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C++ delete之靜態(tài)變量問題詳解

更新時(shí)間：2021年09月24日 16:27:02 作者：weixin_43436587

這篇文章主要為大家詳細(xì)介紹了C++delete的一些問題，學(xué)習(xí)如何動態(tài)創(chuàng)建對象，動態(tài)創(chuàng)建的對象與一般對象的區(qū)別，動態(tài)創(chuàng)建的對象的初始化以及釋放動態(tài)分配的內(nèi)存等知識點(diǎn)，感興趣的朋友可以參考一下

delete釋放的指針，再訪問

例1

#include <iostream>
using namespace std;
class Box
{
public:
    Box(int,int);
    ~Box();
    void volume();
    static int height;
    int width;
    int length;
};
Box::Box(int wi, int le)
{
    width = wi;
    length = le;
}
Box::~Box(){cout<<"the pointer is released."<<endl;}
void Box::volume()
{
    cout<<height*width*length<<endl;
}
int Box::height = 100;
int main()
{
    Box* p = new Box(10,20);
    delete p;
    cout<<p->height<<endl;
    cout<<Box::height<<endl;
    cout<<"width" <<p->width<<endl;
    cout<<"length "<<p->length<<endl;
    p->volume();
    return 0;
}

//輸出：
/*100
100
width 16257288
length 16253120
-1812113408*/

例2

#include <iostream>
using namespace std;
int * func(){
    int * a = new int(10);
    return a;
}
int main(){
    int * p = func();
    cout << *p << endl;//10
    //delete關(guān)鍵字用來釋放堆區(qū)數(shù)據(jù)
    delete p;
//    p = new int(5);
    cout << *p << endl;//10
    return 0;
}

//輸出
// 10
// 16584968

解釋：

訪問 delete 之后的內(nèi)存是一個(gè)未定義行為。未定義行為可能產(chǎn)生任何結(jié)果，包括但不限于：產(chǎn)生期望的結(jié)果，產(chǎn)生未期望的結(jié)果，產(chǎn)生隨機(jī)的結(jié)果，產(chǎn)生無法解釋的結(jié)果，運(yùn)行錯(cuò)誤，隨機(jī)的運(yùn)行時(shí)錯(cuò)誤，編譯錯(cuò)誤，等等 ---- 你只是放棄了對這片內(nèi)存的所有權(quán)。獲得所有權(quán)的人對這片內(nèi)存做什么（或者說什么都不做）都不關(guān)你的事

static 變量的儲存區(qū)域

https://blog.csdn.net/qq_32900237/article/details/107094377?utm_medium=distribute.pc_relevant.none-task-blog-2~default~baidujs_title~default-0.no_search_link&spm=1001.2101.3001.4242參考文章

