1. #include <iostream>
  3. class A
  4. {
  5. public:
  6. A(const char* cname) : name(cname)
  7. {
  8. std::cout << "constructing " << cname << std::endl;
  9. }
  10. ~A(){
  11. std::cout << "destructing " << name.c_str() << std::endl;
  12. }
  13. A(A const& a)
  14. {
  15. if (name.empty()) name = "*tmp copy*";
  16. std::cout << "creating " << name.c_str() << " by copying " << a.name.c_str() << std::endl;
  17. }
  18. A& operator=(A const& a)
  19. {
  20. std::cout << "assignment ( " << name.c_str() << " = " << a.name.c_str() << " )"<< std::endl;
  21. return *this;
  22. }
  24. std::string name;
  25. };
  27. A foo()
  28. {
  29. A b("b");
  30. return b;
  31. }
  33. int main()
  34. {
  35. A a("a");
  36. a = foo();
  37. }

output without NRVO:

constructing a

constructing b

creating *tmp copy* by copying b

destructing b

assignment ( a = *tmp copy* )

destructing *tmp copy*

destructing a

output with NRVO:

constructing a

constructing b

assignment ( a = b )

destructing b

destructing a