C++ new/delete 重載__C++

 首先，new和delete是運算子，重載new和delete是可能的。這樣做的原因是，有時希望使用某種特殊的動態記憶體分配方法。例如，可能有些分配子程式，他們的堆已耗盡，自動開始把一個磁碟檔案當虛儲存使用，或者使用者希望控制某一片儲存空間的分配等。

重載new和delete的格式如下：

void *operator new (size_t size){  .......//完成分配工作  return pointer_to_memory;}void operator delete(void *p){  ......//釋放由p指向的儲存空間}

1.局部重載new和delete（可以使用成員函數和友元函數兩種方式重載）
      使用new分配某個重載了new的累的對象空間時，先調用new的重載函數，再調用該類的建構函式，如果該類的建構函式有參數要求，則必須給出對應的實參。
      使用了delete釋放某個重載了delete的累的對象空間時，先調用類的解構函式，然後再調用重載的delete函數。

#include <iostream>#include <stdlib.h>#include <string.h>using namespace std;class three_d{private:    int x,y,z;public:    three_d(int a,int b,int c);    ~three_d()    {        cout << "Destructing\n";    }    void *operator new(size_t size);    void operator delete(void *p);    friend ostream & operator <<(ostream &stream,three_d obj);};three_d::three_d(int a,int b,int c){    cout << "Constructing\n";    x = a;    y = b;    z = c;}void *three_d::operator new(size_t size){    cout << "in threee_d new\n";    return malloc(size);}void three_d::operator delete(void *p){    cout << "in three_d delete\n" ;    free(p);}ostream &operator <<(ostream &os,three_d obj){    os << obj.x << ",";    os << obj.y << ",";    os << obj.z << "\n";    return os;}int main(int argc,char *argv[]){    three_d *p = new three_d(1,2,3);    three_d *p1 = new three_d(4,5,6);    if(!p || !p1)    {        cout << "Allocation failure" << endl;        return 1;    }    cout << *p << *p1;    delete p;    delete p1;    int *pnum;    pnum = new int;    *pnum = 0;    cout << "num = " << *pnum << endl;    delete pnum;    cout << "Application Run Successfully!" << endl;    return 0;}

2.全域重載new和delete
      可以在任何類說明之外重在new和delete，使它們成為全域的。當new和delete被重載為全域時，C++原來的new與delete被忽略，並且重載的運算子用於所有類型（包括標準型和使用者定義型別）的分配要求。

#include <iostream>#include <stdlib.h>#include <string.h>using namespace std;class three_d{private:    int x,y,z;public:    three_d(int a,int b,int c);    ~three_d()    {        cout << "Destructing\n";    }    friend ostream & operator <<(ostream &stream,three_d obj);};three_d::three_d(int a,int b,int c){    cout << "Constructing\n";    x = a;    y = b;    z = c;}void *operator new(size_t size){    cout << "in threee_d new\n";    return malloc(size);}void operator delete(void *p){    cout << "in three_d delete\n" ;    free(p);}ostream &operator <<(ostream &os,three_d obj){    os << obj.x << ",";    os << obj.y << ",";    os << obj.z << "\n";    return os;}int main(int argc,char *argv[]){    three_d *p = new three_d(1,2,3);    three_d *p1 = new three_d(4,5,6);    if(!p || !p1)    {        cout << "Allocation failure" << endl;        return 1;    }    cout << *p << *p1;    delete p;    delete p1;    int *pnum;    pnum = new int;    *pnum = 0;    cout << "num = " << *pnum << endl;    delete pnum;    cout << "Application Run Successfully!" << endl;    return 0;}