内存动态分配与释放

[c++]代码库
#include <iostream>
using namespace std;
#include <iomanip>
//全局变量
float minsize=5;
int count1=0;
int count2=0;
#define  M  10      //假定系统允许的空闲区表最大为m
#define  N  10      //假定系统允许的最大作业数量为n
 
//已分配表的定义
struct
{
 float address;  //已分分区起始地址
 float length;   //已分分区长度，单位为字节
 int flag;          //已分配区表登记栏标志，"0"表示空栏目
}used_table[N];     //已分配区表对象名
 
//空闲区表的定义：
struct
{float address;       //空闲区起始地址
 float length;         //空闲区长度，单位为字节
 int flag;      //空闲区表登记栏标志，用"0"表示空栏目，用"1"表示未分配
}free_table[M];     //空闲区表对象名
 
//函数声明
void initialize(void);
int distribute(int, float);
int recycle(int);
void show();
 
//初始化两个表
void initialize(void)
{
      int a;
      for(a=0;a<=N-1;a++)
           used_table[a].flag=0;   //已分配表的表项全部置为空表项
        free_table[0].address=1000;
        free_table[0].length=1024;
        free_table[0].flag=1;    //空闲区表的表项全部为未分配
}
 
//最优分配算法实现的动态分区
 
int distribute(int process_name,float need_length)
{
    int i,k=-1; //k用于定位在空闲表中选择的未分配栏
    float ads,len;
    int count=0;
    i=0;
    while(i<=M-1)       //循环找到最佳的空闲分区
    {
        if(free_table[i].flag==1)
        {
            count++;
            if(count==1||free_table[i].length<free_table[k].length)
                k=i;
        }
        i=i+1;
    }
    if(k!=-1)
    {
        if((free_table[k].length-need_length)<=minsize) //整个分配
        {
            free_table[k].flag=0;
            ads=free_table[k].address;
            len=free_table[k].length;
        }
        else
        {    //切割空闲区
            ads=free_table[k].address;
            len=need_length;
            free_table[k].address+=ads;
            free_table[k].length-=len;
        }
        i=0;
        //循环寻找内存分配表中标志为空栏目的项
        while(used_table[i].flag!=0)
        {i=i+1;}
 
        if(i<=N-1)     //找到，在已分配区表中登记一个表项
        {
            used_table[i].address=ads;
            used_table[i].length=len;
            used_table[i].flag=process_name;
            count1++;
        }
        else      //已分配区表长度不足
        {
            if(free_table[k].flag==0)  //将已做的整个分配撤销
            {
                free_table[k].flag=1;
                free_table[k].address=ads;
                free_table[k].length=len;
            }
            else                            //将已做的切割分配撤销
            {
                free_table[k].address=ads;
                free_table[k].length+=len;
            }
            cout<<"内存分配区已满，分配失败！\n";
            return 0;
        }
    }
    else
    {
        cout <<"无法为该作业找到合适分区！\n";
        return 0;
    }
    return process_name;
}
 
int recycle(int process_name)
{
    int y=0;
    float recycle_address,recycle_length;
    int i,j,k;        //j栏是下邻空闲区，k栏是上栏空闲区
    int x;
   //在内存分配表中找到要回收的作业
    while(y<=N-1&&used_table[y].flag!=process_name)
    {y=y+1;}
 
