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  1. // file: date.h
  2. #include <cstdio>
  3.  
  4. class date
  5. {
  6.   friend bool operator<(date d1, date d2);
  7. public:
  8.   // constructor    
  9.   date(int y=2015, int m=1, int d=1) : year(y), month(m), day(d) { }
  10.   // explicit constructor
  11.   explicit date(const char *s);
  12. private:
  13.   int year;
  14.   int month;
  15.   int day;
  16. };
  17.  
  18. // question: use member or global operators?
  19. bool operator<(date d1, date d2);
  20. inline bool operator==(date d1, date d2) { return !(d1<d2 || d2<d1); }
  21. inline bool operator!=(date d1, date d2) { return d1<d2 || d2<d1; }
  22. inline bool operator<=(date d1, date d2) { return !(d2<d1); }
  23. inline bool operator>=(date d1, date d2) { return !(d1<d2); }
  24. inline bool operator>(date d1, date d2)  { return d2<d1; }
  25.  
  26.  
  27. // file: date.cpp
  28. date:: date(const char *s)
  29. {
  30.   sscanf(s, "%d.%d.%d", &year, &month, &day);
  31. }
  32.  
  33. bool operator<(date d1, date d2)
  34. {
  35.   return d1.year < d2.year || d1.month < d2.month || d1.day < d2.day;
  36. }
  37.  
  38.  
  39. // file: main.cpp
  40. int main()
  41. {
  42.   date d(2015, 3, 12);
  43.  
  44.   if (d < date(2000, 1, 1))         // works: explicit call of constructor 
  45.   {
  46.     /* ... */
  47.   }
  48.   else if (d < 2000)                // works: implicit constructor
  49.   {
  50.     /* ... */
  51.   }
  52.   else if (d < "2015.1.12")         // does not work: explicit constructor
  53.   {
  54.     /* ... */
  55.   }
  56.   else if (d < date("2015.1.12"))   // works: explicit call of constructor 
  57.   {
  58.     /* ... */
  59.   }
  60. }
Compilation error #stdin compilation error #stdout 0s 0KB
comments (?)
stdin
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Standard input is empty
compilation info 
prog.cpp: In function 'int main()':
prog.cpp:52:16: error: invalid conversion from 'const char*' to 'int' [-fpermissive]
   else if (d < "2015.1.12")         // does not work: explicit constructor
                ^
prog.cpp:9:3: note: initializing argument 1 of 'date::date(int, int, int)'
   date(int y=2015, int m=1, int d=1) : year(y), month(m), day(d) { }
   ^
stdout
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Standard output is empty
https://ideone.com/6uREOg
Advanced CPP: Constructors, destructors
Explicit constructor
language:
C++ (gcc 8.3)
created:
9 years ago
visibility:
secret

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