我倒不是为了OOP而OOP，实在是OOP的一些特征，例如封装，多态其实是软件工程思想，这些思想不分语言，遵循了这些思想可以使得程序更有弹性，更易修改和维护，避免僵化，脆弱

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shape.h 该文件定义的是图形接口，所有具体图形都必须实现自己计算面积，周长等API

#ifndef SHAPE_H
#define SHAPE_H

typedef struct shape_t
{
void *shapeData;
void (*area)(void *);
void (*release)(void *);
}Shape;

#endifcircle.h 圆形接口

#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);

#endifcircle.c 圆形的实现代码，static修饰的函数其实相当于private函数

#include
#include
#include
#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);

#endifsquare.c

#include
#include
#include
#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 所有的工作，都为了它，是为了让它的代码稳定

#include
#include "shape.h"
#include "circle.h"
#include "square.h"

void printShapeArea(Shape **shape,int length)
{
int i=0;
for(i=0;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;
}

总结：

printShapeArea 函数并不知道传入的图形列表分别都是哪些图形，这些图形又都怎么计算面积和周长，它唯一知道的是，这些图形计算面积和周长的接口是什么，通过这个接口计算就好了