C++ 将类插入到地图容器中
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C++ Inserting a class into a map container
提问by Fouf
I have a map in C++ and I wish to input my class as the value, and a string as the key.
When I try to, I get an error 'Scene_Branding' : illegal use of this type as an expressionI get an illegal use of this type as an expression, and I can't seem to find out why. Here is some code.
我有一个 C++ 映射，我希望输入我的类作为值，并输入一个字符串作为键。当我尝试时，我收到一个错误，'Scene_Branding' : illegal use of this type as an expression我将这种类型作为表达式非法使用，但我似乎无法找出原因。这是一些代码。
string CurrentScene = "Scene_Branding";
map<string, Scene> Scenes;
Scenes.insert(std::make_pair("Scene_Branding", Scene_Branding)); //<-- Illegal Error parameter 2
and here is Scene Branding header..
这是场景品牌标题..
#ifndef Scene_Branding_H
#define Scene_Branding_H
#include "Scene.h"
#include <iostream>
#include <string>
class Scene_Branding : Scene
{
public:
Scene_Branding();
~Scene_Branding();
void Draw();
};
#endif
and here is Scene header..
这是场景标题..
#ifndef Scene_H
#define Scene_H
#include <iostream>
#include <string>
class Scene
{
public:
Scene();
~Scene();
virtual void Draw();
};
#endif
and here is there cpp files.
这里有 cpp 文件。
Scene cpp.
场景 cpp。
#include "Scene.h"
Scene::Scene()
{
}
Scene::~Scene()
{
}
void Scene::Draw(){
std::cout << "Hey";
}
Scene_Branding cpp
Scene_Branding cpp
#include "Scene_Branding.h"
Scene_Branding::Scene_Branding()
{
}
Scene_Branding::~Scene_Branding()
{
}
void Scene_Branding::Draw()
{
std::cout << "Drawing from Scene_branding";
}
回答by erelender
First, don't store objects themselves in the map, store pointers to your objects.
首先，不要将对象本身存储在地图中，而是存储指向对象的指针。
Second, you need to give an instance of Scene_Branding to std::make_pair, not the class itself.
其次，您需要将 Scene_Branding 的实例提供给 std::make_pair，而不是类本身。
EDIT: Here's how you go about storing pointers:
编辑：这是您如何存储指针：
string CurrentScene = "Scene_Branding";
map<string, Scene*> Scenes;
Scenes.insert(std::make_pair("Scene_Branding", new Scene_Branding()));
But, since you asked this type of question, i recommend you read a good c++ book for further grasping of concepts like pointers.
但是，既然你问了这类问题，我建议你阅读一本好的 C++ 书，以进一步掌握指针等概念。
回答by Alexander Gessler
Try:
尝试：
Scenes.insert(std::make_pair("Scene_Branding", Scene_Branding()));
回答by Matthieu M.
I think you don't want to do that.
我想你不想那样做。
- there is no runtime type-mapping in C++, you store objects, not types.
- you cannot store polymorphic types in STL containers, use
boost::ptr_mapinstead if it is your wish
- C++ 中没有运行时类型映射，你存储的是对象，而不是类型。
- 你不能在 STL 容器中存储多态类型，
boost::ptr_map如果你愿意，可以改用
So, the "new" code:
所以，“新”代码：
class Scene
{
public:
virtual ~Scene(); // Virtual Destructor, it's a base class
virtual Scene* clone() const = 0; // Polymorphic construction
private:
// whatever you wish
};
class Scene_Branding: public Scene
{
public:
virtual Scene_Branding* clone() const { return new Scene_Branding(); }
};
And the new way to store those:
以及存储这些的新方法：
const std::string SceneBrandingKey = "Scene_Branding";
typedef boost::ptr_map<std::string, Scene> scenes_type;
scenes_type Scenes;
Scenes.insert(SceneBrandingKey, new Scene_Branding());
And you can use it thusly:
你可以这样使用它：
Scenes["Scene_Branding"].process(); // Note: use '.' not '->'
The nice thing about Boost Pointer Containeris that it's been meant for polymorphic types, with exception safety and all, and yet mimics the behavior / interface of the STL so that you are not lost :)
约的好处升压指针集装箱是，它已经意味着多态类型，具有异常安全和所有，然而模仿STL的行为/接口，因此你不会丢失:)
回答by Javier Gutiérrez-Maturana Sánc
You need pointers in class when use generic map containers else, the result is possible a new object empty of your class... with pointers works!
当使用其他通用映射容器时，您需要类中的指针，结果可能是您的类中空的新对象......使用指针可以工作！
std::map<std::string, Type*> map_;
Insert
插入
map_["key"] = *Type;
NOTE: if -fpermisive flag to compiler is not set you need pass *Type not const when insert in the map_ container.
注意：如果未设置编译器的 -fpermisive 标志，则在插入 map_ 容器时需要传递 *Type not const。
Best Regards,
此致，
Javier,
哈维尔，
