首次适应算法，下次适应算法，最佳适应算法，最坏适应算法

[c++]代码库

#include<iostream>
#include<stdlib.h>
 
using namespace std;
 
#define Free 0 //空闲状态
#define Busy 1 //已用状态
#define OK 1    //完成
#define ERROR 0 //出错
#define MAX_length 640 //最大内存空间为640KB
typedef int Status;
int flag;
 
typedef struct freearea//定义一个空闲区说明表结构
{
    long size;   //分区大小
    long address; //分区地址
    int state;   //状态
}ElemType;
 
// 线性表的双向链表存储结构
typedef struct DuLNode
{
    ElemType data; 
    struct DuLNode *prior; //前趋指针
    struct DuLNode *next;  //后继指针
}
 
DuLNode,*DuLinkList; 
DuLinkList block_first; //头结点
DuLinkList block_last;  //尾结点
Status alloc(int);//内存分配
Status free(int); //内存回收
Status First_fit(int);//首次适应算法
Status Best_fit(int); //最佳适应算法
Status Worst_fit(int); //最差适应算法
void show();//查看分配
Status Initblock();//开创空间表 
 
Status Initblock()//开创带头结点的内存空间链表
{
    block_first=(DuLinkList)malloc(sizeof(DuLNode));
    block_last=(DuLinkList)malloc(sizeof(DuLNode));
    block_first->prior=NULL;
    block_first->next=block_last;
    block_last->prior=block_first;
    block_last->next=NULL;
    block_last->data.address=0;
    block_last->data.size=MAX_length;
    block_last->data.state=Free;
    return OK;
}
  
//分配主存
Status alloc(int ch)
{
    int request = 0;
    cout<<"请输入需要分配的主存大小(单位:KB)："; 
    cin>>request;
    if(request<0 ||request==0) 
    {
        cout<<"分配大小不合适，请重试！"<<endl;
        return ERROR;
    }
  
    if(ch==2) //选择最佳适应算法
    {
        if(Best_fit(request)==OK) cout<<"分配成功！"<<endl;
        else cout<<"内存不足，分配失败！"<<endl;
        return OK;
    }
    if(ch==3) //选择最差适应算法
    {
        if(Worst_fit(request)==OK) cout<<"分配成功！"<<endl;
        else cout<<"内存不足，分配失败！"<<endl;
        return OK;
    }
    else //默认首次适应算法
    {
        if(First_fit(request)==OK) cout<<"分配成功！"<<endl;
        else cout<<"内存不足，分配失败！"<<endl;
        return OK;
    }
}
 
//首次适应算法
Status First_fit(int request)
{
    //为申请作业开辟新空间且初始化
    DuLinkList temp=(DuLinkList)malloc(sizeof(DuLNode)); 
    temp->data.size=request;
    temp->data.state=Busy;
  
    DuLNode *p=block_first->next;
    while(p)
    {
        if(p->data.state==Free && p->data.size==request)
        {//有大小恰好合适的空闲块
            p->data.state=Busy;
            return OK;
            break;
        }
        if(p->data.state==Free && p->data.size>request)
        {//有空闲块能满足需求且有剩余
            temp->prior=p->prior;
            temp->next=p;
            temp->data.address=p->data.address;
            p->prior->next=temp; 
            p->prior=temp;
            p->data.address=temp->data.address+temp->data.size;
            p->data.size-=request;
            return OK;
            break;
        }
        p=p->next;
    }
    return ERROR;
}
 
//最佳适应算法
Status Best_fit(int request)
{
    int ch; //记录最小剩余空间
    DuLinkList temp=(DuLinkList)malloc(sizeof(DuLNode)); 
    temp->data.size=request;
    temp->data.state=Busy;
    DuLNode *p=block_first->next;
    DuLNode *q=NULL; //记录最佳插入位置
 
    while(p) //初始化最小空间和最佳位置
    {
        if(p->data.state==Free && (p->data.size>=request) )
        {
            if(q==NULL)
            {
                q=p;
                ch=p->data.size-request;
            }
            else if(q->data.size > p->data.size)
            {
                q=p;
                ch=p->data.size-request;
            }
        }
        p=p->next;
    }
 
    if(q==NULL) return ERROR;//没有找到空闲块
    else if(q->data.size==request)
    {
        q->data.state=Busy;
        return OK;
    }
    else
    {
        temp->prior=q->prior;
        temp->next=q;
        temp->data.address=q->data.address;
        q->prior->next=temp;
        q->prior=temp;
        q->data.address+=request;
        q->data.size=ch;
        return OK;
    }
    return OK;
}
  
