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  1. #include <stdio.h>
  2.  
  3. class Double
  4. {
  5. public:
  6.   Double operator +( Double other ){ printf( "Double::operator+(Double)\n" ); return *this; }
  7. };
  8. class Float
  9. {
  10. public:
  11.   operator Double(){ printf( "Float to Double\n" ); return Double(); }
  12. };
  13. class Float2
  14. {
  15. public:
  16.   operator Double(){ printf( "Float2 to Double\n" ); return Double(); }
  17.   Double operator +( Double other ){ printf( "Float2::operator+(Double)\n" ); return Double(); }
  18. };
  19.  
  20.  
  21. int main( void )
  22. {
  23.     Double  d;
  24.     Float   f;
  25.     Float2  f2;
  26.  
  27.     printf( "[1]\n" ); 
  28.     d + d;
  29.  
  30.     printf( "[2]\n" );
  31.     d + f; // fはDoubleへ暗黙の型変換が発生する。
  32.  
  33.     /* error: 左オペランドに暗黙の型変換は発生しないのでエラーになる。
  34.     f + d;
  35.     */
  36.  
  37.     printf( "[3]\n" );
  38.     f2 + d; // 左オペランドに暗黙の型変換は発生しないが、Float2はoperator+(Double)を持っているのでエラーにならない。
  39.  
  40.     return 0;
  41. }
Success #stdin #stdout 0s 3340KB
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stdin
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Standard input is empty
stdout
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[1]
Double::operator+(Double)
[2]
Float to Double
Double::operator+(Double)
[3]
Float2::operator+(Double)
https://ideone.com/WCiMNA
language:
C++ (gcc 8.3)
created:
10 years ago
visibility:
secret

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