《C現代編程》第四章 C語言與設計模式

 當狀態位有三種以上，我們用面向對象的狀態設置；

下面是現代編程 ，CD 播放機的狀態設置；

State.h

#ifndef _STATE_H 
#define _STATE_H 

#include <stddef.h>
#include <stdio.h>
#ifdef _cplusplus
extren "C"
{
#endif

	typedef struct State
	{
		const struct State *(* const stop)(const struct State *pThis);
		const struct State *(* const playOrPause)(const struct State *pThis);
	}State;

	static const State *pCurrentState;

	void initialize();
	void onStop();
	void onPlayOrPause();

	const State *ignore(const State *pThis);
	const State *startPlay(const State *pThis);
	const State *stopPlay(const State *pThis);
	const State *pausePlay(const State *pThis);
	const State *resumePlay(const State *pThis);

	static const State IDlE = { ignore, startPlay};
	static const State PLAY = {stopPlay , pausePlay};
	static const State PAUSE = {stopPlay , resumePlay};


#ifdef _cplusplus
}
#endif
#endif

State.cpp

#include "State.h"
#include <stdio.h>
static unsigned int count = 0;
void initialize()
{
	pCurrentState = &IDlE;
}

void onStop()
{
	pCurrentState = pCurrentState->stop(pCurrentState);
}

void onPlayOrPause()
{
	pCurrentState = pCurrentState->playOrPause(pCurrentState);
}

static const State *ignore(const State *pThis)
{
	printf("[%d] %s\n",++count,"ignore");
	return pCurrentState;
}

static const State *startPlay(const State *pThis)
{
	printf("[%d] %s\n", ++count, "startPlay");
	return &PLAY;
}

static const State *stopPlay(const State *pThis)
{
	printf("[%d] %s\n", ++count, "stopPlay");
	return &IDlE;
}

static const State *pausePlay(const State *pThis)
{
	printf("[%d] %s\n", ++count, "pausePlay");
	return &PAUSE;
}

static const State *resumePlay(const State *pThis)
{
	printf("[%d] %s\n", ++count, "resumePlay");
	return &PLAY;
}

main.cpp

#include "State.h"
#include <stdio.h>
int main()
{
	initialize();
	printf("--------------\n");
	onPlayOrPause();//開始
	printf("--------------\n");
	onPlayOrPause();//暫停
	printf("--------------\n");
	onPlayOrPause();//繼續
	printf("--------------\n");
	onPlayOrPause();//暫停
	printf("--------------\n");
	onPlayOrPause();//繼續
	printf("--------------\n");
	onStop();

	return 0;
}

運行結果

 它的狀態圖