//最差适应算法
Status Worst_fit(int request)
{
    int ch; //记录最大剩余空间
    DuLinkList temp=(DuLinkList)malloc(sizeof(DuLNode)); 
    temp->data.size=request;
    temp->data.state=Busy;
    DuLNode *p=block_first->next;
    DuLNode *q=NULL; //记录最佳插入位置
 
    while(p) //初始化最大空间和最佳位置
    {
        if(p->data.state==Free && (p->data.size>=request) )
        {
            if(q==NULL)
            {
                q=p;
                ch=p->data.size-request;
            }
            else if(q->data.size < p->data.size)
            {
                q=p;
                ch=p->data.size-request;
            }
        }
        p=p->next;
    }
 
    if(q==NULL) return ERROR;//没有找到空闲块
    else if(q->data.size==request)
    {
        q->data.state=Busy;
        return OK;
    }
    else
    {
        temp->prior=q->prior;
        temp->next=q;
        temp->data.address=q->data.address;
        q->prior->next=temp;
        q->prior=temp;
        q->data.address+=request;
        q->data.size=ch;
        return OK;
    }
    return OK;
}
 
//主存回收
Status free(int flag)
{
    DuLNode *p=block_first;
    for(int i= 0; i <= flag; i++)
        if(p!=NULL)
            p=p->next;
        else
            return ERROR;
 
    p->data.state=Free;
    if(p->prior!=block_first && p->prior->data.state==Free)//与前面的空闲块相连
    {
        p->prior->data.size+=p->data.size;
        p->prior->next=p->next;
        p->next->prior=p->prior;
        p=p->prior;
    }
    if(p->next!=block_last && p->next->data.state==Free)//与后面的空闲块相连
    {
        p->data.size+=p->next->data.size;
        p->next->next->prior=p;
        p->next=p->next->next; 
    }
    if(p->next==block_last && p->next->data.state==Free)//与最后的空闲块相连
    {
        p->data.size+=p->next->data.size;
        p->next=NULL; 
    }
 
    return OK;
}
  
//显示主存分配情况
void show()
{
    int flag = 0;
    cout<<"\n主存分配情况:\n";
    cout<<"++++++++++++++++++++++++++++++++++++++++++++++\n\n";
    DuLNode *p=block_first->next;
    cout<<"分区号\t起始地址\t分区大小\t状态\n\n";
    while(p)
    {
        cout<<"  "<<flag++<<"\t";
        cout<<"  "<<p->data.address<<"\t\t";
        cout<<" "<<p->data.size<<"KB\t\t";
        if(p->data.state==Free) cout<<"空闲\n\n";
        else cout<<"已分配\n\n";
        p=p->next;
    }
    cout<<"++++++++++++++++++++++++++++++++++++++++++++++\n\n";
}
  
//主函数
 int  main()
{
    int ch;//算法选择标记
    cout<<"请输入所使用的内存分配算法：\n";
    cout<<"(1)首次适应算法\n(2)最佳适应算法\n(3)最差适应算法\n";
 
    cin>>ch;
    while(ch<1||ch>3)
    {
        cout<<"输入错误，请重新输入所使用的内存分配算法：\n";
        cin>>ch;
    }
 
    Initblock(); //开创空间表
    int choice;  //操作选择标记
 
    while(1)
    {
        show();
        cout<<"请输入您的操作：";
        cout<<"\n1: 分配内存\n2: 回收内存\n0: 退出\n";
         
        cin>>choice;
        if(choice==1) alloc(ch); // 分配内存
        else if(choice==2)  // 内存回收
        {
            int flag;
            cout<<"请输入您要释放的分区号：";
            cin>>flag;
            free(flag);
        }
        else if(choice==0) break; //退出
        else //输入操作有误
        {
            cout<<"输入有误，请重试！"<<endl;
            continue;
        }
    }
}

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