我可以在C程序中使用面向对象的头文件吗

Question

I am familiar in programming with C++ and its Object Oriented nature. Now I am supposed to work in C these days. I still want to use the header files I have already prepared in past which are Object Oriented(use class, constructor, destructor etc.). Please help me knowing about the hidden facts while doing this. Although the program doesn't give syntax erro

Answer 1

It is possible to use C for object-oriented programming. I do this. But the C language does not help you.

I will discuss using C for object-oriented programming. But please understand I am talking about practices, not about anything built into the language.

In C++, you can declare a class , and it can have public , private , and protected parts. In C, you can declare a struct , and everything in the struct will be public. In C++, a class can have associated functions; in C, functions are global. (In C, functions and variables declared static will be private to a single source file, but global within that file. Functions and variables not declared static are global through the whole program. There is no way to declare members of a struct to be private, although you are free to use a naming convention that makes it clear that some member variable are intended to be private.)

In C++, you have name spaces, and a class forms a name space. In C, there is only one global name space.

In C++, there is operator overloading; not in C.

In C++, when you declare functions as member functions, the compiler will magically make a this pointer available. In C, you can make member functions but you must explicitly give them an argument equivalent to a this pointer.

In C++, the compiler will arrange to all your constructor and destructor for you. In C, you must explicitly call your functions.

So, then, here is how to do object-oriented programming in C:

First, declare a struct to hold the data in your object. I recommend using a typedef so you can refer to it conveniently. Let's imagine you are writing a physics simulator for automobiles; let's say your struct will be typedef ed as type CAR .

Now you write a constructor and destructor function. Since the compiler doesn't help youit is worthwhile to make the effort to do it., you can't use a ~ in the name of the destructor. We will imagine your functions are declared as CAR *PcarNew(); and void FreePcar(CAR *pcar); .

Now you write member functions. A function to start the engine of the car might be void StartEnginePcar(CAR *pcar); . (If you also have trucks, you might have a void StartEnginePtruck(TRUCK *ptruck); ; if you also have buses, you might have void StartEnginePbus(BUS *pbus); ; and so on. There is only one global namespace.) As there is no this pointer, the first argument is an explicit reference to an instance of the class (ie a pointer allocated by calling the constructor).

Note that in C++ you could have an object named c that was an instance of class car and you could say c.start_engine() ; the C++ compiler knows you mean the start_engine() member function from class car . You can have any number of functions in C++ with the same name, each a member of a different class, and C++ will use name spaces to keep track of them. In C you don't get anything like that, and every function name must be unique. This is why function names in C object-oriented programming usually have the name of the "class" in the function name itself, as in StartEnginePcar() . (Some people would likely just use StartEngineCar() or CarStartEngine() but I use a particular coding style that encourages the style I used in my first examples. Use whatever coding style you like, of course.)

(As noted in a comment below, in C you can put a function pointer inside a struct and call it with the -> operator, but this is best used for cases where you don't know in advance what the function will be, not to try to duplicate some object-oriented syntax. If you need to do something like a virtual pointer in C++, you would use a function pointer in your "class" struct .)

Object-oriented programming is definitely not as nice in C as in C++, but I do think that explicitly following the OOP model in C can help your programs be easier to design and to understand.

Answer 2

C is not an Object Oriented Language.

C is an imperative ( procedural ) systems implementation language.

Assuming you have gcc compiler, try to compile with this options:

gcc -std=c99 replacewithyoursourcefilename.c -o execProgram

And you will see the compiler errors.

Is it an option to rewrite your C++ code to pure C?

I recommend you to check the C tag of StackOverflow to learn more about the language.

Hope it helps!

Answer 3

No! C standard was written before C++ standards and therefore all newer constructs give syntax errors in C. You can encapsulate C++ related things with

#ifdef __cplusplus 
..
#endif

To hide them from C compiler if this helps you to cope with compatibility issues.

Answer 4

I still want to use the header files I have already prepared in past which are Object Oriented(use class, constructor, destructor etc.)

So your header files are written in C++, making use of classes, which is C++-only syntax not available in C. So the answer ist "No, you cannot use C++ classes in C".

What you can do is either

• try to encapsulate your C++ code in a library, wrap it with an API written in C. That will only work when you have a C++ compiler available on the platform you are working, but I guess you have not (why else would you bother with C in that case?)
• rewrite your C++ classes in C, keeping an object oriented style with the C language elements. Here is a complete online book how to do object oriented programming with C.

Answer 5

您可以在StackOverflow中搜索“ c和c ++混合”以找到解决方案。