpp:2:20: error: iostream: No such file or directory

Any idea why?

Answer 1

Check the documentation.html file included with the NDK, under "Standalone Toolchain". It says that if you invoke the compiler in this way you won't be able to "use any C++ STL". However it is possible, as the documentation explains, if you first create a "customized" toolchain installation, using something like the following command:

$NDK/build/tools/make-standalone-toolchain.sh --platform=android-8 --install-dir=/tmp/my-android-toolchain --arch=x86

where $NDK is the path to your NDK directory. Note the --arch=x86 which means that the toolchain is prepared specifically for the x86 Android. This prepares what you need in one directory, including the STL headers and folders. You should then be able to use -lstdc++ to link against the STL (static version), ie something like:

/tmp/my-android-toolchain/bin/i686-android-linux-g++ helloworld.cpp -lstdc++

For a more complete explanation, please see the NDK documentation.

Answer 2

The NDK documentation is not entirely accurate, at least not currently. In fact, it states when using the prebuilt toolchain "You won't be able to use any C++ STL (either STLport or the GNU libstdc++) with it.", but this is out of date. I created a small hello world program using the include with the same error. It can be solved without creating your own toolchain though, which is nice if you don't want to have to add one more step to your configuration process and allows you to always use the latest SDK platform without creating a new toolchain every time.

The NDK ships with the source code for several versions of standard C++ libraries: GAbi++, STLport, and GNU STL. Each flavor comes with prebuilt shared and static libs as well. My example below will use stlport.

To use the stand-alone toolchain at its installed location, you can do something like this: export CXX='$NDK_ROOT/toolchains/arm-linux-androideabi-4.8/prebuilt/darwin-x86_64/bin/arm-linux-androideabi-g++ --sysroot="$NDK_ROOT/platforms/android-19/arch-arm"'

This, for example, would set your CXX compiler to compile ARM on the OS X system using SDK platform level 19. This much you probably already knew. Also, you would want to export your CC, CPP, LD, AR, and RANLIB if you use it. I also personally create an envar for READELF.

To add support for C++ libs, you could do something like follows: $CXX helloworld.cpp -I$NDK_ROOT/sources/cxx-stl/stlport/stlport -L$NDK_ROOT/sources/cxx-stl/stlport/libs/armeabi -lstlport_shared

Note that this will link the libstlport_shared.so which will now be required at runtime, so you may need to add a relative path to the command above to support that, depending on your APK structure. If you want to just test this simple case, you can just run this on the emulator as follows:

adb push a.out /data
adb push $NDK_ROOT/sources/cxx-stl/stlport/libs/armeabi/libstlport_shared.so /data
adb shell
# su
# cd /data
# chmod 777 a.out
# ./a.out

To get rid of the headache of dealing with shared library paths, you can also statically link the C++ library in by changing "-lstlport_shared" to "-lstlport_static". There are some consequences of doing this, as explained in the NDK Dev Guide. The biggest issue is due to having the static library linked in multiple places, causing: - memory allocated in one library, and freed in the other would leak or even corrupt the heap. - exceptions raised in libfoo.so cannot be caught in libbar.so (and may simply crash the program). - the buffering of std::cout not working properly

A useful tool is also included to see what dependencies your program has, the readelf tool.

To see what other shared libraries your program requires, you can run the following: $NDK_ROOT/toolchains/arm-linux-androideabi-4.8/prebuilt/darwin-x86_64/bin/arm-linux-androideabi-readelf -a a.out | grep NEEDED

Other cool standard tools: addr2line - convert a stack trace address to a line of code nm - Displays the symbol table objdump - displays info on an object