placement new c 2b 2b

1//placement new in c++
2char *buf  = new char[sizeof(string)]; // pre-allocated buffer
3string *p = new (buf) string("hi");    // placement new
4string *q = new string("hi");          // ordinary heap allocation
5/*Standard C++ also supports placement new operator, which constructs 
6an object on a pre-allocated buffer. This is useful when building a 
7memory pool, a garbage collector or simply when performance and exception 
8safety are paramount (there's no danger of allocation failure since the memory
9has already been allocated, and constructing an object on a pre-allocated
10buffer takes less time):
11*/