磁盘调度算法（操作系统课设作业）

FIFO：按访问请求到达的先后次序进行调度。

SSTF：优先选择使磁头臂从当前位置开始移动最少的磁盘I/O请求进行调度。

SCAN：要求磁头臂先沿一个方向移动，并在途中满足所有未完成的请求，直到它到达这个方向上的最后一个磁道，或者在这个方向上没有别的请求为止，后一种改进有时候称作LOOK策略。然后倒转服务方向，沿相反方向扫描，同样按顺序完成所有请求。

C-SCAN：在磁盘调度时，把扫描限定在一个方向，当沿某个方向访问到最后一个磁道时，磁头臂返回到磁盘的另一端，并再次开始扫描。

1、main()函数模块：初始化磁道序号和初始磁针位置并提供选择列表；

2、FIFO()函数模块：先进先出调度算法；

3、SSTF()函数模块：最短服务时间优先调度算法；

4、SCAN()函数模块：扫描（电梯）调度算法；

5、C-SCAN()函数模块：循环扫描调度算法。

#include
#include
#include
#define MAXTRACK 1000
using namespace std;

int TRACK[MAXTRACK];										//初始磁道序列 
int track[MAXTRACK];										//排序后的磁道序列 
int start;													//初始磁针位置 
int tracknumber = 0;										//磁道总数 
int location;												//初始磁针当前（下一个）位置的下标 
double length;												//总寻道长度 

void FIFO(int TRACK[], int tracknumber, int start) {
	double length = 0;
	cout<<"Initial track position:" << start << endl;
	for(int i = 0; i < tracknumber; i++) {
		length += abs(TRACK[i] - start);					//按初始顺序将长度累加 
		cout << "The track number of the next access is:" << TRACK[i] << endl;
		cout << "The length of the seek is:" << abs(TRACK[i] - start) << endl;
		start = TRACK[i];									//移动磁针位置 
	}
	cout << "The average seek length is:" << length / tracknumber << endl;
}

void SSTF(int TRACK[], int tracknumber, int start) {
	int left, right;										//left:左移"指针"；right:右移"指针" 
	bool flag;												//false:左移"指针"到达边界;true: 右移"指针"到达边界 
	length = 0;
	for(int i = 0; i < tracknumber; i++)
		track[i] = TRACK[i];
	sort(track, track + tracknumber);
	if(start >= track[tracknumber - 1]) {					//初始磁针位置比所有访问位置都大 
		for(int i = tracknumber - 1; i >= 0; i--) {
			length += start - track[i];
			cout << "The track number of the next access is:" << track[i] << endl;
			cout << "The length of the seek is:" << abs(track[i] - start) << endl;
			start = track[i];
		}
	}
	else if(start <= track[0]) {							//初始磁针位置比所有访问位置都小 
		for(int i = 0; i < tracknumber; i++) {
			length += track[i] - start;
			cout << "The track number of the next access is:" << track[i] << endl;
			cout << "The length of the seek is:" << abs(track[i] - start) << endl;
			start = track[i];
		}
	}
	else {													//初始磁针位置在访问区域中 
		for(int i = 1; i < tracknumber; i++)
			if(start > track[i - 1] && start <= track[i])
				location = i;								//定位磁针 
		left = location - 1;
		right = location;
		while(true) {
			if(abs(start - track[left]) >= abs(start - track[right])) {
				length += abs(start - track[right]);		//右侧更近 
				cout << "The track number of the next access is:" << track[right] << endl;
				cout << "The length of the seek is:" << abs(track[right] - start) << endl;
				start = track[right];
				if(right == tracknumber - 1) {				//到达右边界 
					flag = true;
					break;
				}
				right++;
			}
			else {											
				length += abs(start - track[left]);			//左侧更近 
				cout << "The track number of the next access is:" << track[left] << endl;
				cout << "The length of the seek is:" << abs(track[left] - start) << endl;
				start = track[left];
				if(left == 0) {								//到达左边界 
					flag = false;
					break;
				}
				left--;
			}
		}
		if(flag) {											//左移"指针"一直左移 
			while(true) {
				if(left == 0) {	
					length += abs(start - track[left]);
					cout << "The track number of the next access is:" << track[left] << endl;
					cout << "The length of the seek is:" << abs(track[left] - start) << endl;
					break;
				}
				else {
					length += abs(start - track[left]);
					cout << "The track number of the next access is:" << track[left] << endl;
					cout << "The length of the seek is:" << abs(track[left] - start) << endl;
					start = track[left--];
				}  
			} 
		}
		else {												//右移"指针"一直右移 
			while(true) {
				if(right == tracknumber-1) {	
					length += abs(start - track[right]);
					cout << "The track number of the next access is:" << track[right] << endl;
					cout << "The length of the seek is:" << abs(track[right] - start) << endl;
					break;
				}
				else {
					length += abs(start - track[right]);
					cout << "The track number of the next access is:" << track[right] << endl;
					cout << "The length of the seek is:" << abs(track[right] - start) << endl;
					start = track[right++];
				}  
			} 
		}
	}
	cout << "The average seek length is:" << length / tracknumber << endl;
}

