C++ Overload operator% for two doubles - c++

Question

is it possible to overload the operator% for two doubles?
const double operator%(const double& lhs, const double& rhs)
{
return fmod(lhs, rhs);
}
Of course, this generates an error because one of the two parameters must have a class type.
So I thought about utilizing the possibility of implicit constructor calls of C++ to get around of this problem. I did it in the following way:
class MyDouble {
public:
MyDouble(double val) : val_(val) {}
~MyDouble() {}
double val() const { return val_; }
private:
double val_;
};
const double operator%(const MyDouble& lhs, const double& rhs)
{
return fmod(lhs.val(), rhs);
}
const double operator%(const double& lhs, const MyDouble& rhs)
{
return fmod(lhs, rhs.val());
}
... and:
double a = 15.3;
double b = 6.7;
double res = a % b; // hopefully calling operator%(const MyDouble&, const double) using a implicit constructor call
Unfortunately, this does not work! Any hints, ideas, ... are appreciated!
Thanks in advance,
Jonas

Answer 1

The reason this doesn't work is because overload resolution for user defined operator functions is only triggered if at least one operand of the expression has a class or enumeration type.
So you are out of luck. This won't work.
I think the best you could try is waiting for a C++0x compiler and instead of writing 3.14, you write 3.14_myd, as a user defined literal.

Answer 2

alternatively, implement double MyDouble::operator%(const double&) const;, like so:
#include <iostream>
#include <cmath>
class t_double {
public:
t_double(const double& val) : d_val(val) {
}
t_double(const t_double& other) : d_val(other.d_val) {
}
~t_double() {
}
const double& val() const {
return this->d_val;
}
double operator%(const double& rhs) const {
return fmod(this->val(), rhs);
}
double operator%(const t_double& rhs) const {
return fmod(this->val(), rhs.val());
}
private:
double d_val;
};
int main(int argc, char* const argv[]) {
const t_double a(15.3);
const t_double b(6.7);
std::cout << a % b << " == " << a.val() << " % " << b.val() << "\n";
return 0;
}