🔒 Locked

Overloading operator is ambiguous?

Started by silverphyre673 Mar 13, 2005 at 11:06 PM 3 replies 3.3k views

Original Post

Mar 13, 2005 at 11:06 PM

I have a console class with pointers to cin and cout. I have this function:


template<class T>
Console & operator << ( Console & console, T & writeObj)
{
    console.outstream << writeObj;
    return console;
}

int main()
{
    string str = " hello ";
    Console console;
    console << "\n" << str << "\n";
}

Which gives me the errors: ambiguous overload for 'operator<<' in 'console << "\n"' std::ostream& operator<<(Console&, T&) [with T = const char[2]] How should I fix this? Thanks

Erzengeldeslichtes

Mar 14, 2005 at 1:50 AM

I believe the problem is that it doesn't like referances to static arrays.

Fruny

Mar 14, 2005 at 1:55 AM

Why is the return type in the error message an std::ostream&? I'm sure there is code you haven't shown us...

Like, does Console derive from std::ostream?

silverphyre673

Mar 14, 2005 at 4:02 AM

Well, I've changed a few things around...

Now, the write function (which works) looks like this:

template<class T>void Consol::Write( T & writeObj){    cout << T;}

What should I do to make it so that

a) You could pass an std::string to Write() and have it work

b) I could get this to work in the same manner as cout works:

Console console;string str1 = "my name is Ben."console << "Hello, World! " << str1 << "\n";

Thanks! Tell me if you need more info

Erzengeldeslichtes

Mar 14, 2005 at 4:16 AM

std::ostream& operator<<(std::ostream& ls, const std::string& rs){    return ls << rs.c_str();}

Is how you make it work with std::string.
Or you can generalize that like I do:

template<typename _Elem, typename _Traits, typename _Ax>std::basic_ostream<_Elem, _Traits>& operator<<(  \         std::basic_ostream<_Elem, _Traits>& ls,  \         const std::basic_string<_Elem, _Traits, _Ax>& rs){	return ls << rs.c_str();}

Which of course makes it work with std::ofstream, std::wcout, std::wofstream, std::wstring, etc., so long as the elements and traits match (it gets wonky if they don't, which is why the template forbids them from being different)

Try:

template<class T>Console& operator<<(Console& ls, T& rs){    ls.Write(rs);    return ls;}

If the Write code you posted worked (which it shouldn't since console was mispelled and you're outputting the type rather than the variable), then this should work.

Edit:
I notice in your OP you said "pointers to cin and cout", so "console.outstream" is a std::ostream*? If so, then a problem (if not the problem) was that you're doing a shift operation on the pointer. You should dereferanced the pointer, so it would look something like this:

class Console{    //...    std::ostream* outstream;    //...    Console()    {    //...        outstream = &std::cout;    //...    }    //...};//...template<class T>Console& operator<<(Console& ls, T& rs){    (*ls.outstream) << rs;    return ls;}

[Edited by - Erzengeldeslichtes on March 14, 2005 5:16:30 AM]

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.