Re: new and delete

Below is a small code about memory allocation and deallocation.

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

class X {
public:
 void* operator new(size_t sz) throw (const char*) {
   void* p = malloc(sz); //LINE1
   if (p == 0) throw "malloc() failed";
   return p;
 }

 void operator delete(void* p) {
   free(p);
 }

};

class Y {
 int filler[100];
public:

 // two arguments
 void operator delete(void* p, size_t sz) throw (const char*) {
   cout << "Freeing " << sz << " byte(s)" << endl; //LINE2
   free(p);
 };

};

int main() {
 X* ptr = new X; //LINE3

 // call X::operator delete(void*)
 delete ptr;

 Y* yptr = new Y;

 // call Y::operator delete(void*, size_t)
 // with size of Y as second argument
 delete yptr; //LINE4
}

My questions are:
When LINE3 is executed, LINE1 is executed. How is the variable sz
assigned sizeof(X)?

The output of the code is:
Freeing 400 byte(s)
When LINE4 is executed, LINE2 is executed. How does sz get the value
400?