    if(y<=N-1)    //找到作业后，将该栏的标志置为'0'
    {
        recycle_address=used_table[y].address;
        recycle_length=used_table[y].length;
        used_table[y].flag=0;
        count2++;
    }
    else             //未能找到作业，回收失败
    {
        cout<<"该作业不存在！\n";
        return 0;
    }
    j=k=-1;
    i=0;
    while(!(i>=M||(k!=-1&&j!=-1)))       //修改空闲分区表
    {
        if(free_table[i].flag==1)
        {
            if((used_table[y].address)==recycle_address)
                k=i;     //判断是否有上邻接
            if((used_table[y].length)==free_table[i].address)
                j=i; //判断是否有下邻接
        }
      i=i+1;
    }
      //合并空闲区
    if(k!=-1)         //回收区有上邻接
    {
        if(j!=-1){   //回收区也有下邻接，和上下邻接合并
                    free_table[k].length+=free_table[j].length+recycle_length;
                    free_table[j].flag=0;     //将第j栏的标记置为'0'
                }
        else                          //不存在下邻接，和上邻接合并
            free_table[k].length+=recycle_length;
    }
    else if(j!=-1)
    {    //只有下邻接，和下邻接合并
        free_table[j].length+=recycle_length;
        free_table[j].address=recycle_address;
    }
    else
    {                              //上下邻接都没有
        x=0;
        while(free_table[x].flag!=0)
            x=x+1; //在空闲区表中查找一个状态为'0'的栏目
        if(x<=M-1)
        { //找到后，在空闲分区中登记回收的内存
            free_table[x].address=recycle_address;
            free_table[x].length=recycle_length;
            free_table[x].flag=1;
        }
        else
        {         //空闲表已满，执行回收失败
            used_table[y].flag=process_name;
            cout<<"空闲区已满，回收失败！\n";
            return 0;
        }
      }
    return process_name;
}
 
void show()      //程序执行时输出模拟的内存分配回收表
{
    cout<<"+++++++++++++++++++++++++++++++++++++++\n";
    cout<<"+++++++       空  闲  区        +++++++\n";
    cout<<"+++++++++++++++++++++++++++++++++++++++\n";
    for(int i=0;i<=count2;i++)
        if(free_table[i].flag!=0)
            cout<<"初始地址："<<free_table[i].address<<"   "<<"长度："<<free_table[i].length<<"   "<<"状  态："<<free_table[i].flag<<endl;
    cout<<"+++++++++++++++++++++++++++++++++++++++\n";
    cout<<"+++++++       已 分 配 区        ++++++\n";
    cout<<"+++++++++++++++++++++++++++++++++++++++\n";
    for(int j=0;j<count1;j++)
        if(used_table[j].flag!=0)
            cout<<"初始地址："<<used_table[j].address<<"   "<<"长度："<<used_table[j].length<<"   "<<"作业名："<<used_table[j].flag<<endl;
}
 
 
 
int main()         //主函数调用各功能函数对所有工作进行测试
{
    int choice;       //用来选择将要进行的操作
    int job_name;
    float need_memory;
    bool exitFlag=false;
    cout<<"       动态分区分配方式的模拟       \n";
    cout<<"************************************\n";
    cout<<"请选择操作类型：\n";
    initialize(); //开创空闲区和已分配区两个表
    while(!exitFlag)
    {
        cout<<"********************************************\n";
        cout<<"**    1: 分配内存        2: 回收内存      **\n";
        cout<<"**    3: 查看分配        0: 退    出      **\n";
        cout<<"********************************************\n";
        cout<<"请输入您的操作 ：";
        cin>>choice;
           switch(choice)
           {
             case 0:exitFlag=true;                      //退出操作
                    break;
             case 1:cout<<"请输入作业号和所需内存：";
                      cin>>job_name>>need_memory;
                       if(job_name!=0&&need_memory!=0)
                        distribute(job_name, need_memory); // 分配内存
                       else if(job_name==0)
                         cout<<"作业号不能为零!\n请重新选择操作：\n";
                       else if(need_memory==0)
                         cout<<"内存分配数不能为零!\n请重新选择操作：\n";
                    break;
             case 2:int ID;
                    cout<<"请输入您要释放的作业号：";
                    cin>>ID;
                       if(ID!=0)
                            recycle(ID);             //回收内存
                       else
                            cout<<"作业名不能为零!\n请重新选择操作：\n";
                    break;
           }
    }
 
}
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