Use of overloaded operator ambiguous - c++

Question

The following code:
typedef void HELPER;
const HELPER* helper = _helper;
inline ostream& operator <<(ostream& out, const HELPER* arg)
{ out << (const char*)(arg); return out; }
Blows up if I attempt a
cout << helper;
Specifically, I get:
main.cpp:35:28: error: use of overloaded operator '<<' is ambiguous
(with operand types 'basic_ostream >' and 'const HELPER *' (aka 'const void *'))
and it lists a few candidates:
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/ostream:207:0: note: candidate function
basic_ostream& operator<<(const void* __p);
^
main.cpp:25:17: note: candidate function
inline ostream& operator <<(ostream& out, const HELPER* arg)
^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/ostream:195:20: note: candidate function
basic_ostream& operator<<(bool __n);
^
I'm a little surprised that my typedef isn't invoking a stronger type matching here. How can I get this operator overload running?
EDIT: Further clarification, the purpose of this code is that I am dual-targeting a set of Arduino libraries. They manage their strings frequently with:
typedef void __FlashStringHelper;
void showHelp(const __FlashStringHelper* helpText)
{
Serial.print(helpText);
}
I like iostream and planned on this dual target, so I overloaded << on Serial object and made the previous into (this is the oversimplified version, for example)
#define cout Serial
void showHelp(const __FlashStringHelper* helpText)
{
cout << helpText;
}
Now I want to actually target real iostream for a different arch, but the old Arduino code can't vary (much) from its __FlashStringHelpers. That's where I'm at

Answer 1

typedef doesn't create types it aliases them,
inline ostream& operator <<(ostream& out, const HELPER* arg)
is equivalent to
inline ostream& operator <<(ostream& out, const void* arg)
Maybe you wanted to create a type named HELPER
class HELPER{};

Answer 2

As Zekian answered your question this here is something that may be of use to you or help you to achieve what you are trying to do.
#include <iostream>
template <class T>
class Helper {
private:
T obj_;
public:
explicit Helper<T>( T obj ) : obj_(obj) {}
public:
T getObj() const { return obj_; }
void setObj( T obj ) { obj_ = obj; }
template<class U>
inline friend std::ostream& operator<< ( std::ostream& out, const Helper<U>& rhs );
};
template<class U>
std::ostream& operator<< ( std::ostream& out, const Helper<U>& rhs ) {
return out << rhs.obj_;
}
int main() {
Helper<int> helper( 3 );
std::cout << helper << std::endl;
return 0;
}
It is a wrapper class template with an overloaded ostream operator<<. This will work for integral and atomic types. If you pass another struct or class object then you will have to define other overloaded ostream operators for them.
Example - Same Class Template, but this time using a class or struct.
#include <iostream>
template <class T>
class Helper {
private:
T obj_;
public:
explicit Helper<T>( T obj ) : obj_(obj) {}
public:
T getObj() const { return obj_; }
void setObj( T obj ) { obj_ = obj; }
template<class U>
inline friend std::ostream& operator<< ( std::ostream& out, const Helper<U>& rhs );
};
template<class U>
std::ostream& operator<< ( std::ostream& out, const Helper<U>& rhs ) {
return out << rhs.obj_;
}
struct Staff {
int employees = 4; // Default to 4
};
int main() {
Staff staff;
Helper<Staff> helper( staff );
std::cout << helper << std::endl; // will not compile
return 0;
}
To fix this ostream will need an overloaded operator for Staff object
template <class T>
class Helper {
private:
T obj_;
public:
explicit Helper<T>( T obj ) : obj_(obj) {}
public:
T getObj() const { return obj_; }
void setObj( T obj ) { obj_ = obj; }
template<class U>
inline friend std::ostream& operator<< ( std::ostream& out, const Helper<U>& rhs );
};
template<class U>
std::ostream& operator<< ( std::ostream& out, const Helper<U>& rhs ) {
return out << rhs.obj_;
}
struct Staff {
int employees = 4;
inline friend std::ostream& operator<< ( std::ostream& out, const Staff& rhs );
};
std::ostream& operator<<( std::ostream& out, const Staff& rhs ) {
return out << rhs.employees;
}
int main() {
Staff staff;
Helper<Staff> helper( staff ); // Default to 4
std::cout << helper << std::endl; // Will Print 4
// To Change Staff's Employee count for the helper wrapper do this:
staff.employees = 12; // Change To 12
helper.setObj( staff ); // pass the changed struct back into helper
std::cout << helper3 << std::endl; // Will Now Print 12
// And For Other Default Types
Helper<int> helper2( 3 );
std::cout << helper2 << std::endl;
Helper<float> helper3( 2.4f );
std::cout << helper3 << std::endl;
return 0;
}