C 使用函数指针、结构、联合和枚举进行子类型化

前言：是的，这是家庭作业。上个星期左右，我一直在做这件事，谷歌搜索也帮不上忙。我不是在找人帮我完成作业，我更关心的是理解材料，我只是在寻找任何建设性的批评或朝着正确的方向推进

我有3个形状结构（圆形、三角形和矩形）、3个形状结构的并集、函数指针的结构、形状的枚举以及上述所有结构（并集、形状类型和函数指针）的结构

问题：我需要完成子类型/超级类型，以便驱动程序在不知道形状细节的情况下操作形状。我相信我已经完成了大部分框架，但是在函数指针和使用ShapeType enum和Shape struct实现它们方面有点迷失

原型.h

#include <my_struct.h>

void InitializeCircle(struct Shape *, double radius, double origin, double originY);
void InitializeRectangle(struct Shape *, double minX, double maxX, double minY, double maxY);
void InitializeTriangle(struct Shape *, Triangle *, double pt1X, double pt2X, double minY, double maxY);

double GetCircleArea(struct Shape *);
double GetCircleArea(struct Shape *);
double GetTriangleArea(struct Shape *);

void GetCircleBoundingBox(struct Shape *, double *);
void GetRectangleBoundingBox(struct Shape *, double *);
void GetTriangleBoundingBox(struct Shape *, double *);

// DEFINITIONS FOR THE THREE SHAPES:
typedef struct {
    double radius, origin, originY, area;
} Circle;

typedef struct {
    double pt1X, pt2X, minY, maxY, area;
} Triangle;

typedef struct {
    double minX, maxX, minY, maxY, area;
} Rectangle;


// SUBTYPING/SUPERTYPING:
struct Shape;   // Defined later

typedef struct {
    // Pointers to functions -> two data members: GetArea & GetBoundingBox
    double (*GetArea)(struct Shape *);
    GetArea = // NEED TO IMPLEMENT

    double (*GetBoundingBox)(struct Shape *, double *bbox);
    GetBoudingBox = // NEED TO IMPLEMENT

} FunctionTable;

typedef union {
    // Shape structs:
    Circle c;
    Triangle t;
    Rectangle r;
} ShapeUnion;

typedef enum {
    // Identifies the 3 types
    Circle,
    Rectangle,
    Triangle
} ShapeType;

typedef struct {
    ShapeUnion su;
    ShapeType st;
    FunctionTable ft;
} Shape;

我的结构c

/* This file should contain the 9 functions defined in prototypes.h */

#include <prototypes.h>

// Initialize Structs
void InitializeCircle(struct Shape *c, double r, double o, double oY) {
    c->radius = r;
    c->origin = o;
    c->originY = oY;
}
void InitializeRectangle(struct Shape *r, double miX, double maX, double miY, double maY) {
    r->minX = miX;
    r->maxX = maX;
    r->minY = miY;
    r->maxY = maY;
}
void InitializeTriangle(struct Shape *t, double p1X, double p2X, double miY, double maY) {
    t->pt1X = p1X;
    t->pt2X = p2X;
    t->minY = miY;
    t->maxY = maY;
}

// Get Area
double GetCircleArea(struct Shape *c) {
    c->area = 3.14159*c->radius*c->radius;
    return c->area;
}
double GetRectangleArea(struct Shape *r) {
    r->area = ((r->maxX-r->minX)*(r->maxY-r->minY));
    return r->area;
}
double GetTriangleArea(struct Shape *t) {
    t->area = (((t->pt2X-t->pt1X)*(t->maxY-t->minY))/2);
    return t->area;
}

// Get Bounding Box
void GetCircleBoundingBox(struct Shape *c, double *bbox) {
    bbox[0] = c->origin-c->radius;  // lower left corner
    bbox[1] = c->origin+c->radius;  // lower right corner
    bbox[2] = c->originY-c->radius; // upper left corner
    bbox[3] = c->originY+c->radius; // upper right corner
}
void GetRectangleBoundingBox(struct Shape *r, double *bbox) {
    bbox[0] = r->minX;
    bbox[1] = r->maxX;
    bbox[2] = r->minY;
    bbox[3] = r->maxY;
}
void GetTriangleBoundingBox(struct Shape *t, double *bbox) {
    bbox[0] = t->pt1X;  // minX
    bbox[1] = t->pt2X;  // maxX
    bbox[2] = 0;        // minY
    bbox[3] = t->maxY;  // maxY
}

