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  1. #include <iostream>
  2.  
  3. // stub logging object to make the example work - just logs to stdout
  4. struct Log
  5. {
  6.     template<typename T>
  7.     friend Log& operator<<(Log& l, T d)
  8.     {
  9.         std::cout << d;
  10.         return l;
  11.     }
  12.     friend Log& operator<<(Log& l, std::ostream& (*f)(std::ostream&))
  13.     {
  14.         std::cout << f;
  15.         return l;
  16.     }
  17. };
  18. Log gLog;
  19.  
  20. #define LOG Base::GetLog()
  21.  
  22. // GetLog in the global namespace for non-Context derived classes, free functions etc
  23. struct Base {
  24.     static Log& GetLog()
  25.     {
  26.         return gLog;
  27.     }
  28. };
  29.  
  30. // classes derive from this to add context specific information when logging
  31. template <typename Self>
  32. struct Context
  33. {
  34.     // this GetLog adds prefix to Context derived classes
  35.     Log& GetLog()
  36.     {
  37.         static_cast<const Self*>(this)->Token(gLog); // add the Context's Token to the log
  38.         return gLog << ": ";
  39.     }
  40. };
  41.  
  42. //-------------------------
  43.  
  44. template<typename T>
  45. struct Foo : Context<Foo<T>>
  46. {
  47.     typedef Context<Foo<T>> Base;
  48.  
  49.     void Func1()
  50.     {
  51.         LOG << __func__ << std::endl;
  52.     }
  53.     void Func2()
  54.     {
  55.         LOG << __func__ << std::endl;
  56.     }
  57.  
  58.     Log& Token(Log& l) const { return l << "Foo"; }
  59. };
  60.  
  61. // logging inside a non-Context derived class
  62. struct Bar
  63. {
  64.     void Func()
  65.     {
  66.         LOG << __func__ << std::endl;
  67.     }
  68. };
  69.  
  70. // logging inside a free function 
  71. void Baz()
  72. {
  73.     LOG << __func__ << std::endl;
  74. }
  75.  
  76. //-------------------------
  77.  
  78. int main()
  79. {
  80.     Foo<int> f;
  81.     f.Func1();
  82.     f.Func2();
  83.  
  84.     Bar b;
  85.     b.Func();
  86.  
  87.     Baz();
  88.  
  89.     return 0;
  90. }
Success #stdin #stdout 0s 2896KB
comments (?)
stdin 
Standard input is empty
stdout 
Foo: Func1
Foo: Func2
Func
Baz
https://ideone.com/KzVNZu
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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