计划效率

Question

我想知道，与任何编程语言中的结构化编程方法相比，采用面向对象的方法来解决问题是否会对程序效率产生影响，特别是在c ++中。

Answer 1

Maybe. Maybe not.

You can write efficient object-oriented code. You can write inefficient structured code.

It depends on the application, how well the code is written, and how heavily the code is optimized. In general, you should write code so that it has a good, clean, modular architecture and is well designed, then if you have problems with performance optimize the hot spots that are causing performance issues.

Use object oriented programming where it makes sense to use it and use structured programming where it makes sense to use it. You don't have to choose between one and the other: you can use both.

Answer 2

I remember back in the early 1990's when C++ was young there were studies done about this. If I remember correctly, the guys who took (well written) C++ programs and recoded them in C got around a 15% increase in speed. The guys who took C programs and recoded them in C++, and modified the imperative style of C to an OO style (but same algorithms) for C++ got the same or better performance. The apparent contradiction was explained by the observation that the C programs, in being translated to an object oriented style, became better organized. Things that you did in C because it was too much code and trouble to do better could more easily be done properly in C++.

Thinking back about this I wonder about the conclusion some. Writing a program a second time will always result in a better program, so it didn't have to be imperative to OO style that made the difference. Todays computer architectures are designed with hardware support for common operations done by OO programs, and compilers have gotten better at using the instructions, so I think that it is likely that whatever overhead a virtual function call had in 1992 it is far smaller today.

Answer 3

There doesn't have to be, if you are very careful to avoid it. If you just take the most straightforward approach, using dynamic allocation, virtual functions, and (especially) passing objects by value, then yes there will be inefficiency.

Answer 4

It doesn't have to be. Algorithm is all matters. I agree encapsulation will slow you down little bit, but compilers are there to optimize.

Answer 5

You would say no if this is the question in computer science paper.

However in the real development environment this tends to be true if the OOP paradigm is used correctly. The reason is that in real development process, we generally need to maintain our code base and that the time when OOP paradigm could help us. One strong point of OOP over structured programming like C is that in OOP it is easier to make the code maintainable. When the code is more maintainable, it means less bug and less time to fix bug and less time needed for implementing new features. The bottom line is then we will have more time to focus on the efficiency of the application.

Answer 6

The problem is not technical, it is psychological. It is in what it encourages you to do by making it easy.

To make a mundane analogy, it is like a credit card. It is much more efficient than writing checks or using cash. If that is so, why do people get in so much trouble with credit cards? Because they are so easy to use that they abuse them . It takes great discipline not to over-use a good thing.

The way OO gets abused is by

• Creating too many "layers of abstraction"

• Creating too much redundant data structure

• Encouraging the use of notification-style code, attempting to maintain consistency within redundant data structures.

It is better to minimize data structure, and if it must be redundant, be able to tolerate temporary inconsistency.

ADDED: As an illustration of the kind of thing that OO encourages, here's what I see sometimes in performance tuning: Somebody sets SomeProperty = true; . That sounds innocent enough, right? Well that can ripple to objects that contain that object, often through polymorphism that's hard to trace. That can mean that some list or dictionary somewhere needs to have things added to it or removed from it. That can mean that some tree or list control needs controls added or removed or shuffled. That can mean windows are being created or destroyed. It can also mean some things need to be changed in a database, which might not be local so there's some I/O or mutex locking to be done.

It can really get crazy. But who cares? It's abstract .

Answer 7

There could be: the OO approach tends to be closer to a decoupled approach where different modules don't go poking around inside each other. They are restricted to public interfaces, and there is always a potential cost in that. For example, calling a getter instead of just directly examining a variable; or calling a virtual function by default because the type of an object isn't sufficiently obvious for a direct call.

That said, there are several factors that diminish this as a useful observation.

1. A well written structured program should have the same modularity (ie hiding implementations), and therefore incur the same costs of indirection. The cost of calling a function pointer in C is probably going to be very similar to the cost of calling a virtual function in C++.

2. Modern JITs, and even the use of inline methods in C++, can remove the indirection cost.

3. The costs themselves are probably relatively small (typically just a few extra simple operations per instruction call). This will be insignificant in a program where the real work is done in tight loops.

4. Finally, a more modular style frees the programmer to tackle more complicated, but hopefully less complex algorithms without the peril of low level bugs.