#include <prototypes.h>
#include <stdio.h>

int main()
{
    struct Shape shapes[9];
    int i;

    InitializeCircle(shapes+0, 1, 0, 0);
    InitializeCircle(shapes+1, 1.5, 6, 8);
    InitializeCircle(shapes+2, 0.5, -3, 4);

    InitializeRectangle(shapes+3, 0, 1, 0, 1);
    InitializeRectangle(shapes+4, 1, 1.1, 10, 20);
    InitializeRectangle(shapes+5, 1.5, 3.5, 10, 12);

    InitializeTriangle(shapes+6, 0, 1, 0, 1);
    InitializeTriangle(shapes+7, 0, 1, 0, 0.1);
    InitializeTriangle(shapes+8, 0, 10, 0, 50);

    for (i = 0 ; i < 9 ; i++)
    {
        double bbox[4];
        printf("Shape %d\n", i);
        printf("\tArea: %f\n", shapes[i].ft.GetArea(shapes+i));
        shapes[i].ft.GetBoundingBox(shapes+i, bbox);
        printf("\tBbox: %f-%f, %f-%f\n", bbox[0], bbox[1], bbox[2], bbox[3]);
    }
}

/*此文件应包含prototype.h中定义的9个函数*/
#包括
//初始化结构
无效初始值圆形（结构形状*c，双r，双o，双oY）{
c->半径=r；
c->origin=o；
c->originY=oY；
}
void InitializeRectangle（结构形状*r，双重混合，双重最大值，双重最小值，双重可能）{
r->minX=miX；
r->maxX=maX；
r->minY=miY；
r->maxY=maY；
}
void InitializeTriangle（结构形状*t，双p1X，双p2X，双miY，双maY）{
t->pt1X=p1X；
t->pt2X=p2X；
t->minY=miY；
t->maxY=maY；
}
//获取区域
双GetCircleArea（结构形状*c）{
c->面积=3.14159*c->半径*c->半径；
返回c->区域；
}
双GetRectangleArea（结构形状*r）{
r->area=（（r->maxX-r->minX）*（r->maxY-r->minY））；
返回r->区域；
}
双GetTriangelArea（结构形状*t）{
t->area=（（t->pt2X-t->pt1X）*（t->maxY-t->minY））/2）；
返回t->区域；
}
//获取边界框
void GetCircleBoundingBox（结构形状*c，双*bbox）{
bbox[0]=c->原点-c->半径；//左下角
bbox[1]=c->原点+c->半径；//右下角
bbox[2]=c->originY-c->radius；//左上角
bbox[3]=c->originY+c->radius；//右上角
}
void GetRectangleBoundingBox（结构形状*r，双*bbox）{
bbox[0]=r->minX；
bbox[1]=r->maxX；
bbox[2]=r->minY；
bbox[3]=r->maxY；
}
void gettriangelboundingbox（结构形状*t，双*bbox）{
bbox[0]=t->pt1X；//minX
bbox[1]=t->pt2X；//maxX
bbox[2]=0；//minY
bbox[3]=t->maxY；//maxY
}

驱动程序.c

/* This file should contain the 9 functions defined in prototypes.h */

#include <prototypes.h>

// Initialize Structs
void InitializeCircle(struct Shape *c, double r, double o, double oY) {
    c->radius = r;
    c->origin = o;
    c->originY = oY;
}
void InitializeRectangle(struct Shape *r, double miX, double maX, double miY, double maY) {
    r->minX = miX;
    r->maxX = maX;
    r->minY = miY;
    r->maxY = maY;
}
void InitializeTriangle(struct Shape *t, double p1X, double p2X, double miY, double maY) {
    t->pt1X = p1X;
    t->pt2X = p2X;
    t->minY = miY;
    t->maxY = maY;
}

// Get Area
double GetCircleArea(struct Shape *c) {
    c->area = 3.14159*c->radius*c->radius;
    return c->area;
}
double GetRectangleArea(struct Shape *r) {
    r->area = ((r->maxX-r->minX)*(r->maxY-r->minY));
    return r->area;
}
double GetTriangleArea(struct Shape *t) {
    t->area = (((t->pt2X-t->pt1X)*(t->maxY-t->minY))/2);
    return t->area;
}

