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  1. #include <iostream>
  2. #include <string>
  3.  
  4. std::string m_str;
  5.  
  6. void a(std::string&& other) 
  7. {
  8. 	m_str = std::string(other); // this is wrong
  9. 	std::cout << "a: " << other << std::endl;
  10. 	// other is not EMPTY because inside the function,
  11. 	// the argument "other" got a name, and lost it's "rvalueness"
  12. }
  13.  
  14. void b(std::string&& other)
  15. {
  16. 	m_str = std::string(std::move(other));
  17. 	std::cout << "b: " << other << std::endl;
  18. 	// other is empty because std::move converted the lvalue "other" back to "rvalue"
  19. }
  20.  
  21. void c(std::string&& other)
  22. {
  23. 	m_str = std::string(std::forward<std::string>(other)); // other is empty as well.
  24. 	// because this function only accepts RValues, so std::forward does the same as std::move
  25. 	// if you call this function with a lvalue, you will get compile error.
  26. 	std::cout << "c: " << other << std::endl;
  27. }
  28.  
  29. //This functions accepts both rvalues and lvalues (other is a "forwarding reference")
  30. template<typename T>
  31. void d(T&& other) 
  32. {
  33. 	m_str = std::string(std::forward<T>(other)); //If you use move here, other will always be empty.
  34. 	std::cout << "d: " << other << std::endl;
  35. 	// If other was an rvalue, other will be empty.
  36. 	// If other was an lvalue, other will NOT be empty.
  37. }
  38.  
  39. int main() 
  40. {
  41. 	a(std::string("Hello World"));
  42. 	b(std::string("Hello World"));
  43. 	c(std::string("Hello World"));
  44. 	d(std::string("Hello World"));
  45. 	std::string lvalue = "Hello World";
  46. 	d(lvalue);
  47. 	return 0;
  48. }
Success #stdin #stdout 0s 3460KB
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stdin
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Standard input is empty
stdout
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a: Hello World
b: 
c: 
d: 
d: Hello World
https://ideone.com/zmYFq8
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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