序言：世间万物皆为状态机，状态机在编程过程中使用的十分广泛。使用一个好的状态机类，可使程序有条理，业务逻辑清晰。在 github上有一个经典的状态机 r-lyeh v1.0.0。该状态机支持C++11，单头文件，轻量级，跨平台，支持函数对象(std :: function),可绑定函数回调，类成员函数，lambda表达式。功能非常强大，使用非常方便，是一个不错的C++类，值得推荐。https://github.com/r-lyeh-archived/fsm

 

1.简单使用

传统方式：面向过程，很大一个switch结构

switch(state){
case state0:std::cout << "进入状态0" << std::endl;break;
case state1:std::cout << "进入状态1" << std::endl;break;
case state2:std::cout << "进入状态2" << std::endl;break;
case state3:std::cout << "进入状态3" << std::endl;break;
case state4:std::cout << "进入状态4" << std::endl;break;
//......
}

使用状态机类：面向对象，思路清晰明了

#include "fsm.hpp"

fsm::stack fsm;//定义一个状态机变量

//事件绑定
fsm.on('state0', 'init') = [&]( const fsm::args &args ) {
   std::cout << "进入状态0" << std::endl;
};
fsm.on('state0', 'quit') = [&]( const fsm::args &args ) {
   std::cout << "状态0结束" << std::endl;
};

fsm.on('state1', 'init') = [&]( const fsm::args &args ) {
   std::cout << "进入状态1" << std::endl;
};
fsm.on('state1', 'quit') = [&]( const fsm::args &args ) {
   std::cout << "状态1结束" << std::endl;
};

fsm.on('state2', 'init') = [&]( const fsm::args &args ) {
   std::cout << "进入状态2" << std::endl;
};
fsm.on('state2', 'quit') = [&]( const fsm::args &args ) {
   std::cout << "状态2结束" << std::endl;
};

//......

fsm.set('state0');//进入状态state0

2.源码自带示例

先看一下源码自带的示例，了解如何使用该状态机类。

示例使用状态机实现一个小游戏，一只蚂蚁战士在家与丛林之间不断地巡逻，在某个时间蚂蚁受到敌人攻击，进入防御状态，血量持续减少，当血量为0时，恢复巡逻状态，继续巡逻。

  ╮╭
╭─╮      ╭─────╮
( 0 ）═｛  ﹝﹝﹝ ｝
╰─╯      ╰─────╯
              ╯╯    ╰╰

状态表：

| 状态名 | 事件     | function名

─────────────────
| 行走    | 初始化  | init
| 行走    | 结束     | quit 
| 行走    | 暂停     | push
| 行走    | 恢复     | back
| 行走    | 刷新     | tick
| 防御    | 初始化 | init 
| 防御    | 刷新     | tick

 

3.源码自带示例分析：

#include <iostream>

// custom states (gerunds) and actions (infinitives)

enum {
    walking = 'WALK',//走路状态，注：单引号表示不是字符串，实际是一个整形，也可设置为一个整数
    defending = 'DEFN',//防御状态
    tick = 'tick'//刷新
};

struct ant_t {
    fsm::stack fsm;
    int health, distance, flow;

    ant_t() : health(0), distance(0), flow(1) {
        // define fsm transitions: on(state,trigger) -> do lambda
        fsm.on(walking, 'init') = [&]( const fsm::args &args ) {//行走状态，绑定init函数（初始化）
            std::cout << "initializing" << std::endl;
        };
        fsm.on(walking, 'quit') = [&]( const fsm::args &args ) {//行走状态，绑定quit函数（状态结束时清理）
            std::cout << "exiting" << std::endl;
        };
        fsm.on(walking, 'push') = [&]( const fsm::args &args ) {//行走状态，绑定push函数，暂停时执行
            std::cout << "pushing current task." << std::endl;
        };
        fsm.on(walking, 'back') = [&]( const fsm::args &args ) {//行走状态，绑定back函数，恢复时执行
            std::cout << "back from another task. remaining distance: " << distance << std::endl;
        };
        fsm.on(walking, tick) = [&]( const fsm::args &args ) {//行走状态，定义一个tick动作，用于输出一些信息
            std::cout << "\r" << "\\|/-"[ distance % 4 ] << " walking " << (flow > 0 ? "-->" : "<--") << " ";
            distance += flow;
            if( 1000 == distance ) {
                std::cout << "at food!" << std::endl;
                flow = -flow;
            }
            if( -1000 == distance ) {
                std::cout << "at home!" << std::endl;
                flow = -flow;
            }
        };
        fsm.on(defending, 'init') = [&]( const fsm::args &args ) {//防御状态，绑定init函数（初始化）
            health = 1000;
            std::cout << "somebody is attacking me! he has " << health << " health points" << std::endl;
        };
        fsm.on(defending, tick) = [&]( const fsm::args &args ) {//行走状态，定义一个tick动作，用于输出一些信息
            std::cout << "\r" << "\\|/-$"[ health % 4 ] << " health: (" << health << ")   ";
            --health;
            if( health < 0 ) {
                std::cout << std::endl;
                fsm.pop();//血量小于0，结束本状态，恢复为之前的状态
            }
        };

