Question

I am making a fraction class for a school project, and my brain is frying. I was told to overload the << and >> operators through the friend keyword. But I’m getting errors for this.

I’ve posted the relevant code here: http://pastebin.com/NgCABGJ2

The errors include: error C2270: ‘<<‘ : modifiers not allowed on nonmember functions (this error is for all the ones that are declared as friends)

This was at the operator< definition. error C2333: ‘Fraction::operator <‘ : error in function declaration; skipping function body

There’s 46 in all… this is a nightmare.

EDIT:

Thanks, I solved almost all the errors, but there’s still 3

error C2664: ‘Fraction::Fraction(const Fraction &)’ : cannot convert parameter 1 from ‘int’ to ‘const Fraction &’
Occurs at this statement:

Fraction<int> test1, test2, test3(10);

error C2248: ‘Fraction::operator ==’ : cannot access private member declared in class ‘Fraction’
error C2248: ‘Fraction::operator <‘ : cannot access private member declared in class ‘Fraction’

I don’t understand these two, but it occurs at these statements:

    if (test1 == test2)
    cout << "\nTest1 is equal to Test2";
if (test1 < test2)
    cout << "\nTest1 is less than Test2";

Thanks!

<><><>>EDIT2<<><><>

I fixed the other private access errors, but now i have some reaaaaaaaally bizarre errors:

Full code: http://pastebin.com/MVrB67SR

Errors:

Error 1 error LNK2001: unresolved external symbol “class Fraction __cdecl operator-(class Fraction const &,class Fraction const &)” (??G@YA?AV?$Fraction@H@@ABV0@0@Z)
Error 2 error LNK2001: unresolved external symbol “class Fraction __cdecl operator+(class Fraction const &,class Fraction const &)” (??H@YA?AV?$Fraction@H@@ABV0@0@Z)
Error 3 error LNK2001: unresolved external symbol “class Fraction __cdecl operator/(class Fraction const &,class Fraction const &)” (??K@YA?AV?$Fraction@H@@ABV0@0@Z) c:\Users\caleb jares\documents\visual studio 2010\Projects\Solution11-5\Solution11-5\Solution11-5.obj
Error 4 error LNK2001: unresolved external symbol “class Fraction __cdecl operator*(class Fraction const &,class Fraction const &)” (??D@YA?AV?$Fraction@H@@ABV0@0@Z)
Error 5 error LNK2001: unresolved external symbol “class std::basic_ostream > & __cdecl operator<<(class std::basic_ostream > const &,class Fraction)” (??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@ABV01@V?$Fraction@H@@@Z)
Error 6 error LNK2001: unresolved external symbol “class std::basic_istream > & __cdecl operator>>(class std::basic_istream > const &,class Fraction)” (??5@YAAAV?$basic_istream@DU?$char_traits@D@std@@@std@@ABV01@V?$Fraction@H@@@Z)
Error 7 error LNK1120: 6 unresolved externals

Again, thanks for help!

Answer 1

Sounds like you tried to declare friend ostream &operator<<(…) const; . The important thing about friends is that they are not members. A friend function exists outside the scope of the class, even if it is defined inside the class {} block. In other words, you are declaring a function ::operator<<(), not fraction::operator<<(). And only member functions can have that trailing const, since it modifies the type of this.

Fact is, operator<< for output usually shouldn’t be a friend anyway. It just gets the value and forwards it to the stream… that shouldn’t require any special permission! Same applies to operator<.

Take the functions outside the class block entirely. There’s no way your TA can complain about your design using friend less often.