// Get Bounding Box
void GetCircleBoundingBox(struct Shape *c, double *bbox) {
    bbox[0] = c->origin-c->radius;  // lower left corner
    bbox[1] = c->origin+c->radius;  // lower right corner
    bbox[2] = c->originY-c->radius; // upper left corner
    bbox[3] = c->originY+c->radius; // upper right corner
}
void GetRectangleBoundingBox(struct Shape *r, double *bbox) {
    bbox[0] = r->minX;
    bbox[1] = r->maxX;
    bbox[2] = r->minY;
    bbox[3] = r->maxY;
}
void GetTriangleBoundingBox(struct Shape *t, double *bbox) {
    bbox[0] = t->pt1X;  // minX
    bbox[1] = t->pt2X;  // maxX
    bbox[2] = 0;        // minY
    bbox[3] = t->maxY;  // maxY
}

#include <prototypes.h>
#include <stdio.h>

int main()
{
    struct Shape shapes[9];
    int i;

    InitializeCircle(shapes+0, 1, 0, 0);
    InitializeCircle(shapes+1, 1.5, 6, 8);
    InitializeCircle(shapes+2, 0.5, -3, 4);

    InitializeRectangle(shapes+3, 0, 1, 0, 1);
    InitializeRectangle(shapes+4, 1, 1.1, 10, 20);
    InitializeRectangle(shapes+5, 1.5, 3.5, 10, 12);

    InitializeTriangle(shapes+6, 0, 1, 0, 1);
    InitializeTriangle(shapes+7, 0, 1, 0, 0.1);
    InitializeTriangle(shapes+8, 0, 10, 0, 50);

    for (i = 0 ; i < 9 ; i++)
    {
        double bbox[4];
        printf("Shape %d\n", i);
        printf("\tArea: %f\n", shapes[i].ft.GetArea(shapes+i));
        shapes[i].ft.GetBoundingBox(shapes+i, bbox);
        printf("\tBbox: %f-%f, %f-%f\n", bbox[0], bbox[1], bbox[2], bbox[3]);
    }
}

#包括
#包括
int main（）
{
结构形状[9]；
int i；
初始化圆形（形状+0,1,0,0）；
初始化圆形（形状+1,1.5,6,8）；
初始化圆形（形状+2,0.5，-3,4）；
初始化矩形（形状+3,0,1,0,1）；
初始化矩形（形状+4,1,1.1,10,20）；
初始化矩形（形状+5,1.5,3.5,10,12）；
初始化角度（形状+6,0,1,0,1）；
初始化角度（形状+7,0,1,0,0.1）；
初始化角度（形状+8,0,10,0,50）；
对于（i=0；i<9；i++）
{
双bbox[4]；
printf（“形状%d\n”，i）；
printf（“\tArea:%f\n”，shapes[i].ft.GetArea（shapes+i））；
shapes[i].ft.GetBoundingBox（shapes+i，bbox）；
printf（“\tbox:%f-%f，%f-%f\n”，bbox[0]，bbox[1]，bbox[2]，bbox[3]）；
}
}

---

如有任何见解，将不胜感激。再说一次，我不是在找人帮我做作业，我只是希望能克服这个障碍。

您需要为每种类型定义函数表：

// This is global, and used for all circle types. 
// Could be declared 'static' if table and init functions are in the same file.
FunctionTable const CircleFuncs = {
    GetCircleArea,
    GetCircleBoundingBox
};

由于表可以为同一类型的所有形状共享，因此我们只需要指针：

typedef struct Shape { // <- note the fixed type name also
    ShapeUnion su;
    ShapeType st;
    FunctionTable const * ft;
} Shape;

---

您不能用InitializeXYZ中的相关函数指针设置函数表吗？@AlanAu谢谢您的输入！我相信我可以，但是如果这个任务的重点是在我的FunctionTable结构中实现函数指针“GetArea”和“GetBoundingBox”。不幸的是，没有办法解决这个问题。但您不能将代码体直接放入结构定义中。因此，您必须在其他地方实现这些功能。然后在初始化函数中，用指向实际实现的函数的指针填充FunctionTable结构成员。除非我完全误解了你的要求和

typedef结构{…}形状不是相同的类型。后者需要是
typedef结构形状{…}形状