        // set initial fsm state
        fsm.set( walking );//初始化状态为行走状态
    }
};

int main() {
    ant_t ant;//创建一个蚂蚁战士（状态机）
    for(int i = 0; i < 12000; ++i) {//满足条件时进入防御状态，战士受到攻击，攻击完成自动恢复为行走状态
        if( 0 == rand() % 10000 ) {
            ant.fsm.push(defending);
        }
        ant.fsm.command(tick);//刷新每一帧，输出一些信息
    }
}

源代码还有一个CD播放器的例子，大家自行去研究。

 

4.状态机类fsm实现原理

关键变量：std::map< bistate, fsm::call > callbacks; 实际为一个表，绑定状态和其对应事件的function

关键函数：bool call( const fsm::state &from, const fsm::state &to )， 从表中查找指定状态的指定动作对应的函数回调并执行

在stack结构中有一个表，保存的是每个状态及其所有动作对应的function（即C++11中的std :: function，可以存储，复制和调用任何可调用的目标 ：包括函数，lambda表达式，绑定表达式或其他函数对象，以及指向成员函数和指向数据成员的指针），当状态发生变化时会从表中查找到要执行的函数回调并执行。

• 每个状态机都有'init', 'quit', 'push', 'back'四个标准事件，在适当时机自动调用
• init：在进入某一状态时自动调用 ；quit在某一状态结束时自动调用 
• push：将某一状态暂停时自动调用；back：将某一状态恢复时自动调用
• 注意：每个状态的四个标准要自己实现并绑定，如果没有实现，则不调用 
• 使用set设置初始状态或改变当前状态

5.源码分析：

fsm.hpp

#pragma once

#define FSM_VERSION "1.0.0" /* (2015/11/29) Code revisited to use fourcc integers (much faster); clean ups suggested by Chang Qian
#define FSM_VERSION "0.0.0" // (2014/02/15) Initial version */

#include <algorithm>
#include <deque>
#include <functional>
#include <iostream>
#include <map>
#include <sstream>
#include <string>
#include <vector>

namespace fsm
{
    template<typename T>//模板函数，实现任意类型数据转换字符串
    inline std::string to_string( const T &t ) {
        std::stringstream ss;
        return ss << t ? ss.str() : std::string();
    }

    template<>
    inline std::string to_string( const std::string &t ) {
        return t;
    }

    typedef std::vector<std::string> args;
    typedef std::function< void( const fsm::args &args ) > call;

    struct state {//代表状态
        int name;
        fsm::args args;

        state( const int &name = 'null' ) : name(name)//使用整形初始化一个状态
        {}

        state operator()() const {//运算符重载，返回状态自己
            state self = *this;
            self.args = {};
            return self;
        }
        template<typename T0>
        state operator()( const T0 &t0 ) const {//设置状态的数据t0，并转换成字符串保存
            state self = *this;
            self.args = { fsm::to_string(t0) };
            return self;
        }
        template<typename T0, typename T1>
        state operator()( const T0 &t0, const T1 &t1 ) const {//设置状态的数据t0 t1
            state self = *this;
            self.args = { fsm::to_string(t0), fsm::to_string(t1) };
            return self;
        }

        operator int () const {
            return name;
        }

        bool operator<( const state &other ) const {
            return name < other.name;
        }
        bool operator==( const state &other ) const {
            return name == other.name;
        }

        template<typename ostream>
        inline friend ostream &operator<<( ostream &out, const state &t ) {//打印一个状态
            if( t.name >= 256 ) {
                out << char((t.name >> 24) & 0xff);
                out << char((t.name >> 16) & 0xff);
                out << char((t.name >>  8) & 0xff);
                out << char((t.name >>  0) & 0xff);
            } else {
                out << t.name;
            }
            out << "(";
            std::string sep;
            for(auto &arg : t.args ) {
                out << sep << arg;
                sep = ',';
            }
            out << ")";
            return out;
        }
    };

    typedef state trigger;

    struct transition {
        fsm::state previous, trigger, current;

        template<typename ostream>
        inline friend ostream &operator<<( ostream &out, const transition &t ) {
            out << t.previous << " -> " << t.trigger << " -> " << t.current;
            return out;
        }
    };

    class stack {//保存状态的容量
    public:

        stack( const fsm::state &start = 'null' ) : deque(1) {//使用一个状态初始化容器
            deque[0] = start;
            call( deque.back(), 'init' );//执行init函数
        }

        stack( int start ) : stack( fsm::state(start) ) 
        {}

        ~stack() {
            // ensure state destructors are called (w/ 'quit')
            while( size() ) {
                pop();//执行每个状态的qiut函数
            }
        }

        // pause current state (w/ 'push') and create a new active child (w/ 'init')
        void push( const fsm::state &state ) {//暂停一个状态
            if( deque.size() && deque.back() == state ) {
                return;
            }
            // queue
            call( deque.back(), 'push' );//执行上一个状态push函数
            deque.push_back( state );
            call( deque.back(), 'init' );//执行新状态的init函数
        }

