operator new (<new>)

Articolo
07/29/2015

The allocation function called by a new expression to allocate storage for an array of objects.

void *operator new[]( 
   std::size_t _Count 
) 
   throw(std::bad_alloc); 
void *operator new[]( 
   std::size_t _Count, 
   const std::nothrow_t& 
) throw( ); 
void *operator new[]( 
   std::size_t _Count,  
   void* _Ptr 
) throw( );

Parameters

_Count
The number of bytes of storage to be allocated for the array object.
_Ptr
The pointer to be returned.

Return Value

A pointer to the lowest byte address of the newly-allocated storage. Or _Ptr.

Remarks

The first function is called by a new[] expression to allocate _Count bytes of storage suitably aligned to represent any array object of that size or smaller. The program can define a function with this function signature that replaces the default version defined by the Standard C++ Library. The required behavior is the same as for operator new(size_t). The default behavior is to return operator new(_Count).

The second function is called by a placement new[] expression to allocate _Count bytes of storage suitably aligned to represent any array object of that size. The program can define a function with this function signature that replaces the default version defined by the Standard C++ Library. The default behavior is to return operator new(_Count) if that function succeeds. Otherwise, it returns a null pointer.

The third function is called by a placement new[] expression, of the form new (args) T[N]. Here, args consists of a single object pointer. The function returns _Ptr.

To free storage allocated by operator new[], call operator delete[].

For information on throwing or nonthrowing behavior of new, see The new and delete Operators.

Example

// new_op_alloc.cpp
// compile with: /EHsc
#include <new>
#include <iostream>

using namespace std;

class MyClass {
public:
   MyClass() {
      cout << "Construction MyClass." << this << endl;
   };

   ~MyClass() {
      imember = 0; cout << "Destructing MyClass." << this << endl;
      };
   int imember;
};

int main() {
   // The first form of new delete
   MyClass* fPtr = new MyClass[2];
   delete[ ] fPtr;

   // The second form of new delete
   char x[2 * sizeof( MyClass ) + sizeof(int)];
   
   MyClass* fPtr2 = new( &x[0] ) MyClass[2];
   fPtr2[1].~MyClass();
   fPtr2[0].~MyClass();
   cout << "The address of x[0] is : " << ( void* )&x[0] << endl;

   // The third form of new delete
   MyClass* fPtr3 = new( nothrow ) MyClass[2];
   delete[ ] fPtr3;
}

Sample Output

Construction MyClass.00311AEC
Construction MyClass.00311AF0
Destructing MyClass.00311AF0
Destructing MyClass.00311AEC
Construction MyClass.0012FED4
Construction MyClass.0012FED8
Destructing MyClass.0012FED8
Destructing MyClass.0012FED4
The address of x[0] is : 0012FED0
Construction MyClass.00311AEC
Construction MyClass.00311AF0
Destructing MyClass.00311AF0
Destructing MyClass.00311AEC

Requirements

Header: <new>

Namespace: std

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