Question

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C++'s “placement new”

in the below code what does Line 3 represents, is it the way of typecasting? or what

 void someCode()
 {
   char memory[sizeof(Fred)];     // Line #1
   void* place = memory;          // Line #2

   Fred* f = new(place) Fred();   // Line #3
   // The pointers f and place will be equal

   ...
 }

Answer 1

This is a typical usage of Placement new.
It allows you to allocate memory and then construct objects at that particular memory location.

Line #3 essentially just calls the constructor Fred::Fred(). The this pointer in the Fred constructor will be equal to place. The returned pointer f will therefore be equal to place.