zhucunfenpeiyuhuishou.cpp

实现模拟操作系统运行时的主存空间的分配与回收

#include<stdio.h>
#include<malloc.h>
typedef struct freechain
{
	int startadd;//起始地址
	int state;//空闲区状态,0表示空闲,1表示被分配
	int blocksize;//空间大小
	struct freechain *front,*behind;//front指向下一个,behind指向上一个
}freechains;
freechains *head;
int n;
void output()
{
	struct freechain *p;
	p=head->front;
	printf("起始地址       大小       状态\n");
	do
	{
		printf("%d	       %-6d",p->startadd,p->blocksize);
		if(p->state==0)
			printf("     未分配\n");
		else
			printf("     已分配\n");
		p=p->front;
	}while(p!=NULL);
}
void alloc(struct freechain *m)//内存分配函数
{
	int i,j=0,size,a,b;
	m=head->front;
	printf("输入需要分配内存的大小:");
	scanf("%d",&size);
	for(i=0;i<n;i++)
	{
		if(m->blocksize>=size)
		{
			j=1;
			break;
		}
		else
			m=m->front;
	}
	if(j==0)
		printf("no comfortable place can be distribute!!!\n");
	else if(m->blocksize>size)
	{
		a=m->blocksize;
		b=m->startadd;
		m->state=1;
		m->blocksize=size;
		m->startadd=m->startadd+a-size;
		printf("分配后的内存状态为:\n");
		output();
		m->startadd=b;
		m->blocksize=a-size;
		m->state=0;
		printf("分配后的空闲内存状态为:\n");
		output();
	}
	else if(m->blocksize==size)
	{
		n--;
		if(m->front==NULL&&m->behind==NULL)
		{
			m->state=1;
			output();
			printf("this chain is empty\n");
		}
		else if(m->behind==NULL)
		{
			m->state=1;
			printf("分配后的内存状态为\n");
			output();
			head=m->front;
			head->behind=NULL;
			free(m);
			printf("分配后的空闲内存状态为:\n");
			output();
		}
		else if(m->front==NULL)
		{
			m->state=1; 
			printf("分配后的内存块链为:\n");
			output();
			m->behind->front=NULL;
			free(m);
			printf("分配后的空闲内存状态为:\n");
			output();
		}
		else
		{
			m->state=1;
			printf("分配后的内存块链为:\n");
			output();
			m->front->behind=m->behind;
			m->behind->front=m->front;
			free(m);
			printf("分配后的空闲内存状态为:\n");
			output();
		}
		n++;
	}
}
void release(struct freechain *p)//回收函数
{
	int i, j=0;
	freechains *newnode,*freenode;
	p=head->front;
	newnode=(struct freechain *)malloc(sizeof(struct freechain));
	printf("请输入需要回收内存块的首地址和长度!\n");
	printf("起始地址:");
	scanf("%d",&newnode->startadd);
	printf("空间大小");
	scanf("%d",&newnode->blocksize);
	newnode->front=newnode->behind=NULL;
	newnode->state=0;
	for(i=0;i<n;i++)
	{
		if(p->startadd+p->blocksize==newnode->startadd||p->startadd
		==newnode->startadd+newnode->blocksize) 
		{
			j=1;
			break;
		}
		else
			p=p->front;
	}
	if(j==0)
	{
		p=head->front;
		while(p->startadd<newnode->startadd&&p->front!=NULL)
		{
			p=p->front;
		}
		if(n==1&&newnode->startadd<p->startadd)
		{
			newnode->front=p;
			p->behind=newnode;
			head->front=newnode;
			printf("回收后的空间内存块链:\n");
			output();
		}
		else
		{
			if(p->startadd>newnode->startadd&&p->behind==NULL)
			{
				newnode->front=p;
				p->behind=newnode;
				head->front=newnode;
				newnode->behind=NULL;
				printf("回收后的空间内存块链:\n");
				output();
			}
			else if(p->startadd<newnode->startadd&&p->front==NULL)
			{
				p->front=newnode;
				newnode->front=NULL;
				newnode->behind=p;
				printf("回收后的空间内存块链:\n");
				output();
			}
			else if(p->startadd>newnode->startadd&&p->behind)
			{
				p->behind->front=newnode;
				newnode->front=p;
				newnode->behind=p->behind;
				printf("回收后的空间内存块链:\n");
				output();
			}
			else if(p->startadd<newnode->startadd&&p->front)
			{
				p->front->behind=newnode;
				newnode->front=p->front;
				newnode->behind=p;
				printf("回收后的空间内存块链:\n");
				output();
			}
		}
	}
	else
	{	
		if(p->front!=NULL&&p->startadd+p->blocksize+newnode->blocksize
		==p->front->startadd)
		{	
			if(p->front!=NULL)
			{
				freenode=p->front;
				if(freenode->front!=NULL)
				{
					p->blocksize=p->blocksize+newnode->blocksize+p->front->blocksize;
					p->front->front->behind=p;
					p->front=(p->front->front);
					printf("回收后的空间内存块链:\n");
					output();
					free(freenode);
				}
				else
				{	
					freenode=p->front;
					p->blocksize=p->blocksize+newnode->blocksize+p->front->blocksize;
					p->front=NULL;
					printf("回收后的空间内存块链:\n");
					output();
					free(freenode);
				}
			}
		}
		else if(p->startadd==newnode->startadd+newnode->blocksize)
		{
			p->startadd=newnode->startadd;
			p->blocksize+=newnode->blocksize;
			printf("回收后的空间内存块链:\n");
			output();
		}
		else
		{
			p->blocksize+=newnode->blocksize;
			printf("回收后的空间内存块链:\n");
			output();
		}
	}
}
int main()
{
	int i;
	struct freechain *p,*q;
	head=(struct freechain *)malloc(sizeof(struct freechain));
	printf("请输入空闲的内存块个数:");
	scanf("%d",&n);
	if(n<1)
	{
		printf("error input!!!\n");
		goto end;
	}
	else
	{
		head->front=(struct freechain *)malloc(sizeof(struct freechain));
		printf("请输入空闲内存的信息!!!\n");
		p=head->front;
		p->state=0;p->behind=NULL;
		printf("起始地址:");
		scanf("%d",&p->startadd);
		printf("空间大小:");
		scanf("%d",&p->blocksize);
		if(n==1)
		{			
			p->front=NULL;
			p->state=0;
		}
		else
		{
			for(i=1;i<n;i++)
			{
				p->front=(struct freechain *)malloc(sizeof(struct freechain));
				q=p->front;
				q->state=0;
				q->behind=p;
				printf("起始地址:");
				scanf("%d",&q->startadd);
				printf("空间大小:");
				scanf("%d",&q->blocksize);
				p=p->front;
			}
			q->front=NULL;
		}
	}
	alloc(p);
	release(p);
end:return 0;
}