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Expertise: Advanced
Language: C++

July 17, 1998

Placement new

Operator new allocates memory from the heap, on which an object is constructed. Standard C++ also supports placement new operator, which constructs an object on a pre-allocated buffer. This is useful when building a memory pool, a garbage collector or simply when performance and exception safety are paramount (there's no danger of allocation failure since the memory has already been allocated, and constructing an object on a pre-allocated buffer takes less time):

 
void placement() {

char *buf  = new char[1000];   //pre-allocated buffer
	string *p = new (buf) string("hi");  //placement new
	string *q = new string("hi");  //ordinary heap allocation
	cout<c_str()<c_str();<