CODEWITHSUNDEEP
c++constructor
youssef
youssef

Reputation: 623

How to solve ambiguity between conversion constructor and normal constructor?

I was looking forward to remove ambiguity between normal constructor and auto-conversion constructor.

as far as I know this ambiguity can be partially removed by declaring normal constructor as explicit so compilers will avoid using this constructor as conversion constructor like following:

#include <iostream>
#include <fstream>

class Integer{
  int i ;

public:

  explicit  Integer (const int _i) : i(_i) {} //Normal constructor
  Integer (const int& ii ) : i (ii) {}        // conversion constructor
  operator int() {return int (i) ;}         // Auto-conversion operator

  friend std::ostream & operator <<(std::ostream &os, const Integer io ) {
    std::cout << io.i  ;
    return os ;
}

};


int main() {

// Integer io (5); call of overloaded ‘Integer(int)’ is ambiguous error 
  Integer io2 = 20 ;          // conversion constructor
  std:: cout << io2 << "\n" ;
  int i = io2 ;               // auto-conversion operator
  std:: cout << i << "\n" ;
}

output :

20
20

my questions are:

1- Is there a standard way to force using a constructor as conversion constructor, since there is a standard way to force usage as normal constructor?

2- is it a good practice to use conversion constructor and autoconversion operators, in another words can I ensure that different compilers will use the constructor as conversion constructor in case if normal contructor is not overloaded with conversion constructor ?

My thanks

Upvotes: 4

Views: 667

Answers (1)

Charles
Charles

Reputation: 1153

Is there a standard way to force using a constructor as conversion constructor, since there is a standard way to force usage as normal constructor?

Yes, you omit the explicit keyword.

is it a good practice to use conversion constructor and autoconversion operators, in another words can I ensure that different compilers will use the constructor as conversion constructor in case if normal contructor is not overloaded with conversion constructor ?

If the compiler is standards compliant, then there are no issues here. There's nothing wrong with implicit constructions. They can be quite handy when you're constructing literal arrays of objects and such. Can also be surprising. Use your judgement.

Upvotes: 1

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