void SCAN(int TRACK[], int tracknumber, int start) {
	bool flag;												//false:优先向左移动;true:优先向右移动 
	length = 0;
	for(int i = 0; i < tracknumber; i++)
		track[i] = TRACK[i];
	sort(track, track + tracknumber);
	for(int i = 1; i < tracknumber; i++) {
		if(start > track[i - 1] && start <= track[i]) {
			location = i;									//定位磁针 
			if(abs(track[i] - start) > abs(track[i - 1] - start)) flag = false;
			else flag = true;
			break;											//确定磁针距离最近的两端磁道中更近的磁道所在方向 
		}
	}
	if(!flag) {												//先左移 
		for(int i = location - 1; i >= 0; i--) {
			length += abs(start - track[i]);
			cout << "The track number of the next access is:" << track[i] << endl;
			cout << "The length of the seek is:" << abs(track[i] - start) << endl;
			start = track[i];
		}
		for(int i = location; i < tracknumber; i++) {		//调转方向 
			length += abs(start - track[i]);
			cout << "The track number of the next access is:" << track[i] << endl;
			cout << "The length of the seek is:" << abs(track[i] - start) << endl;
			start = track[i];
		}
	}
	else {													//先右移 
		for(int i = location; i < tracknumber; i++) {
			length += abs(start - track[i]);
			cout << "The track number of the next access is:" << track[i] << endl;
			cout << "The length of the seek is:" << abs(track[i] - start) << endl;
			start = track[i];
		}
		for(int i = location - 1; i >= 0; i--) {			//调转方向
			length += abs(start-track[i]);
			cout << "The track number of the next access is:" << track[i] << endl;
			cout << "The length of the seek is:" << abs(track[i] - start) << endl;
			start = track[i];
		}
	}
	cout << "The average seek length is:" << length / tracknumber << endl;
}

void C_SCAN(int TRACK[], int tracknumber, int start) {
	bool flag;												//false:优先向左移动;true:优先向右移动 
	length = 0;
	for(int i = 0; i < tracknumber; i++)
		track[i] = TRACK[i];
	sort(track, track + tracknumber);
	for(int i = 1; i < tracknumber; i++) {
		if(start > track[i - 1] && start <= track[i]) {
			location = i;									//定位磁针
			if(abs(track[i] - start) > abs(track[i - 1] - start)) flag = false;
			else flag = true;
			break;											//确定磁针距离最近的两端磁道中更近的磁道所在方向
		}
	}
	if(!flag) {												//先左移
		for(int i = location - 1; i >= 0; i--) {
			length += abs(start - track[i]);
			cout << "The track number of the next access is:" << track[i] << endl;
			cout << "The length of the seek is:" << abs(track[i] - start) << endl;
			start = track[i];
		}
		for(int i = tracknumber - 1 ; i >= location ; i--) {//从另一端继续 
			length += abs(start - track[i]);
			cout << "The track number of the next access is:" << track[i] << endl;
			cout << "The length of the seek is:" << abs(track[i] - start) << endl;
			start = track[i];
		}
	}
	else {													//先右移
		for(int i = location; i < tracknumber; i++) {
			length += abs(start - track[i]);
			cout << "The track number of the next access is:" << track[i] << endl;
			cout << "The length of the seek is:" << abs(track[i] - start) << endl;
			start = track[i];
		}
		for(int i = 0; i <= location - 1; i++) {			//从另一端继续
			length += abs(start-track[i]);
			cout << "The track number of the next access is:" << track[i] << endl;
			cout << "The length of the seek is:" << abs(track[i] - start) << endl;
			start = track[i];
		}
	}
	cout << "The average seek length is:" << length / tracknumber << endl;
}

int main(void) {
	int choice;
	cout << "****************磁盘调度算法****************" << endl;
	cout << "Please enter the track number to access (1-1000, enter -1 to stop input):" << endl;
	while (true) {											//输入访问的磁道序号 
		cin >> TRACK[tracknumber];
		if (TRACK[tracknumber] == -1)
			break;
		else if(TRACK[tracknumber] > MAXTRACK || TRACK[tracknumber] < 0) {
			cout << "Input error, please re-enter:" << endl;
			continue;
		}
		tracknumber++;
	}
	for(int i = 0; i < tracknumber; i++)
		track[i] = TRACK[i];
	sort(track, track + tracknumber);
	cout<<"Please enter the initial position of the magnetic needle : ";
	cin >> start;											//输入初始磁针位置 
	while(true) {
		if(start < 0 || start > MAXTRACK) {
			cout << "Input error, please re-enter:";
			cin >> start;
		}
		else
			break;
	}
	cout << "There are currently " << tracknumber << " tracks to access." << endl;
	cout << "The sequence of the input track is:";
	for(int i = 0; i < tracknumber; i++) {
		if(i != tracknumber - 1)
			cout << TRACK[i] << "->";
		else
			cout << TRACK[i] << endl;
	}
	cout << "The sorted track sequence is:";
	for(int i = 0; i < tracknumber; i++) {
		if(i != tracknumber - 1)
			cout << track[i] << "->";
		else
			cout << track[i] << endl;
	}
	cout << "The initial position of the magnetic needle:" << start << endl;
	while(true) {
		cout << "1.FIFO" << endl;
		cout << "2.SSTF" << endl;
		cout << "3.SCAN" << endl;
		cout << "4.C-SCAN" << endl;
		cout << "Please select disk scheduling algorithm (Enter 0 to exit the program):";
		cin >> choice;
		if(choice >= 0 && choice <= 4) {
			switch(choice) {
				case 0:
					exit(0);
				case 1:
					FIFO(TRACK, tracknumber, start);
					break;
				case 2:
					SSTF(TRACK, tracknumber, start);
					break;
				case 3:
					SCAN(TRACK, tracknumber, start);
					break;
				case 4:
					C_SCAN(TRACK, tracknumber, start);
					break;
			}
		}
		else
			cout << "Input error, please re-enter!" << endl;
	}
}