Page585_multiple_conversion.cpp

// Warning: this is for verification. It cannot compile.
struct A {
    A(int = 0); // usually a bad idea to have two
    A(double);  //conversions from arithmetic types
    operator int() const;       // usually a bad idea to have two
    operator double() const;    // conversions to arithmetic types
    // other members
};
int main()
{
    // ambiguity #1
    void f2(long double);
    A a;
    f2(a); // error ambiguous: f(A::operator int())
           //              or: f(A::operator double())
    // ambiguity #2
   long lg = 0;
    A a2(lg); // error ambiguous: A::A(int) or A::A(double)
    // #3
    // promoting short to int is better than converting short to double
    short s = 42;
    A a3(s); // use A::A(int)
    return 0;
}
void f2(long double) {}
// Note: #1 is ambiguous because conversion from int to long double and double
// from long double has the same rank(there's no "float promotion");
// #2 is ambiguous because conversion from long to int and double to int has the
// same rank(shrink from long to int is arithmetic conversion rather than
// integral promotion).