C Oop?

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June 28th, 2006, 06:23 PM

Spechal

Contributing User

Join Date: Mar 2004

Location: Overland Park

Posts: 170

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C Oop?

Hello all. I am fairly new to C and am wanting to get my feet wet by recreating a popular game I used to play on my calculator. HickQuest.

I am coming to C from PHP and was just starting to get into OOP and using classes more and more often.

I am fearing that I may have to use C++ for this project of mine instead of C, which is what I want to use. Only C.

I am just learning to use structs (which seem much like classes to me) and am having a hard time figuring out how to link everything to gether much like you would a class.

Sadly, this is all I have come up with before having to post here.

Code:

#include <stdio.h>

#define deadLife 0

void Pause(void){
     char *c;
     printf("Press Enter to continue . . .\n");
     while((c = getchar()) != '\n'){ }
     free(c);
}

typedef struct {
        char *name;
        int minPower, maxPower;
        int maxLife, currentLife;
        char *currWeapon, *currShield;
} Enemies;

int main(void){
    printf("Hello.\n");
    Pause();
    return 0;
}

Should I be looking into ObjC?

TIA.

June 28th, 2006, 07:12 PM

para45

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Join Date: Mar 2006

Posts: 264

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A class (without all the bells and whistles of polymorphism and inheritance) is just a C-structure that has assoicated member functions. Then the class itself is merely just a collection of member data, same as a C-struct. In C++ the functions assoicated with a class are only accessable by calling them on a class instance, so if you were to make normal functions that operate on a structure you can get the same effect.

For example, in C++ a class may be defined as:

Code:

class square {
    public:
        square(int h, int w);
        int area();

    private:
        int height;
        int width;
}

square::square(int h, int w) {
    this->height = h;
    this->width = w;
}

int square::area() {
    return (this->height * this->width);
}

int main() {
    square s(10, 10);
    std::cout << "Area is " << s.area() << "\n";
    return 0;
}

In C this could be implemented as:

Code:

struct square {
        int height;
        int width;
}

void square_init(struct square* s, int h, int w) {
    s->height = h;
    s->width = w;
}

int square_area(struct square* s) {
    return (s->height * s->width);
}

int main() {
    struct square s;
    square_init(&s, 10, 10);
    printf("Area is %i\n", square_area(&s);
    return 0;
}

I would normally put all the square related functions in square.c and prefix them all with "square_", but that's just me.

In C++, class member functions are implemented in the same way as the above C code, where there is a hidden "this" parameter that is passed.

For example

Code:

square::square(int h, int w)

becomes

Code:

square::square(square* this, int h, int w)

The "this" pointer is a pointer to the object, in s.area() it's &s, or s->area() s.

Comments on this post

pumpkin head agrees: a very good explanation

Last edited by para45 : June 28th, 2006 at 07:15 PM.

June 28th, 2006, 07:47 PM

Spechal

Contributing User

Join Date: Mar 2004

Location: Overland Park

Posts: 170

Time spent in forums: 1 Day 12 h 42 m 8 sec
Reputation Power: 18

Quote:

Originally Posted by para45

In C++, class member functions are implemented in the same way as the above C code, where there is a hidden "this" parameter that is passed.

For example

Code:

square::square(int h, int w)

becomes

Code:

square::square(square* this, int h, int w)

The "this" pointer is a pointer to the object, in s.area() it's &s, or s->area() s.

All that bolded text made something click. I am a lot better off from where I was before, but still havent coded anything with this new information.

Thanks a lot. It really was a good explanation. The relations between C and C++ helped alot.

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