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};
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"};
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