例1

#include <iostream>
using namespace std;
class Box
{
public:
    Box(int,int);
    ~Box();
    void volume();
    static int height;
    int width;
    int length;
};
Box::Box(int wi, int le)
{
    width = wi;
    length = le;
}
Box::~Box(){cout<<"width: "<< width <<"the pointer is released."<<endl;}
void Box::volume()
{
    cout<<height*width*length<<endl;
}
int Box::height = 100;
int main()
{
    Box* p = new Box(10,20);
    cout<<"point  "<<p<<endl;  //point  0xe91470
    cout<<&(p->height)<<endl;  //0x405004
    cout<<&(p->width)<<endl;   //0xe91470
    cout<<&(p->length)<<endl;  //0xe91474
    cout<<sizeof(p)<<endl;    //4
    cout<<sizeof(*p)<<endl;   //8
    cout<<sizeof(Box)<<endl;  //8
	//delete p;              //width: 10the pointer is released.  用new創(chuàng)建的對象，必須自己用delete回收，不然系統(tǒng)不會幫助回收，出現(xiàn)內(nèi)存泄漏
    Box a = Box(1,2);
    Box *pa = &a;
    cout<<"point  "<<pa<<endl;  //point  0x61ff00
    cout<<&(pa->height)<<endl;  //0x405004
    cout<<&(pa->width)<<endl;   //0x61fefc
    cout<<&(pa->length)<<endl;  //0x61ff00
    cout<<sizeof(pa)<<endl;     //4
    cout<<sizeof(*pa)<<endl;    //8
    cout<<sizeof(a)<<endl;      //8
    Box b = Box(3,4);
    Box *pb = &b;
    cout<<"point  "<<pb<<endl;  //point  0x61fef4
    cout<<&(pb->height)<<endl;  //0x61fef4
    cout<<&(pb->width)<<endl;   //0x61fef4
    cout<<&(pb->length)<<endl;  //0x61fef8
    cout<<sizeof(pb)<<endl;
    cout<<sizeof(*pb)<<endl;
    return 0;
}
/*
point  0xe91470       新對象的地址
0x405004              靜態(tài)變量和普通變量地址不連續(xù)，是靜態(tài)變量存在數(shù)據(jù)段
0xe91470              普通變量存在 開辟的堆上
0xe91474
4                    指針大小
8                    對象所占內(nèi)存大小
8                    類大小
point  0x61fefc      新對象a的地址
0x405004             靜態(tài)變量地址不變，靜態(tài)變量屬于整個(gè)類
0x61fefc             屬于局部變量，普通變量存在 棧空間上
0x61ff00
4
8
8
point  0x61fef4     新對象b的地址， b與a之間相差8個(gè)字節(jié)
0x405004            靜態(tài)變量地址不變，靜態(tài)變量屬于整個(gè)類
0x61fef4            屬于局部變量，普通變量存在 棧空間上，地址連續(xù)
0x61fef8
4
8
width: 3the pointer is released.   自動調(diào)用析構(gòu)函數(shù)
width: 1the pointer is released.   自動調(diào)用析構(gòu)函數(shù)
*/

例2 幫助理解

#include <iostream>
using namespace std;
class Box
{
public:
    Box(int,int);
    ~Box();
    void volume();
    static int height;
    int width;
    int length;
};
Box::Box(int wi, int le)
{
    width = wi;
    length = le;
}
Box::~Box(){cout<<"width: "<< width <<"the pointer is released."<<endl;}
void Box::volume()
{
    cout<<height*width*length<<endl;
}
int Box::height = 100;
int main()
{
    Box* p = new Box(10,20);
    cout<<"point  "<<p<<endl;
    cout<<&(p->height)<<endl;
    cout<<&(p->width)<<endl;
    cout<<&(p->length)<<endl;
    cout<<sizeof(p)<<endl;
    cout<<sizeof(*p)<<endl;
    cout<<sizeof(Box)<<endl;
    // delete p;
    Box* p1 = new Box(30,40);
    cout<<"point  "<<p1<<endl;
    cout<<&(p1->height)<<endl;
    cout<<&(p1->width)<<endl;
    cout<<&(p1->length)<<endl;
    cout<<sizeof(p1)<<endl;
    cout<<sizeof(*p1)<<endl;
    cout<<sizeof(Box)<<endl;
    delete p;
    delete p1;
    Box a = Box(1,2);
    Box *pa = &a;
    cout<<"point  "<<pa<<endl;
    cout<<&(pa->height)<<endl;
    cout<<&(pa->width)<<endl;
    cout<<&(pa->length)<<endl;
    cout<<sizeof(pa)<<endl;
    cout<<sizeof(*pa)<<endl;
    cout<<sizeof(a)<<endl;
    Box b = Box(3,4);
    Box *pb = &b;
    cout<<"point  "<<pb<<endl;
    cout<<&(pb->height)<<endl;
    cout<<&(pb->width)<<endl;
    cout<<&(pb->length)<<endl;
    cout<<sizeof(pb)<<endl;
    cout<<sizeof(*pb)<<endl;
    return 0;
}
/*
point  0x791470
0x405004       
0x791470       
0x791474       
4
8
8
point  0x791108
0x405004       
0x791108       
0x79110c       
4
8
8
width: 10the pointer is released.
width: 30the pointer is released.
point  0x61fef8
0x405004
0x61fef8
0x61fefc
4
8
8
point  0x61fef0
0x405004
0x61fef0
0x61fef4
4
8
width: 3the pointer is released.
width: 1the pointer is released.
*/