December 09, 2013

Unsung Cross-Platform Hero

HTML5? Guess Again!

In most developer circles, talk of cross-platform development immediately leads to a discussion about the merits of HTML5. More specifically, javascript as the new mobile VM. As you might suspect, the world is much bigger than this. I thought I would briefly highlight another approach that is anything but trendy. Yet it can be the perfect solution in many scenarios…

One Language…

What if I told you it was possible to write most of your app once and not in javascript? What if I also told you that the secret lies in writing native code?

Native Code?

It’s a common belief that native code in Android is written in java while native code in iOS is written in Objective-C. Not so fast. A stricter definition for “native” code is really talking about the actual instructions being executed by the processor. So far, there isn’t a ubiquitous processor that understands Java. The same is true for Objective-C (although it is much closer since it’s technically compiled into native instructions). The key is finding a language that is high-level enough to be productive yet can run natively in both environments. What’s the greatest common denominator?

No Surprises

As it turns out, Objective-C is a superset of C. It may be a little-known fact, but you can actually run C code in your iOS app without any special effort. That doesn’t help us unless we could get that same C code to run on an Android device. These devices generally run with the same processors, so that isn’t a problem. Really it’s a question of how difficult it is to develop C code for Android. As it turns out, this support has been with Android from the very beginning. Now if you look closely at that link, you might notice that C++ is also supported (they’re just using the GNU compilers). Since Apple is technically using the Clang compiler, iOS apps can also take advantage of C++. So it really looks like C++ can serve as the language for cross-platform development! What’s the catch?


### Compilation By definition, native code must be compiled for every platform it runs on. So for a cross-platform situation, you would need to compile your native code for every device. Bummer.

High But Low

C++ is a great language for many things, but it is not really the best language for business logic. There needs to be a very compelling reason to leverage C++. In other words, cross-platform certainly is not enough. Here are some areas where C++ may be a good solution:

  • CPU-intensive algorithms and calculations
  • Anything pushing the limits of device I/O throughput
  • Anything that may require custom memory management
  • Anything using lots of device memory
  • Anything that does 3D graphics
  • You get the idea


Anything substantial written in C++ will certainly use libraries. And those libraries will almost certainly use other libraries. It is essential to do plenty of homework on each library in use. Is the library mobile-friendly? Will this library be compatible on the other X platforms?

In the Real World

### Dropbox Here is a video of some DropBox engineers giving an overview of their native cross-platform approach.

OpenGL Situations

Here is a link to a project that shows how to write native cross-platform code using OpenGL.


Even if C++ won’t be the first tool you choose for your cross-platform needs, it should have a special place in your toolbox. It’s easy to forget that the vast majority of all software is 1) written in C/C++ or 2) runs on a VM that is written in C/C++. Sounds like a powerful tool to have!


mobile c c++