placement new

/*
We generally refer to placement new as overloading new() delete()
We can overload class member operator new(), provided that each version of the declaration has a unique parameter list,
The first parameter is size_t, and the rest of the parameters are initialized with the placement arguments specified by new.
foo* p = new(300,'c')foo;
*/

#include <iostream>
#include <cstdlib>
using namespace std;

class Bad{
	public:
		Bad(){
				cout<<"Allocated memory successfully!"<<endl;
		}
} ;

class foo{
	public:
		foo(){cout<<"foo::foo()"<<endl;
		}
		foo(int ){cout<<"foo::foo(int)"<<endl;throw Bad();//Throw expcetion here, test placement operator delete If it can throw an error, it means that the memory has been called .
		}
		//(1) Overload of general operator new()
		void* operator new(size_t size){
			return malloc(size);
		}
		//(2) This is the overloaded form of placement new() already provided by the standard library
		void * operator new(size_t size,void*start){
			return start;
		}
		//(3) This is a new placement new
		void * operator new(size_t size,long extra){
			return malloc(size+extra);
		}
		//(4) This is another placement new
		void * operator new(size_t size,long extra,char init){
			return malloc(size+extra);
		}
		//(5) This is another placement new but deliberately mistyped the type of the first parameter (must be size_t to conform to normal operator new)
		/*
		void* operator new(long extra,char init){
			return malloc(extra);
		}
		*/
		//We wrote 5 placement new above, then we should write 5 placement delete, but even if operator delete() cannot correspond to operator new one by one, there will be no error, which means giving up processing any abnormal.
};

int main(){
	foo str;
	foo* p1 = new foo;
	foo* p2 = new(&str)foo;
	foo* p3 = new(100)foo;
	foo* p4 = new (100,'a')foo;
	foo* p5 = new(100)foo(1);
	return 0;
}