C language implementation of OOP

I would not for OOP and OOP, it is some of the characteristics of OOP , such as encapsulation , polymorphism is actually software engineering ideas , these ideas , regardless of language , follow these ideas can make the program more flexible and easier to modify and maintain avoid rigid, fragile

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shape.h This file defines the graphical interface must implement all the specific graphics themselves calculate the area , perimeter and other API

#ifndef SHAPE_H 
#define SHAPE_H 
 
typedef struct shape_t  
{ 
    void *shapeData; 
    void (*area)(void *); 
    void (*release)(void *); 
}Shape; 
 
#_endif

circle.h Round Interface

#ifndef CIRCLE_H 
#define CIRCLE_H 
 
typedef struct 
{ 
    double r; 
}CircleData; 
 
typedef struct  
{ 
    void *shapeData; 
    void (*area)(void *); 
    void (*release)(void *); 
}Circle; 
 
Circle *makeCircle(double r); 
 
#_endif

circle.c Round implementation code , static decorated function is the equivalent private function

#include <assert.h> 
#include <stdlib.h> 
#include <stdio.h> 
#include "circle.h" 
 
const double PI = 3.14159; 
 
static void area(void *shape) 
{ 
    Circle *_circle = (Circle *)shape; 
    CircleData* data = (CircleData*)_circle->shapeData; 
    printf("the circle area is %f \n", data->r * data->r * PI); 
} 
 
static void release(void *shape) 
{ 
    Circle *_circle = (Circle *)shape; 
    CircleData* data = (CircleData*)_circle->shapeData; 
    free(data); 
    free(_circle); 
} 
 
Circle *makeCircle(double r) 
{ 
    CircleData* circleData = (CircleData*)malloc(sizeof(CircleData)); 
    Circle* circle = (Circle*)malloc(sizeof(Circle)); 
    assert(circleData != NULL); 
    assert(circle != NULL); 
    assert(r > 0); 
 
     
    circleData->r = r; 
    circle->shapeData = circleData; 
    circle->area = &area; 
    circle->release = &release; 
 
    return circle; 
}

square.h

#ifndef SQUARE_H 
#define SQUARE_H 
 
typedef struct 
{ 
    double x; 
    double y; 
}SquareData; 
 
typedef struct  
{ 
    void *shapeData; 
    void (*area)(void *); 
    void (*release)(void *); 
}Square; 
 
Square *makeSquare(double x, double y); 
 
#_endif

square.c

#include <assert.h> 
#include <stdlib.h> 
#include <stdio.h> 
#include "square.h" 
 
static void area(void *shape) 
{ 
    Square *square = (Square *)shape; 
    SquareData* data = (SquareData*)square->shapeData; 
    printf("the square area is %f \n", data->x * data->y); 
} 
 
static void release(void *shape) 
{ 
    Square *square = (Square *)shape; 
    SquareData* data = (SquareData*)square->shapeData; 
    free(data); 
    free(square); 
} 
 
Square *makeSquare(double x, double y) 
{ 
    SquareData* squareData = (SquareData*)malloc(sizeof(SquareData)); 
    Square* square = (Square*)malloc(sizeof(Square)); 
    assert(squareData != NULL); 
    assert(square != NULL); 
    assert(x > 0 && y > 0); 
 
    squareData->x = x; 
    squareData->y = y; 
    square->shapeData = squareData; 
    square->area = &area; 
    square->release = &release; 
 
    return square; 
}

main.c all the work , all for it , is the code to make it stable

#include <stdio.h> 
#include "shape.h" 
#include "circle.h" 
#include "square.h" 
 
void printShapeArea(Shape **shape,int length) 
{ 
    int i=0; 
    for(i=0;i<length;i++) 
    { 
        shape[i]->area(shape[i]); 
        shape[i]->release(shape[i]); 
    } 
} 
 
int main() 
{ 
    Shape *p[3] = {(Shape*)makeCircle(3.2),(Shape*)makeCircle(3.2),(Shape*)makeSquare(3.1,4)}; 
    printShapeArea(p,3); 
    return 0; 
}

Summary :

printShapeArea function does not know the incoming graphic list , respectively, which are the graphics, which are how they calculate the area and perimeter, it is only known that these graphical interface to calculate the area and perimeter of what is , through this interface is calculated like