C vs C++ performance.

C++ takes a hit on virtual functions. But it is not a disadvantage of the language, as you will get similar performance hits if you emulate virtual functions using function pointers in C.

C++ has a lot of features that can make very complex code very fast. For example, templates. C++ could also be much faster in a lot of cases as the compiler knows more about your data types, reducing the probability of pointer aliasing.

Besides this, there is very little performance difference between the languages.

From Wikipedia:

In C, any function pointer argument may alias any other function pointer argument. The compiler must assume that any accesses through these pointers can alias. This dramatically restricts the potential for optimization.

In C++, pointer arguments are assumed not to alias if they point to fundamentally different types. This allows more optimizations to be done than in C.

These aliasing optimizations may lead to big performance gains in c++ code. To get the same performance in c would require judicious use of the restrict keyword.

-Debdatta Basu.

One aspect not addressed so far, is whether it matters or not.

In modern systems, it's rare that the language is a serious factor in determining performance.

The way you structure your code, makes a bigger impact than the compiler.

Simply avoiding inefficient programming practices, can get you more mileage than worrying over the language.

In olden days, when 12mhz was a fast processor speed, the language used did matter. It was a common practice for those trying to squeeze a little more performance, to compile to assembly, just to count how many, and what kinds of instructions our code was producing, to shave off a few cycles here and there.

These days, I don't bother. Most of what I write, barely makes a mark on CPU utilization.

You'll go far if you avoid two common pitfalls...
1. Try not to pass objects by value. Use const references if you can.
2. Don't instantiate objects inside of inner loops if you don't have to.

C is a subset of C++. That's why C++ has an increment operator built into the name. It's C with stuff added.

Are you trying to say that system software is never written in C++?
The current versions of the Windows OS's are largely written in C++.

Straight C is used for system software for a number of reasons.

1. The system was written before C++ was released.
2. The system has a C compiler ported to it, but not a C++ compiler.
3. The developer prefers to write in C.
4. Someone involved in the project, believes the misconception that C is faster than C++.
5. A design decision was made to stick to C, for architectural reasons.

Further, classes on their own don't slow down the execution time by a meaningful degree. The initial overhead in using objects, is that an object pointer (this), is passed to every member function behind the scenes. This adds an implicit push to the stack on every call.

In C, you would still be making that push when you pass an argument for a target object, unless you're just dealing with globals. But you can do that in C++ with static members too... So there's nothing gained on this account.

When it comes to virtual functions, C++ does see a small performance hit, because it does a table lookup for the correct function. You commonly see this in C though, when you're using lists, maps or arrays of function pointers. But if you have too much overhead in using virtual methods for a call, you'd optimize it out in C++, just like you would in C procedure that's eating up too many cycles.

The advantages of C++ outweigh the small disadvantages of performance.
namespaces and polymorphism eliminate some major headaches in C, which are issues with naming collisions.

If you prefer C, you can still program in C using C++, and gain the advantages of these features.

I think C++ is faster than C...may be i am wrong but it seems to me that.You can read a link here over this topic..
http://unthought.net/c++/c_vs_c++.html[^]