Placement New Syntax

How can a C++ developer use the placement new syntax to make new allocate an object of class SomeClass at a particular memory address stored in a pointer type variable named pmem?

A. new SomeClass(pmem);
B. new(pmem) SomeClass;
C. new SomeClass pmem;
D. new pmem SomeClass;
E. new (pmem, SomeClass);

dlee6565
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Jul 23rd, 2009
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bfeingold
Profile Answers by bfeingold

Jul 29th, 2009

B. looks closest to correct. I would use:

SomeClass* ptr = new(pmem)SomeClass();

krislogy
Profile Answers by krislogy

Oct 13th, 2009

It is B , provided pmem is an allocated pointer (meaning memory already allocated to it).

See this link for more explanation: http://www.geekinterview.com/question_details/16559

tawofala
Profile Answers by tawofala

Nov 14th, 2009

E. new (pmem, SomeClass);

sachin_mundhra
Profile Answers by sachin_mundhra

Dec 18th, 2009

B) new(pmem) SomeClass;

akash_saxena
Profile Answers by akash_saxena

Dec 22nd, 2009

It is
B. new(pmem) SomeClass;

pmem points to the memory which shall be used.

ajrobb
Profile Answers by ajrobb

Sep 22nd, 2010

B

Where you use placement new, it is important to explicitly call the destructor for the object before re-using the memory.

Fred * fred = new(pmem) Fred();
...
fred->~Fred();
fred = 0;

George * george(pmem) George();