从静态函数调用非静态变量 [英] Calling a non-static variable from a static function

问题描述

我在学习C ++的过程中遇到了一个问题，我不知道如何处理这种情况：

I encountered an issue while trying to do something in the process of learning C++ and I am not sure how to handle the situation:

class Command
{
  public:
    const char *       Name;
    uint32             Permission;
    bool (*Handler)(EmpH*, const char* args); // I do not want to change this by adding more arguments
};
class MyClass : public CommandScript
{
 public:
  MyClass() : CommandScript("listscript") { }
  bool isActive = false;
  Command* GetCommands() const
  {
      static Command commandtable[] =
      {
          { "showlist", 3, &DoShowlistCommand } // Maybe handle that differently to fix the problem I've mentioned below?
      };
      return commandtable;
  }
  static bool DoShowlistCommand(EmpH * handler, const char * args)
  {
     // I need to use isActive here for IF statements but I cannot because
     // DoShowlistCommand is static and isActive is not static. 
     // I cannot pass it as a parameter either because I do not want to
     // change the structure of class Command at all

     // Is there a way to do it?
  }
};

任何帮助将非常感谢！ ：）

Any help would be greatly appreciated! :)

推荐答案

这里有两个潜在的答案：

There are two potential answers here:

如我们以前的问题/答案，这是不可能的，除非你在静态函数中有一个特定的 MyClass object（并使用 object.isActive ）。很遗憾，您无法在此处执行此操作：

As said in our previous question/answer, this is not possible, unless you'd have in the static function a specific MyClass object (and use object.isActive). Unfortunately, you can't do this here :

• 您的代码注释清楚地表明您不能添加 MyClass 参数到函数调用;


• 现有的参数并不表示您已经有一个指向父类对象的指针;


• 它不适合使用全局对象这样的上下文。

• your code comments clearly show that you can't add a MyClass parameter to the function call;
• the existing parameters don't suggest that you have already a pointer to parent class object;
• it would not be adivsable to use global objects in such a context.

似乎您希望有静态函数，因为你想在一个表中提供它，脚本命令函数指针。

It seems that you want to have the function static, because you want to provide it in a table that maps script-commands to function pointers.

替代A

如果<$ c $中使用所有函数指针c> commandtable 是 MyClass 的成员，你可以想到使用指向成员函数的指针，而不是指向函数的指针。在对象上设置isActive的外部对象/函数可以将指针引用到它所知道的MyClass对象上的成员函数。

If all the function pointers used in commandtable are members of MyClass, you could think of using a pointer to a member function instead of a pointer to a function. The outside object/function that sets isActive on an object, could then refer the pointer to the member function, on the MyClass object it knows.

替代B

修改代码的设计以实现脚本引擎通过使用命令设计模式：它非常适合此类问题。这将需要一些重构你的代码，但它将是如此更加可维护和可扩展性后！

Revise the design of your code to implement your script engine by using the command design pattern: it's ideally suited for this kind of problems. It will require some refactoring of your code, but it will be so much more maintenable and extensible afterwards !

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