Introduction Using C functions from C++ is very easy but going the other way isn’t. However, it can be done with a little ingenuity. Really, this isn’t as crazy as it sounds. I’ll use a simple adder for the object. It takes an integer as a starting value and has two functions for adding and getting the current value. This could be expanded later into a complex object for mathematical operations but that’s really not necessary right now....
Introduction So far we’ve scratched the surface of using JNI when we looked at wrapping a C library and Calling Java from C. Now we’re going to look into some more complex uses. Java Class Since we’re working with JNI, we’ll need a Java class to use what we’re going to expose from C. DemoFuncs.java class DemoFuncs { static { System.loadLibrary("demo_lib"); } public enum Days { MON, TUE, WED, THU, FRI, SAT, SUN, } public static native int[] demo_array_return(); public static native int[] demo_array_copy_inc(int[] in); public static native Days demo_enum_val(); public static native Days demo_enum_field_val(); public static native void demo_exception_1(); public static native void demo_exception_2(); public static native void demo_exception_3(); public static native boolean demo_exception_4(); public static native Name demo_name(String name); } Note: This class includes an enum because one of the later examples uses them....
Introduction Obviously, JNI lets you call Java functions and use Java classes in C. Typical a Java app is the one calling into C. Now Let’s say you don’t have a Java app that kicks off the process but you want your C app to still use some Java code. Okay, I know what you’re thinking, “why”? Well, there are companies out there that provide SDKs for their products only in Java....
Introduction It can’t be argued that Java is popular and successful. It is consistently the number one language on TIOBE’s popularity list, above C which comes in as number two. This ranking is based on popularity and doesn’t mean Java is more used than C but that doesn’t change the fact that there is a lot of Java code out there. Unlike other languages interop with Java is not what I’d call easy....
Introduction Using C functions from Objective-C is very easy but going the other way isn’t so easy. Especially with ARC which can destroy the object out from under you because C code is outside of ARC. With ARC Objective-C objects are no longer allowed in C structs for this very reason. Here is a situation I ran into where I needed to use Objective-C objects from within C. At work we have a library that was ported to iOS....