One reason that I know of is that you can get better performance.

Now I know that there are claims that C# and Java are performance competitive with C++. You see some of that in the benchmark game at http://shootout.alioth.debian.org for simple problems a wide variety of results. One interesting one, the n-body problem, which involves a lot of hard-core computation, is the winner C++ or Java or .net? Well, http://shootout.alioth.debian.org/u32/performance.php?test=n... says that the winner is . . . Fortran!! (Not my favorite language either). g++ comes out at a factor of 1.3, the best Java at 1.5, and the best C# comes out at 2.1. That is, it takes the best C# program 2.1 times as long to compute this problem than the fastest program.

The stackexchange post said But in this era, the performance of a program written in a language based on frameworks such as C# and Java can be pretty close to that of C++ A factor of 1.6 is not pretty close, in my book. If you are in high speed markets and all other things being equal, placing your order at 1.6 ms when the other guy places it at 1.0 ms means what? It means you are further down in the order book. You lose.

So we all know that these toy benchmarks don't really represent what happens in a large, useful program. It would be interesting to build a more extensive benchmark set, don't you think?

Having worked on a very high-performance stock options feed, I can share some of my experience. The development goes something like this. You start out in C++, cause you get objects, and other useful stuff. You see that during peaks of the day, say around 0900 cst that you are beginning to fall behind. So you begin to tune.

See, lots of people decry the C++/C combination saying that they are different languages. Well, sort of. If you are on a theoretical or dogmatic bent, sure. But if you have a C++ program that is taking too long, you can relatively easily, bit-by-bit, turn it into a C program. So I am fine with the C/C++ designation in practice.

You tune this thing, making sure that you allocate your objects, say, at 0829 in the day and tend to leave them there until 1500. Then you up the -O count, hoping you are not pulling a Heisenberg. If you still need a little headroom, you learn that you can turn off exceptions in g++. Yes, even thought you don't ever throw an exception, having that not disabled costs you CPU. (What were they thinking?). So while the compile flags and the source program extension says C++, what you are executing more closely resembles C.

But there are those who fervently say that in such an environment that Java is competitive with C/C++. If you look at the cost to build the program, I am likely to agree that that part of the effort is faster with Java. But can you tune Java as much as C++? Or .net? I am suspecting not.

I think we should have a more broad-based real-life example. I am thinking that a simulated financial exchange repeatedly implemented in competing languages might be a more interesting example. In fact, I think I will go off and give that a try. Say maybe Lisp (note that it whips Java server in some examples, take that!), Java, C++ and certainly not Fortran (due to personal prejudices).

I'll let you know how that turns out.