Check out example codes for "placement new c++". It will help you in understanding the concepts better.
Code Example 1
//placement new in c++ char *buf = new char[sizeof(string)]; // pre-allocated buffer string *p = new (buf) string("hi"); // placement new string *q = new string("hi"); // ordinary heap allocation /*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): */
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