Using C++ in an embedded environment

Question

Today I got into a very interesting conversation with a coworker, of which one subject got me thinking and googling this evening. Using C++ (as opposed to C) in an embedded

Answer 1

Now a days it will all boil down to the C++ runtime support of the platform. You're likely to find a way to compile C++ code down to almost any embedded platform with GCC, but if you can't find a suitable C++ runtime for the platform your efforts will be futile, unless you write your own C++ runtime.

Answer 2

C++ is suitable for microcontrollers and devices without an OS. You just have to know the architecture of the system and be conscious of time and space constrains, especially when doing mission critical programming.

With C++ you can do abstraction which often leads to an increased footprint in the code. You do not want this when programming for a resource-limited machine such as an 8-bit MCU.

Generally, avoid:

• Dynamic memory allocation because it represents uncertainty in timing
• Overloading
• RTTI because the memory cost is large
• Exceptions because of the execution speed lowering

Be cautious with virtual functions as they have a resource cost of a vtable per class and one pointer to the vtable per object. Also, use const in place of #define.

As you move up to 16 and 32-bit MCUs, with 10s or 100s of MB RAM, heavier features like the ones mentioned above may be used.

So to round up, C++ is useful for embedded systems. A main benefit is that OOP can be useful when you want to abstract aspects of the microcontroller, for example UART or state machines. But you may want to avoid certain features all of the time and some of the features some of the time, depending on the target you are programming for.

Answer 3

One of the few things I tend to agree with Linus is his opinion about C++ http://thread.gmane.org/gmane.comp.version-control.git/57643/focus=57918

Besides this, if you really really want to use C++ you might want to have a look at http://www.caravan.net/ec2plus/ which describes Embedded C++, or better to say you should not use in C++ for embedded systems.

Answer 4

I don't know about "general consensus", only the company I work for (which does a lot of development for mobile phones, car navigation systems, DPFs, etc.).

The main drawback I've encountered to using C++ on embedded platforms as opposed to C is that it isn't quite as portable - there are many more cases of compilers that don't adhere to the standard which can cause problems if you need to build your code with more than 1 compiler or outright have bugs in the implementation. Then there are environments where C++ code simply won't run - BREW's issues with relocatable code and its "native OOP" don't play so well with "regular" C++ classes and inheritance.

In the end, though, if you're only targeting 1 platform, I'd say use whatever you think is "better" (faster, less bugs, better design) for your development - in most cases the issues can be worked around quite easily.

Answer 5

Depends what kind of embedded development you are doing. I've done embedded development with both C++, C, and Assembly on various platforms, you can even use Java to write applications on smart phones.

For instance on a smart phone like device that's running Windows CE 5, almost all of the code is C++, including in the operating system. Only small bits are written in C or assembly.

On the other hand I've written code for an MSP430 microcontroller, which was in C, and I probably would have done that in C++ had the compiler been more reliable and standards compliant.

Also I seem to recall a university lecturer of mine talking about writing embedded code in Forth or something. So really any language can do.

Answer 6

I am currently fighting a problem with exceptions in an embedded Linux application. We are trying to port software written for a different platform that seemed to support exceptions well, but the new compiler tools (a port of gcc) reports errors when creating the eh_frame. I was against using exceptions for this tool, but the developer reassured me that modern compilers would support it well.

My opinion is that there are some advantages to C++, but I would stay away from exceptions and the standard template library. We haven't had problems using virtual functions.