Porting C based linux application to the Android platform

Question

I have C Linux based application and now I want to port it to Android. I figured out, that I can extract the toolchain from Android NDK and build my application, but how to make the APK such that I can install it on the android devices without the need of root access.

In Linux, I used to install it using a bash script which used to put my application related files in different folders like /opt, /etc (files shared with other applications) and /var . How can we handle this in Android. Is there a folder similar to /etc in Android where I can put files that other applications can read.

Thanks
-M

Answer 1

First of all, you are lucky if your project compiles "as is" with NDK standalone toolchain. Often, bionic is not enough, and people need to tweak the build environment (from libpthread to full-blown buildroot alternate toolchain with static C runtime).

As for the shared files location, on Android it's named "external storage". Your app and other app may require special permissions to write and read to this location. Directory /opt does not exist here. You don't have write access to /etc, but files like /etc/hosts are available for read.

Regarding the APK. You are right, this is the ultimate way to distribute and install apps on Android. But you can, even without root, to locally install and run a command-line executable. Usually it's done with Developers Options turned on, and enabled USB debugging. Now you can open an adb shell, install and run your program. The trick is that external storage (see above) is marked as 'non-executable'. Therefore, you must find another place for your binary. Usually, /data/local/tmp will be a good choice.

Instead of adb, you can use a terminal emulator on the device.

If you choose to build an APK, you will probably prefer to convert your app to shared library that will perform actions for Java via JNI. But it is also possible to package your command-line binary as part of the APK and use Java Runtime.exec().