我在这里使用指针吗？ [英] Do I _have to_ use a pointer here?

问题描述

我遇到这个问题的时间&再次，我一直使用一个向前的声明和指针来解决它。

I've run into this problem time & again, and I've always had to resolve it using a forward declaration and a pointer.

这似乎是错误的C ++ 需要一个工作以获得合作的对象。有没有办法让这个编译，而不使Mesh *类中的一个指针（或向量< Tri> into vector< Tri * > ？

It seems wrong that C++ requires a work around to get objects to co-operate. Is there any way to get this to compile WITHOUT making Mesh* a pointer in class Shape (or, the vector<Tri> into vector<Tri*>?

#ifndef S
#define S

#include "Mesh.h"
//class Mesh ; //delete line above, uncomment this to make it work
class Shape // a mathematical shape
{
    Mesh mesh ; // the poly mesh repr' this math shape
    //Mesh *mesh ; // make it work

    // a shape must be intersectable by a ray
    //virtual Intersection intersects( const Ray& ray )=0 ;
} ;

#endif

Mesh.h

Mesh.h

#ifndef M
#define M

#include <vector>
using namespace std;
#include "Triangle.h"

struct Mesh
{
    vector<Triangle> tris ; // a mesh is a collection of triangles
} ;

#endif

Triangle.h

Triangle.h

#ifndef T
#define T
#include "Shape.h"
class Triangle : public Shape
{
    // a triangle must be intersectable by a ray
    // a triangle's mesh is simple but it is still a mesh (1 poly)
} ;
#endif

推荐答案

一个指针（当然，在 std :: vector 中使用指针）。你只需要仔细分析你的依赖。 Triangle 继承 Shape ，因此 Shape 的定义在上 Triangle 的。 形状包含网格，因此 Mesh 的定义先于形状的。这会给出顺序：网格，形状，三角形，它们可以毫无问题地编译。

It works for me without a pointer (there are, naturally, pointers used inside std::vector). You just have to analyze your dependencies carefully. Triangle inherits Shape, therefore Shape's definition is above Triangle's. Shape contains a Mesh, therefore Mesh's definition precedes Shape's. This gives the order: Mesh, Shape, Triangle, which compiles without errors.

当然，一些网格物体必须有空矢量，因为矢量内部的每个三角形都需要一个网格物体。

Naturally, some meshes will have to have empty vectors, since every triangle inside the vector itself requires a mesh.

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