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  1. #include <iostream>
  2. #include <string>
  3.  
  4. struct A
  5. {
  6.     A() { std::cout << "A:: default constructor\n" ; }
  7.  
  8.     A( const char* aa ) : a(aa) { std::cout << "A:: one arg constructor\n" ; }
  9.  
  10.     A ( const A& that ) : a(that.a) { std::cout << "A:: copy constructor\n" ; }
  11.  
  12.     A& operator= ( const A& that )
  13.     {
  14.         std::cout << "A:: assignment\n" ;
  15.         a = that. a ;
  16.         return *this ;
  17.     }
  18.  
  19.     std::string a ;
  20. };
  21.  
  22. #include <map>
  23.  
  24. int main()
  25. {
  26.     std::map< int, A > map ;
  27.  
  28.     {
  29.         // possibly only if A is DefaultConstructible
  30.         map[1] = "hello world" ;
  31.         /*
  32.         A:: one arg constructor
  33.         A:: default constructor
  34.         A:: assignment
  35.         */
  36.     }
  37.     std::cout << "------------------------\n" ;
  38.     {
  39.         // possibly only if A is CopyConstructible
  40.         map.insert( { 2, "hello again" } ) ;
  41.         /*
  42.         A:: one arg constructor
  43.         A:: copy constructor
  44.         */
  45.     }
  46.     std::cout << "------------------------\n" ;
  47.     {
  48.         map.emplace( 3, "hello for a third time" ) ;
  49.         // A:: one arg constructor
  50.     }
  51. }
  52.  
Success #stdin #stdout 0s 3476KB
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stdin
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Standard input is empty
stdout
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A:: one arg constructor
A:: default constructor
A:: assignment
------------------------
A:: one arg constructor
A:: copy constructor
------------------------
A:: one arg constructor
https://ideone.com/iqxyzf
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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