C/C++用状态转移表联合函数指针数组实现状态机FSM

状态机在工程中使用非常的频繁，有如下常见的三种实现方法：

1.

switch-case

实现，适合简单的状态机；

2. 二维状态表

state-event

实现，逻辑清晰，但是矩阵通常比较稀疏，而且维护麻烦；

3. 用状态转移表

stateTransfer Table

实现，数组大小等于状体转移边个数，易扩展；

下面用一个例子来进行详细说明，描述的如下场景：

描述对象：门

状态：开着、关着、锁着 (这里的关着指关了但未锁的状态)

事件：开门、关门、上锁、解锁

代码实现用枚举来定义状态和事件，操作数据节点转移到目的状态用函数实现。枚举本身默认是从0开始的

int

类型，利用这个特点将状态转移函数放到函数指针数组中与状态对应起来，方便操作。

核心数据结构如下：

状态：枚举类型

事件：枚举类型

状态转移结构体：{当前状态、事件、下个状态}，定义一个全局数组来使用

状态变更函数：到下个状态(放到数组中与状态枚举对应起来)

此种实现方法容易扩展，增加状态和事件都比较容易。如果存在一个状态通过对应事件可以转移到多个状态的情形，则可以扩展状态转移函数，或者在状态转移结构中增加一个判断函数字段。

代码实现如下：

#include <iostream>
using namespace std;

typedef enum{
OPENED,
CLOSED,
LOCKED,
}  State;

typedef enum{
OPEN,
CLOSE,
LOCK,
UNLOCK
} Event;

typedef struct{
State currentState;
Event event;
State NextState;
} StateTransfer;

typedef struct{
State state;
int transferTimes;
}Door;

StateTransfer g_stateTransferTable[]{
{OPENED, CLOSE,  CLOSED},
{CLOSED, OPEN,   OPENED},
{CLOSED, LOCK,   LOCKED},
{LOCKED, UNLOCK, CLOSED},
};

void toOpen(Door& door);
void toClose(Door& door);
void toLock(Door& door);
typedef void (*pfToState)(Door& door);
pfToState g_pFun[] = {toOpen, toClose, toLock}; //状态枚举值对应下标

void toOpen(Door& door){
door.state = OPENED;
cout << "open the door!\n";
}

void toClose(Door& door){
door.state = CLOSED;
cout << "close the door!\n";
}

void toLock(Door& door){
door.state = LOCKED;
cout << "lock the door!\n";
}

void transfer(Door& door,const Event event){
for (int i = 0; i < sizeof(g_stateTransferTable)/sizeof(StateTransfer); ++i) {
if(door.state == g_stateTransferTable[i].currentState &&
event == g_stateTransferTable[i].event){
g_pFun[g_stateTransferTable[i].NextState](door);
door.transferTimes++;
cout << "transfer ok!\n";
return;
}
}
cout << "This event cannot transfer current state!!\n";
return;
}

void printDoor(const Door& door){
string stateNote[] = {"opened","closed","locked"}; // 下标正好对应状态枚举值
cout << "the door's state is: " << stateNote[door.state] << endl;
cout << "the door transfer times is: " << door.transferTimes << endl;
}

int main(){
Door door = {CLOSED, 0};
printDoor(door);
transfer(door, OPEN);
printDoor(door);
transfer(door, LOCK);
printDoor(door);
transfer(door, CLOSE);
printDoor(door);
return 0;
}

运行结果如下：

the door’s state is: closed

the door transfer times is: 0

open the door!

transfer ok!

the door’s state is: opened

the door transfer times is: 1

This event cannot transfer current state!!

the door’s state is: opened

the door transfer times is: 1

close the door!

transfer ok!

the door’s state is: closed

the door transfer times is: 2