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_Htypedef struct shape_t {    void *shapeData;    void (*area)(void *);    void (*release)(void *);}Shape;#endif

circle.h 圆形接口

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

circle.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_Htypedef 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 
     
      #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
      
       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