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状态机的实现无非就是3个要素：状态，事件，响应。转换成具体的行为就3句话

发生了什么事？

现在系统处在什么状态？

在这样的状态下发生了这样的事，系统要干什么？

举例--工作管理系统

#include <stdio.h>  
#include <stdlib.h>  
#include <string.h>  
  
// 定义状态枚举  
typedef enum {  
    STATE_IDLE,  
    STATE_WORKING,  
    STATE_DONE,  
    STATE_ERROR  
} ToolState;  
  
// 定义状态机结构体  
typedef struct {  
    ToolState currentState;  
} ToolStateMachine;  
  
// 状态转换函数  
void transitionToIdle(ToolStateMachine *sm)
{
    sm->currentState = STATE_IDLE;  
    printf("Tool is idle.\n");  
}
  
void transitionToWorking(ToolStateMachine *sm) {  
    sm->currentState = STATE_WORKING;  
    printf("Tool is working.\n");  
    // 在这里执行实际的工作  
}  
  
void transitionToDone(ToolStateMachine *sm) {  
    sm->currentState = STATE_DONE;  
    printf("Tool is done.\n");  
}  
  
void transitionToError(ToolStateMachine *sm) {  
    sm->currentState = STATE_ERROR;  
    printf("Tool encountered an error.\n");  
}  

// 处理用户输入的函数  
void processInput(ToolStateMachine *sm, const char *input) 
{
   if(strcmp(input, "start")==0)
   {
        if(sm->currentState == STATE_IDLE)
        {
            transitionToWorking(sm);
        }
        else
        {
            printf("Cannot start while not in idle state.\n");
        }
   }
   else if(strcmp(input,"stop")==0)
   {
        if(sm->currentState == STATE_WORKING)
        {
            transitionToDone(sm);
        }
        else
        {
            printf("Cannot stop while not working.\n");
        }
   }
   else if(strcmp(input,"invalid")==0)
   {
        transitionToError(sm);
   }
   else
   {
     printf("Unknown command.\n"); 
   }
}


int main(void)
{
    ToolStateMachine sm = {STATE_IDLE};

    //模拟用户输入
    processInput(&sm,"start");
    processInput(&sm,"invalid");
    processInput(&sm,"stop");
    return 0;
}