Three patterns of new C + + dynamic memory opening

1.new operator and operator new

New New operator

Delete delete operator

operator new operator NEW

operator delete operator delete

void Main ()

{

date *p_date = (date *)operator new (sizeof (date)); //Just open up space

New (p_date) Date      (1, 1, 1); //Positioning new

P_date->~date (); //The display call of the destructor

operator Delete      (p_date); //release of Space

//equivalent to

date *p_date = new date(1,1,1);

Delete p_date;

//Note: This will cause a memory leak

void* p_date = new date (1, 1, 1);

operator Delete ( p_date       ); (equivalent to free)

//new opened the space and called the constructor, but at the time of the destruction, the system only analyzed the space pointed to by P_date, and did not call the destructor

//Because p_date is a pointer of type void, the system does not know that it is an object, so no destructor is called

}

2. positioning new//placement new

New (primitive pointer) type (initialization of the parameter list);

Note: Constructs an object of a class in the position indicated by the pointer p in the original space

Example: New ( P ) Date (ten);

void * operator new (size_t sz, Date* d , int pos) //Locating the new function (overloaded)

{

return &d [pos];

}

void * operator new (size_t sz,int*d,int POS)

{

return &d [pos];

}

void Main ()

{

date *p = new date;

New (p) Date (1995, 1, 31);

date *p = new date[10];

New (p,2) Date        (1995, 1, 31); //Position new application, initialize the second element

int a[10];

New (A, 5) int (10);

}

3. Three new instances:

#include <iostream>

#include <string>

using namespace std;

void * operator new (size_t n) //operator new

{

return malloc (n );

}

void operator delete (void *p) //operator Delete

{

Free ( p );

}

void * operator new[] (size_t n) //operator new[]

{

return malloc (n );

}

void operator delete[] (void *p) //operator delete[]

{

Free ( p );

}

class Date

{

Public:

Date ( int x = 0): _date (x)

{

}

~date ()

{}

protected :

int _date;

};

Simulation implementation of new, delete

void Test ()

{

date *p = (date *) operator new (sizeof (date)); //Open Space

for (int i = 0; i < 5; i++)

{

New (P + i) Date        (I*10); //placement New (positioning new) where to hit!!!

}

for (int i = 0; i < 5; i++)

{

(P + i)->~date (); //Show off destructor

}

operator Delete        (p); //Free space

}

void Main ()

{

Test ();

}

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Three patterns of new C + + dynamic memory opening