explicit

  • Article

C++ Specific

This keyword is a declaration specifier that can only be applied to in-class constructor declarations. Constructors declared explicit will not be considered for implicit conversions. For example:

class X {
public:
   explicit X(int);      //legal
   explicit X(double) {   //legal
      // ...
   }
};

explicit X::X(int) {}      //illegal

An explicit constructor cannot take part in implicit conversions. It can only be used to explicitly construct an object. For example, with the class declared above:

void f(X) {}
void g(int I) {
   f(i);      // will cause error
}
void h() {
   X x1(1);      // legal
}

The function call f(i) fails because there is no available implicit conversion from int to X.

Note   It is meaningless to apply explicit to constructors with multiple arguments, since such constructors cannot take part in implicit conversions.

END C++ Specific