        // terminate current state and return to parent (if any)
        void pop() {//恢复一个状态
            if( deque.size() ) {
                call( deque.back(), 'quit' );//执行当前状态的qiut函数
                deque.pop_back();
            }
            if( deque.size() ) {
                call( deque.back(), 'back' );//执行下一个状态的back函数（待恢复的状态）
            }
        }

        // set current active state
        void set( const fsm::state &state ) {//设置当前状态为state ,并自动执行相关函数
            if( deque.size() ) {
                replace( deque.back(), state );
            } else {
                push(state);
            }
        }

        // number of children (stack)
        size_t size() const {
            return deque.size();
        }

        // info
        // [] classic behaviour: "hello"[5] = undefined, "hello"[-1] = undefined
        // [] extended behaviour: "hello"[5] = h, "hello"[-1] = o, "hello"[-2] = l
        fsm::state get_state( signed pos = -1 ) const {//获取当前状态
            signed size = (signed)(deque.size());
            return size ? *( deque.begin() + (pos >= 0 ? pos % size : size - 1 + ((pos+1) % size) ) ) : fsm::state();
        }
        fsm::transition get_log( signed pos = -1 ) const {
            signed size = (signed)(log.size());
            return size ? *( log.begin() + (pos >= 0 ? pos % size : size - 1 + ((pos+1) % size) ) ) : fsm::transition();
        }
        std::string get_trigger() const {
            std::stringstream ss;
            return ss << current_trigger, ss.str();
        }

        bool is_state( const fsm::state &state ) const {
            return deque.empty() ? false : ( deque.back() == state );
        }

        /* (idle)___(trigger)__/''(hold)''''(release)''\__
        bool is_idle()      const { return transition.previous == transition.current; }
        bool is_triggered() const { return transition.previous == transition.current; }
        bool is_hold()      const { return transition.previous == transition.current; }
        bool is_released()  const { return transition.previous == transition.current; } */

        // setup
        fsm::call &on( const fsm::state &from, const fsm::state &to ) {//返回表中绑定的一个匿名函数
            return callbacks[ bistate(from,to) ];
        }

        // generic call
        bool call( const fsm::state &from, const fsm::state &to ) const {
            std::map< bistate, fsm::call >::const_iterator found = callbacks.find(bistate(from,to));
            if( found != callbacks.end() ) {
                log.push_back( { from, current_trigger, to } );
                if( log.size() > 50 ) {
                    log.pop_front();
                }
                found->second( to.args );
                return true;
            }
            return false;
        }

        // user commands
        bool command( const fsm::state &trigger ) {//执行trigger 函数
            size_t size = this->size();
            if( !size ) {
                return false;
            }
            current_trigger = fsm::state();
            std::deque< states::reverse_iterator > aborted;
            for( auto it = deque.rbegin(); it != deque.rend(); ++it ) {
                fsm::state &self = *it;
                if( !call(self,trigger) ) {
                    aborted.push_back(it);
                    continue;
                }
                for( auto it = aborted.begin(), end = aborted.end(); it != end; ++it ) {
                    call(**it, 'quit');
                    deque.erase(--(it->base()));
                }
                current_trigger = trigger;
                return true;
            }
            return false;
        }
        template<typename T>
        bool command( const fsm::state &trigger, const T &arg1 ) {
            return command( trigger(arg1) );
        }
        template<typename T, typename U>
        bool command( const fsm::state &trigger, const T &arg1, const U &arg2 ) {
            return command( trigger(arg1, arg2) );
        }

        // debug
        template<typename ostream>
        ostream &debug( ostream &out ) {
            int total = log.size();
            out << "status {" << std::endl;
            std::string sep = "\t";
            for( states::const_reverse_iterator it = deque.rbegin(), end = deque.rend(); it != end; ++it ) {
                out << sep << *it;
                sep = " -> ";
            }
            out << std::endl;
            out << "} log (" << total << " entries) {" << std::endl;
            for( int i = 0 ; i < total; ++i ) {
                out << "\t" << log[i] << std::endl;
            }
            out << "}" << std::endl;
            return out;
        }

        // aliases
        bool operator()( const fsm::state &trigger ) {//执行带参数的函数
            return command( trigger );
        }
        template<typename T>
        bool operator()( const fsm::state &trigger, const T &arg1 ) {
            return command( trigger(arg1) );
        }
        template<typename T, typename U>
        bool operator()( const fsm::state &trigger, const T &arg1, const U &arg2 ) {
            return command( trigger(arg1, arg2) );
        }
        template<typename ostream>
        inline friend ostream &operator<<( ostream &out, const stack &t ) {
            return t.debug( out ), out;
        }

    protected:

        void replace( fsm::state &current, const fsm::state &next ) {//替换某一状态
            call( current, 'quit' );
            current = next;
            call( current, 'init' );
        }

        typedef std::pair<int, int> bistate;
        std::map< bistate, fsm::call > callbacks;

        mutable std::deque< fsm::transition > log;
        std::deque< fsm::state > deque;//状态列表，最后一个为当前状态，前面的为暂停的状态
        fsm::state current_trigger;//当前状态

        typedef std::deque< fsm::state > states;
    };
}