用于状态机

若水般的淡然安静女子 2024-07-15 10:03:25

我会在哪些编程领域使用状态机？

使用状态机来表示一个（真实的或逻辑的）对象，该对象可以存在于有限数量的条件（“状态”）中，并根据一组固定的规则从一个状态进展到下一个状态。

为什么要使用状态机？

状态机通常是一种非常紧凑的方式来表示一组复杂的规则和条件，并处理各种输入。您将在内存有限的嵌入式设备中看到状态机。如果实施得当，状态机是自记录的，因为每个逻辑状态都代表一种物理条件。与程序等价物相比，状态机可以用极少的代码来实现，并且运行效率极高。此外，管理状态变化的规则通常可以作为数据存储在表中，提供易于维护的紧凑表示。

我该如何实施？

简单的例子：

enum states {      // Define the states in the state machine.
  NO_PIZZA,        // Exit state machine.
  COUNT_PEOPLE,    // Ask user for # of people.
  COUNT_SLICES,    // Ask user for # slices.
  SERVE_PIZZA,     // Validate and serve.
  EAT_PIZZA        // Task is complete.
} STATE;

STATE state = COUNT_PEOPLE;
int nPeople, nSlices, nSlicesPerPerson;

// Serve slices of pizza to people, so that each person gets
/// the same number of slices.   
while (state != NO_PIZZA)  {
   switch (state)  {
   case COUNT_PEOPLE:  
       if (promptForPeople(&nPeople))  // If input is valid..
           state = COUNT_SLICES;       // .. go to next state..
       break;                          // .. else remain in this state.
   case COUNT_SLICES:  
       if (promptForSlices(&nSlices))
          state = SERVE_PIZZA;
        break;
   case SERVE_PIZZA:
       if (nSlices % nPeople != 0)    // Can't divide the pizza evenly.
       {                             
           getMorePizzaOrFriends();   // Do something about it.
           state = COUNT_PEOPLE;      // Start over.
       }
       else
       {
           nSlicesPerPerson = nSlices/nPeople;
           state = EAT_PIZZA;
       }
       break;
   case EAT_PIZZA:
       // etc...
       state = NO_PIZZA;  // Exit the state machine.
       break;
   } // switch
} // while

注释：

为简单起见，该示例使用具有显式 case/break 状态的 switch()。实际上，case 通常会“失败”到下一个状态。
为了便于维护大型状态机，每个case中完成的工作可以封装在“worker”函数中。 while()顶部的任何输入，将其传递给辅助函数，并检查辅助函数的返回值以计算下一个状态。
为了紧凑，整个 switch() 可以用函数指针数组替换。每个状态都由一个函数体现，该函数的返回值是指向下一个状态的指针。 警告：这会简化状态机或使其完全不可维护，因此请仔细考虑实现！
嵌入式设备可以实现为仅在发生灾难性错误时退出的状态机，之后执行硬重置并重新进入状态机。

In what areas of programming would I use a state machine?

Use a state machine to represent a (real or logical) object that can exist in a limited number of conditions ("states") and progresses from one state to the next according to a fixed set of rules.

Why would I use a state machine?

A state machine is often a very compact way to represent a set of complex rules and conditions, and to process various inputs. You'll see state machines in embedded devices that have limited memory. Implemented well, a state machine is self-documenting because each logical state represents a physical condition. A state machine can be embodied in a tiny amount of code in comparison to its procedural equivalent and runs extremely efficiently. Moreover, the rules that govern state changes can often be stored as data in a table, providing a compact representation that can be easily maintained.

How can I implement one?

Trivial example:

enum states {      // Define the states in the state machine.
  NO_PIZZA,        // Exit state machine.
  COUNT_PEOPLE,    // Ask user for # of people.
  COUNT_SLICES,    // Ask user for # slices.
  SERVE_PIZZA,     // Validate and serve.
  EAT_PIZZA        // Task is complete.
} STATE;

STATE state = COUNT_PEOPLE;
int nPeople, nSlices, nSlicesPerPerson;

// Serve slices of pizza to people, so that each person gets
/// the same number of slices.   
while (state != NO_PIZZA)  {
   switch (state)  {
   case COUNT_PEOPLE:  
       if (promptForPeople(&nPeople))  // If input is valid..
           state = COUNT_SLICES;       // .. go to next state..
       break;                          // .. else remain in this state.
   case COUNT_SLICES:  
       if (promptForSlices(&nSlices))
          state = SERVE_PIZZA;
        break;
   case SERVE_PIZZA:
       if (nSlices % nPeople != 0)    // Can't divide the pizza evenly.
       {                             
           getMorePizzaOrFriends();   // Do something about it.
           state = COUNT_PEOPLE;      // Start over.
       }
       else
       {
           nSlicesPerPerson = nSlices/nPeople;
           state = EAT_PIZZA;
       }
       break;
   case EAT_PIZZA:
       // etc...
       state = NO_PIZZA;  // Exit the state machine.
       break;
   } // switch
} // while

Notes:

The example uses a switch() with explicit case/break states for simplicity. In practice, a case will often "fall through" to the next state.
For ease of maintaining a large state machine, the work done in each case can be encapsulated in a "worker" function. Get any input at the top of the while(), pass it to the worker function, and check the return value of the worker to compute the next state.
For compactness, the entire switch() can be replaced with an array of function pointers. Each state is embodied by a function whose return value is a pointer to the next state. Warning: This can either simplify the state machine or render it totally unmaintainable, so consider the implementation carefully!
An embedded device may be implemented as a state machine that exits only on a catastrophic error, after which it performs a hard reset and re-enters the state machine.

用于状态机

如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

评论（18）

我会在哪些编程领域使用状态机？

为什么要使用状态机？

我该如何实施？

In what areas of programming would I use a state machine?

Why would I use a state machine?

How can I implement one?

关于作者

相关话题

热门标签

推荐作者

qq_FjTq5B

18273202778

WordPress小学生

〃温暖了心ぐ

迷乱花海

niuniu

友情链接

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。