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In this noncompliant code example, the local variable s1space is passed as the expression to the placement new operator. The resulting pointer of that call is then passed to ::operator delete(), resulting in undefined behavior due to ::operator delete() attempting to free memory that was not returned by ::operator new().

#include <iostream>
 
struct S {
  S() { std::cout << "S::S()" << std::endl; }
  ~S() { std::cout << "S::~S()" << std::endl; }
};
 
void f() {
  char S s1space[sizeof(struct S)];
  S *s2s1 = new (&s1space) S;
 
  // ...
 
  delete s2s1;
}

Compliant Solution (placement new())

This compliant solution removes the call to ::operator delete(), allowing s1 to be destroyed as a result of its normal object lifetime terminationinstead explicitly calling s1's destructor. This is one of the few times when explicitly invoking a destructor is warranted.

#include <iostream>
 
struct S {
  S() { std::cout << "S::S()" << std::endl; }
  ~S() { std::cout << "S::~S()" << std::endl; }
};
 
void f() {
  char space[sizeof(struct S s1)];
  S *s2s1 = new (&s1space) S;
 
  // ...

  s1->~S();
}

Noncompliant Code Example (Uninitialized delete)

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