Thread: Class in C

Hi all, I am not sure with C about one thing, I know that C is not an Object-oriented language.
so it means we cannot implement any class by using C?

Classes aren't supported by C. If you want them, you'll have to use C++.
(But structs are supported.)

C doesn't have classes. It has the simple precursor to classes -- structs.
In C, a struct can only have data (no functions), although you can have pointers to functions. It therefore has no constructors & destructors... Also, the data in a struct is all public. It's mostly just a container to hold multiple data variables in one package.

You CAN use objects in C with Objective-C.

Objective-C (or objc as it is sometimes written) is a superset of C. This means that it IS C, but with objects added. You don't even have to use objects in objc, you a totally free to choose when to use a procedural C approach to a problem or when to change to an object orientate approach.

In objective-C you always refer to an object by a pointer. For example, if I had a 'Person' object, you would send methods to it like this,

Code:

Person *myPersonObject = [Person new];
[myPersonObject setName:"twonk"];
const char* personName = [myPersonObject name];

In objc the square brackets are used only when the contents are objects (pointer to objects) and methods, i.e.

<result> = [<object> <method>].

If the method takes arguments, then they come after an colon, i.e.

<result> = [<object> <method with parameters>:<parameter>].

In the above example, I made a new Person object by sending the class 'Person' the 'new' method. I then set the name of the object to "twonk" by using a C string as a parameter, I then asked person object for its instance variables 'name' (which I just set).

The code to define objects in objc looks like this,

Code:

// all for this goes in a file called Person.h
#import <object.h>

@interface Person : Object
{
    const char *name;
}

- (const char*) name;


@end

This is the 'class interface'. The instance variables are defined separately from the methods. The instance variables are defined in the curly brackets, the methods defined afterwards. Instance methods follow the pattern,

- (<return type>) <method name>;

The hyphen indicates the start of the method, followed by the return type (e.g. float, double, or even another object) in parentheses, finally we have the method name and end with a semicolon.

Next we define the 'class implementation',

Code:

//all of this goes in a file called Person.m  the .m indicated an ObjC file.
#import "Person.h"

@implementation Person

- (const char*) name 
{
    return name;
}

@end

The implementation is very similar to the interface apart from it a bit simpler. We get rid of the semicolon and add curly brackets to the method name.

A good introduction to the topic is here, http://www.otierney.net/objective-c.html

And don't forget, the native MacOS programming language is objc. You use iTunes, it's built with (at least in part) Objective-C. Objective-C lies at the heart of the iPhone and iPod Touch's interfaces. The first web browser was built using objective-c. Doom was coded in Objective-C ... it's a good language ;o)

Err, struct is almost a class. I can't see how. Classes are (can be) indefinitely much more complex than structs with virtual functions, public, protected, private, etc.
C++ classes can be used for so much more than a C struct. Polymorphism, for example.
I don't think I agree with that statement at all.

Yes I'm referring to a C++ struct. In pure C using any C++ reserved keywords will cause the compiler to barf.

Originally Posted by boyfarrell

You CAN use objects in C with Objective-C.
...

Well I know absolutely nothing about Objective C, but is there anything in Objective C that can't be done as well or better in C++?

Originally Posted by cpjust

Well I know absolutely nothing about Objective C, but is there anything in Objective C that can't be done as well or better in C++?

I doubt it. It seems just to lack functionality that C++ has (like virtual functions), instead of adding to it. It's kinda like C+ it seems.

Originally Posted by MacGyver

C++ classes and specifics are done using under-the-hood C techniques. Function pointers and such. Nothing too fancy. Nothing brand new. Just more work underneath so we can do more for less on top.

The only class functionality I haven't found a way to duplicate in C are constructors & destructors. You can add function pointers to them, but they won't get called unless you explicitly call them.

Originally Posted by boyfarrell

I don't know anything about C++ so I can't answer that question, have a look here, C++ and Objective-C Compared.

I've never used or seen Smalltalk, but I found this quote pretty funny:

C++ has tons of features not found in Objective-C. Objective-C is a simpler language. Objective-C tries to blend the purity of Smalltalk with the simplicity of C. However, some people have said that Objective-C blends the lack of readability of C with the limitations of Smalltalk.