Can you write object-oriented code in C? [closed]

Question

Can you write object-oriented code in C? Especially with regard to polymorphism.

---

See also Stack Overflow question Object-orientation in C.

Answer 1

Yes. In fact Axel Schreiner provides his book "Object-oriented Programming in ANSI-C" for free which covers the subject quite thoroughly.

Answer 2

I believe that besides being useful in its own right, implementing OOP in C is an excellent way to learn OOP and understand its inner workings. Experience of many programmers has shown that to use a technique efficiently and confidently, a programmer must understand how the underlying concepts are ultimately implemented. Emulating classes, inheritance, and polymorphism in C teaches just this.

To answer the original question, here are a couple resources that teach how to do OOP in C:

EmbeddedGurus.com blog post "Object-based programming in C" shows how to implement classes and single inheritance in portable C: http://embeddedgurus.com/state-space/2008/01/object-based-programming-in-c/

Application Note ""C+"—Object Oriented Programming in C" shows how to implement classes, single inheritance, and late binding (polymorphism) in C using preprocessor macros: http://www.state-machine.com/resources/cplus_3.0_manual.pdf, the example code is available from http://www.state-machine.com/resources/cplus_3.0.zip

Answer 3

I've been digging this for one year:

As the GObject system is hard to use with pure C, I tried to write some nice macros to ease the OO style with C.

#include "OOStd.h"

CLASS(Animal) {
    char *name;
    STATIC(Animal);
    vFn talk;
};
static int Animal_load(Animal *THIS,void *name) {
    THIS->name = name;
    return 0;
}
ASM(Animal, Animal_load, NULL, NULL, NULL)

CLASS_EX(Cat,Animal) {
    STATIC_EX(Cat, Animal);
};
static void Meow(Animal *THIS){
    printf("Meow!My name is %s!\n", THIS->name);
}

static int Cat_loadSt(StAnimal *THIS, void *PARAM){
    THIS->talk = (void *)Meow;
    return 0;
}
ASM_EX(Cat,Animal, NULL, NULL, Cat_loadSt, NULL)


CLASS_EX(Dog,Animal){
    STATIC_EX(Dog, Animal);
};

static void Woof(Animal *THIS){
    printf("Woof!My name is %s!\n", THIS->name);
}

static int Dog_loadSt(StAnimal *THIS, void *PARAM) {
    THIS->talk = (void *)Woof;
    return 0;
}
ASM_EX(Dog, Animal, NULL, NULL, Dog_loadSt, NULL)

int main(){
    Animal *animals[4000];
    StAnimal *f;
    int i = 0;
    for (i=0; i<4000; i++)
    {
        if(i%2==0)
            animals[i] = NEW(Dog,"Jack");
        else
            animals[i] = NEW(Cat,"Lily");
    };
    f = ST(animals[0]);
    for(i=0; i<4000; ++i) {
        f->talk(animals[i]);
    }
    for (i=0; i<4000; ++i) {
        DELETE0(animals[i]);
    }
    return 0;
}

Here is my project site (I don't have enough time to write en. doc,however the doc in chinese is much better).

OOC-GCC

Answer 4

There is an example of inheritance using C in Jim Larson's 1996 talk given at the Section 312 Programming Lunchtime Seminar here: High and Low-Level C.

Answer 5

The answer to the question is 'Yes, you can'.

Object-oriented C (OOC) kit is for those who want to program in an object-oriented manner, but sticks on the good old C as well. OOC implements classes, single and multiple inheritance, exception handling.

Features

• Uses only C macros and functions, no language extensions required! (ANSI-C)

• Easy-to-read source code for your application. Care was taken to make things as simple as possible.

• Single inheritance of classes

• Multiple inheritance by interfaces and mixins (since version 1.3)

• Implementing exceptions (in pure C!)

• Virtual functions for classes

• External tool for easy class implementation

For more details, visit http://ooc-coding.sourceforge.net/.

Answer 6

I've seen it done. I wouldn't recommend it. C++ originally started this way as a preprocessor that produced C code as an intermediate step.

Essentially what you end up doing is create a dispatch table for all of your methods where you store your function references. Deriving a class would entail copying this dispatch table and replacing the entries that you wanted to override, with your new "methods" having to call the original method if it wants to invoke the base method. Eventually, you end up rewriting C++.