Build C/C++ Executables for android using NDK

Hello everyone,

I was wandering if I can compile C binary that runs on android platform, So a long time ago I found a method (without using ndk), with

     arm-none-linux-gnueabi-gcc -static test.c -o test

Using above command, we can compile a C file named test.c as a static binary. Yes, with this method we can only compile static binaries. But I thought hey.. that is not the most convenient way to compile means I don’t want to compile my binary every time static.

So, I found an alternative (and proper) way to build C/C++ executable using Android NDK. Let’s take an example to see how it works.

Prerequisites:

1. Linux Host (not yet tried on windows)

2. Android NDK on host machine

Let’s create a simple hello world C program in file test.c

#include <stdio.h>
#include <stdlib.h>
int main()
{
     printf("Hello World\n");
     return 0;
}

So, above program will just print “Hello World” on standard output.

Now, to compile it with NDK, we need a Android.mk. the Android.mk will look like this.

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS) 
# give module name
LOCAL_MODULE    := hello_world  
# list your C files to compile
LOCAL_SRC_FILES := test.c
# this option will build executables instead of building library for android application.
include $(BUILD_EXECUTABLE)

The NDK system is only able to compile in android project hierarchy.

So, we need to create a directory structure like this

hello_world
     |
     `-- jni
     `-- libs

Now, place test.c and Android.mk file in jni directory.

Follow these steps on command line:

     $ mkdir  ~/hello_world/
     $ mkdir ~/hello_world/jni
     $ mkdir ~/hello_world/libs
     $ cd ~/hello_world/jni/
     $ gedit test.c
               # create your C code in file, save and exit.
     $ gedit Android.mk
               # write Android.mk contents, save and exit.
     $ export PATH=$PATH:<path/to/ndk>/
     $ ndk-build

By executing “ndk-build”, ndk will compile our test.c (not static) and puts the binary in hello_world/libs/armeabi/

Advantages of using NDK:

1. We don’t have to compile binaries static, so size of binary will be reduced.

2. We can use android C/C++ libraries like liblog to print output in logcat from C.

Let me know if you have any doubts on this in comments.