内存分配_sbrk,brk

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写在前面：小生纯业余选手，开此博仅仅是为了积累，纯当笔记来用。如有看官光临小生博客，请不要相信我的代码就是正确的。如果您发现了错误也恳请耽误您一点时间，请您在下面指出来，不胜感激！

如果发现一些笔记的说法完全是错误的请建议我删除！

在malloc的底层有sbrk,brk两个函数

sbrk,brk用来分配和释放内存

sbrk返回没有被映射的虚拟地址的首地址，通常sbrk与brk配合使用，用sbrk(0)获取未被映射的首地址，用brk分配所需要的内存的大小！(以后补图)

示例代码，每一段注释代码说明一点问题

#include<iostream>#include<unistd.h>#include<stdio.h>using namespace std;int main(){    /*    cout << "pid = "<< getpid()<<endl;    int *p = static_cast<int*>(sbrk(0));    *p = 4;    */        /*    int *p = static_cast<int*>(sbrk(sizeof(int)));    *p = 4;    printf("%d\n",*p);    printf("%p\n",p);    */        /*    int *pp = static_cast<int*>(sbrk(0));    brk(pp+4000);    *(pp+4) = 4;    printf("%d\n",*pp);    printf("%d\n",*(pp+4));    printf("%d\n",*(pp+5));    printf("%d\n",*(pp+4000));    printf("%d\n",*(pp+8001));    */        /*    int *p = static_cast<int*>(sbrk(0));    int *p1 = static_cast<int*>(sbrk(4));    int *p2 = static_cast<int*>(sbrk(4));    int *p3 = static_cast<int*>(sbrk(4));    int *p4 = static_cast<int*>(sbrk(4));    int *p5 = static_cast<int*>(sbrk(4));    int *p200 = static_cast<int*>(sbrk(200));    int *p201 = static_cast<int*>(sbrk(4));    int *t = static_cast<int*>(sbrk(0));    cout << "p1 = "<<p1<<endl;    cout << "p2 = "<<p2<<endl;    cout << "p3 = "<<p3<<endl;    cout << "p4 = "<<p4<<endl;    cout << "p5 = "<<p5<<endl;    cout << "p200 = "<<p200<<endl;    cout << "p201 = "<<p201<<endl;    cout << "t = "<< t <<endl;    cout << "pid = "<< getpid()<<endl;    int *tt = t;    *tt = 88;    brk(tt+4000);    *(tt+4000) = 99;    cout << "*tt = "<<*tt<<",*(tt+1) = "<<*(tt+4000)<<endl;    */        /*    int *p = static_cast<int*>(sbrk(0));    int *q = p;    for(int i = 1;i < 10;i++)    {        brk(q+1);        *q = i;        q = static_cast<int*>(sbrk(0));    }        q = p;    int *r = static_cast<int*>(sbrk(0));    while(q != r)    {        printf("%d\n",*q);        q++;    }        for(int i = 0;i<10;i++)    {        brk(r-1);    }    */        /*    int *p = static_cast<int*>(sbrk(0));    brk(p+1);    *p = 4;    printf("*p=%d\n",*p);    brk(p);    *p = 0;    printf("*P=%d\n",*p);    */    while(1);        return 0;}

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