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  1. #include <iostream>
  2. #include <mutex>
  3.  
  4. class Foo
  5. {
  6. public:
  7.     Foo() : _i(NULL) {}
  8.     int get()
  9.     {
  10.         std::call_once(_flag,
  11.                        [&]()
  12.                        {
  13.                            std::cout << "Setting _i\n";
  14.                            _i = new int(5);
  15.                        });
  16.         return *_i;
  17.     }
  18.     Foo(const Foo&) = delete;
  19.     Foo& operator=(const Foo&) = delete;
  20. private:
  21.     std::once_flag _flag;
  22.     int* _i;
  23. };
  24.  
  25. int main()
  26. {
  27.     Foo f;
  28.  
  29.     std::cout << f.get() << "\n";
  30.     std::cout << f.get() << "\n";
  31.     std::cout << f.get() << "\n";
  32.     std::cout << f.get() << "\n";
  33.     std::cout << f.get() << "\n";
  34.     std::cout << f.get() << "\n";
  35.     std::cout << f.get() << "\n";
  36.     std::cout << f.get() << "\n";
  37.     return 0;
  38. }
  39.  
Success #stdin #stdout 0s 3060KB
comments (?)
stdin
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Standard input is empty
stdout
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Setting _i
5
5
5
5
5
5
5
5
https://ideone.com/lwwALg
language:
C++14 (gcc 8.3)
created:
13 years ago
visibility:
public

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