C++：如何使在同一个 .cpp 上声明的两个类“看到”编译时彼此？

发布于 2024-12-15 11:07:39 字数 639 浏览 3 评论 0原文

在 VS2008 上编译此代码时：

  #include <vector>

using namespace std;

class Vertex {

public: double X; 
        double Y;
        double Z;

        int id; // place of vertex in original mesh vertex list

        vector<Vertex*> neighbor; //adjacent vertices

        vector<Triangle*> face; // adjacent triangles

        float cost; // saved cost of collapsing edge

        Vertex *collapse; // 
};



 class Triangle {

public:
    Vertex * vertex[3]; 


};

出现以下错误：

1>.\Triangle.cpp(15) : error C2065: 'Triangle' : undeclared identifier

如何解决此问题？

原文

When compiling this code on VS2008:

  #include <vector>

using namespace std;

class Vertex {

public: double X; 
        double Y;
        double Z;

        int id; // place of vertex in original mesh vertex list

        vector<Vertex*> neighbor; //adjacent vertices

        vector<Triangle*> face; // adjacent triangles

        float cost; // saved cost of collapsing edge

        Vertex *collapse; // 
};



 class Triangle {

public:
    Vertex * vertex[3]; 


};

I get the following error:

1>.\Triangle.cpp(15) : error C2065: 'Triangle' : undeclared identifier

How can I fix this?

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清风疏影 2024-12-22 11:07:39

您可以使用前向声明：

class Traingle;

class Vertex
{
    ...
};

class Triangle
{
    ...
};

类型的前向声明（例如class Triangle）允许您声明该类型的指针或引用，但不能声明该类型的对象。换句话说，

class Triangle;
class Vertex
{
  vector<Triangle*> face;
};

会编译，但

class Triangle;
class Vertex
{
  vector<Triangle> face;
};

不会编译。

此外，类型的前向声明不允许您访问其成员，因为编译器还不知道它们。因此，使用前向声明类型的对象的成员函数必须在类型完全定义之后定义。在您的情况下，在 class Triangle 的定义之后。

哦，这根本不是 Visual Studio 特有的。这只是标准的 C++。

You use a forward declaration:

class Traingle;

class Vertex
{
    ...
};

class Triangle
{
    ...
};

A forward declaration of a type (e. g. class Triangle) allows you to declare pointers or references to that type, but not objects of the type. In other words

class Triangle;
class Vertex
{
  vector<Triangle*> face;
};

will compile, but

class Triangle;
class Vertex
{
  vector<Triangle> face;
};

will not compile.

Also, a forward declaration of a type does not let you access its members, because the compiler does not know about them yet. So the member functions that use objects of the forward declared type must be defined after the type is fully defined. In your case, after the definition of class Triangle.

Oh, and this is not at all specific to Visual Studio. This is just standard C++.

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路还长，别太狂 2024-12-22 11:07:39

您需要在 Vertex 类之前转发声明 Triangle 类。在这种情况下，看起来像这样：

#include <vector>

using namespace std;

class Triangle;

class Vertex {
public:
        double X; 
        double Y;
        double Z;

        int id; // place of vertex in original mesh vertex list

        vector<Vertex*> neighbor; //adjacent vertices
        vector<Triangle*> face; // adjacent triangles
        float cost; // saved cost of collapsing edge

        Vertex *collapse; // 
};

class Triangle {
public:
    Vertex * vertex[3]; 
};

这个上一个问题似乎包含很好的细节关于前向声明。

You need to forward declare the Triangle class before the Vertex class. In this case that would look something like this:

#include <vector>

using namespace std;

class Triangle;

class Vertex {
public:
        double X; 
        double Y;
        double Z;

        int id; // place of vertex in original mesh vertex list

        vector<Vertex*> neighbor; //adjacent vertices
        vector<Triangle*> face; // adjacent triangles
        float cost; // saved cost of collapsing edge

        Vertex *collapse; // 
};

class Triangle {
public:
    Vertex * vertex[3]; 
};

This previous question seems to contain good details about forward declaration.

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