delete釋放的指針，再訪問
例1
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#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
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#include <iostream>using namespace std;int * func(){ int * a = new int(10); return a;}int main(){ int * p = func(); cout << *p << endl;//10 //delete關鍵字用來釋放堆區數據 delete p;// p = new int(5); cout << *p << endl;//10 return 0;} |
//輸出
// 10
// 16584968
解釋：
訪問 delete 之后的內存是一個未定義行為。 未定義行為可能產生任何結果，包括但不限于：產生期望的結果，產生未期望的結果，產生隨機的結果，產生無法解釋的結果，運行錯誤，隨機的運行時錯誤，編譯錯誤，等等 ---- 你只是放棄了對這片內存的所有權。獲得所有權的人對這片內存做什么（或者說什么都不做）都不關你的事
static 變量的儲存區域
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
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#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創建的對象，必須自己用delete回收，不然系統不會幫助回收，出現內存泄漏 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 靜態變量和普通變量地址不連續，是靜態變量存在數據段0xe91470 普通變量存在 開辟的堆上0xe914744 指針大小8 對象所占內存大小8 類大小point 0x61fefc 新對象a的地址0x405004 靜態變量地址不變，靜態變量屬于整個類0x61fefc 屬于局部變量，普通變量存在 棧空間上0x61ff00488point 0x61fef4 新對象b的地址， b與a之間相差8個字節0x405004 靜態變量地址不變，靜態變量屬于整個類0x61fef4 屬于局部變量，普通變量存在 棧空間上，地址連續0x61fef848width: 3the pointer is released. 自動調用析構函數width: 1the pointer is released. 自動調用析構函數*/ |
例2 幫助理解
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#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 0x7914700x405004 0x791470 0x791474 488point 0x7911080x405004 0x791108 0x79110c 488width: 10the pointer is released.width: 30the pointer is released.point 0x61fef80x4050040x61fef80x61fefc488point 0x61fef00x4050040x61fef00x61fef448width: 3the pointer is released.width: 1the pointer is released.*/ |
總結
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原文鏈接：https://blog.csdn.net/qq_44888950/article/details/120442843
