C why use classes

Permission labels refer to the permission that the members acquire. If the permission label is not specified or declared by default, it is set to private.

They can be any of the following keywords: Private - They can be accessed by members of the same class or their friend class.

Public - Members can be accessed anywhere the class is visible. Protected - Members can be accessed by members of their same class, friend class, and derived classes. On the next page, give the project a title. In this case, we are going to name it after our class person example. Keep the default settings. It is because the compiler needs to know the definition of the code of the functionalities which is defined in the header file. If this namespace is not used, the compiler generates errors.

Go ahead and clear the default main function program example. Add the following code after using namespace std to create the class:. You need data and functions that manipulate the data. We can define functions either within the class inline member functions or outside the class non-inline member functions. This argument is typically named this. When we add an instance method abs for calculating the absolute value of a complex number we get:. Class methods must be initialized in the same way as instance methods, but have no restriction on the prototype.

A base class must be represented as a member variable with the same name and type as the base class itself. A subclass may override the base class instance method pointers to provide polymorphism.

The subclass must override with an identically prototyped function and set the base class' method pointer in the constructor after the baseclass' constructor has been called. Whenever an overriden instance method is called, we are guaranteed that it was called by an instance of the baseclass. Since the instance method receives a pointer to the base class as its first argument, we may get the subclass using the offsetof macro from stddef.

In object oriented languages each member has an access attribute and the compiler will enforce that access attribute. With Classes in C we should use comments to specify the access attributes.

For instance we use the following notation:. In object oriented languages we can specify an abstract class to guarantee that the class cannot be instanciated. Abstract methods and interfaces can be used to guarantee that subclasses override methods. It always seems like a good idea at the time but afterwards it becomes a maintenance nightmare. Your code become littered with pieces of code tying everything together. A new programmer will have lots of problems reading and understanding the code if you use function pointers since it will not be obvious what functions is called.

I have seen multiple attempts at this in the embedded environment and in the end it is always a maintenance problem. I have read through the source code of GTK and it is pretty impressive, and definitely easier to read.

The basic concept is that each "class" is simply a struct, and associated static functions. The static functions all accept the "instance" struct as a parameter, do whatever then need, and return results if necessary.

The function would simply dig through the struct, extract the position numbers, probably build a new PositionStruct object, stick the x and y in the new PositionStruct, and return it. GTK even implements inheritance this way by embedding structs inside structs. My approach would be to move the struct and all primarily-associated functions to a separate source file s so that it can be used "portably".

Depending on your compiler, you might be able to include functions into the struct , but that's a very compiler-specific extension, and has nothing to do with the last version of the standard I routinely used :. So it's very possible to have classes in C. If not then you just define a set of function pointers in the struct itself. If you want to have virtual methods it gets more complicated.

Basically you will need to implement your own VTable to each struct and assign function pointers to the VTable depending on which function is called. You would then need a set of function pointers in the struct itself that in turn call the function pointer in the VTable.

TBH though I've used it many a time and it works is fast and doesn't have memory problems. Sure you have to be a bit more careful about what you do but its really not that complicated. C isn't an OOP language, as your rightly point out, so there's no built-in way to write a true class.

You're best bet is to look at structs , and function pointers , these will let you build an approximation of a class. However, as C is procedural you might want to consider writing more C-like code i. How are we doing? Please help us improve Stack Overflow. Take our short survey. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How do you implement a class in C? Asked 12 years, 2 months ago. Active 3 years ago. Viewed k times. Improve this question. Ben Gartner Ben Gartner 13k 10 10 gold badges 35 35 silver badges 34 34 bronze badges.

Obligatory question: Do you have to write object-oriented code? If you do for whatever reason, that's fine, but you will be fighting a rather uphill battle. It's probably for the best if you avoid trying to write object-oriented code in C. Say for example we needed to control this LED both in main. In the past typically what I would have done would be just to create the implementation in a. My question is, is there any benefit for a module like this to be contained within a class?

There will only ever be one LED. I can see where this might be useful if there were multiple LEDs and the constructor took a parameter of which output they were connected to D1, D2 etc. My last question is, if there is benefit, how should main. Should they both include a constructor for the LEDControl class? Or should the LEDControl object only be created once in main. Your proposed class has no data members, that is, it is just a bag of related functions. Imagine a different class that had say increment and decrement methods and so the class needed to remember the current brightness level.

Object lifetime is an entire subject on which books could be written. In small embedded processors like Particle, the best practice is to statically allocate whenever possible so that heap fragmentation does not occur.

This leads to some slightly painful ways of working with globals, but that pain really derives from the way that memory management on the platform has to inform design. I think of it this way: we only really have two tools for organizing things—abstraction and hierarchy.