Problem when comparing deques

Question

2.00/5 (2 votes)

See more:

I'm having some difficulties when trying to comapare two deques of a selfmade struct.
This is my struct and the deque declaration:

C++

class iterator
{
public:
struct PosPtrs
{
    NodeLevel Level;
    TreeElement Element;
    bool operator ==(const PosPtrs& input)
    {
        return Level == input.Level && Element == input.Element;
    }
    bool operator== (PosPtrs& input)
    {
        return Level == input.Level && Element == input.Element;
    }
};
std::deque<PosPtrs> TreeHistory;
private:
....
};

When Trying

C++

iterator it1;
iterator it2;
return it1.TreeHistory == it2.TreeHistory;

I get a compiler error C2678:

d:\program files\microsoft visual studio 10.0\vc\include\xutility(2990):error C2678: binary '==' : no operator found which takes a left-hand operand of type 'const BaseTree::iterator::PosPtrs' (or there is no acceptable conversion)
1> d:\program files\microsoft sdks\windows\v7.0a\include\guiddef.h(192): could be 'int operator ==(const GUID &,const GUID &)' [found using argument-dependent lookup]
1> d:\program files\microsoft visual studio 10.0\vc\include\exception(470): or 'bool std::operator ==(const std::_Exception_ptr &,const std::_Exception_ptr &)'
1> d:\program files\microsoft visual studio 10.0\vc\include\exception(475): or 'bool std::operator ==(std::_Null_type,const std::_Exception_ptr &)'
1> d:\program files\microsoft visual studio 10.0\vc\include\exception(481): or 'bool std::operator ==(const std::_Exception_ptr &,std::_Null_type)'
1> d:\program files\microsoft visual studio 10.0\vc\include\system_error(408): or 'bool std::operator ==(const std::error_code &,const std::error_condition &)'
1> d:\program files\microsoft visual studio 10.0\vc\include\system_error(416): or 'bool std::operator ==(const std::error_condition &,const std::error_code &)'
1> d:\users\maxime\documents\visual studio 2010\projects\regfilehook\regfilehook\xmlfilereadwrite.h(156): or 'bool BaseTree::iterator::PosPtrs::operator ==(const BaseTree::iterator::PosPtrs &)'
1> d:\users\maxime\documents\visual studio 2010\projects\regfilehook\regfilehook\xmlfilereadwrite.h(160): or 'bool BaseTree::iterator::PosPtrs::operator ==(BaseTree::iterator::PosPtrs &)'
1> while trying to match the argument list '(const BaseTree::iterator::PosPtrs, const BaseTree::iterator::PosPtrs)'
1> ....

The last lines are confusing me. The compiler tries to match an argument list of a operator++() function with 2 arguments? I tought an operator== was always defined with only one argument (trying this doesn't helps either, it ends like expected in a compiler error)..

Thanks in Advance

Posted 21-Aug-12 7:57am

MXT3

Updated 21-Aug-12 9:24am

v3

Add a Solution

Comments

Sergey Alexandrovich Kryukov 21-Aug-12 14:06pm

Always indicates the line(s) related to the compiler error message in the source code sample. Do you like people to waste time?
--SA

Sergey Alexandrovich Kryukov 21-Aug-12 14:08pm

How a binary infix operator ("==" or some other) can "one argument"?! The problem is not that you don't know something; I'm just curious what was your thinking?
--SA

MXT3 21-Aug-12 15:11pm

If you take for instance two int a and b; then "a == b" is the same as "a.operator==(b)", or not?

Sergey Alexandrovich Kryukov 21-Aug-12 16:37pm

That's too parameters, a and b. You think in a.Operator syntax a is something special, but this is just another parameter. "==" is binary.
In C++, the operator's function is a non-static (instance) function (in some other systems, the developers supplied static function with two parameters, one must be of the same class), but the mechanism of some function is passing, say, a and a hidden/implicit parameter to the function as a regular parameter. Inside implementation, this parameters is accessible as "this". Are you getting the idea..?
--SA

MXT3 22-Aug-12 4:39am

Yes "a" is nothing special, it's the parent of it's operator== function and is passed as a implicit parameter. The words " argument list (const BaseTree::iterator::PosPtrs, const BaseTree::iterator::PosPtrs)" just confused me because it looked like the compiler was looking for two explicit parameters, now I know the first one is implicit, and that it had to be passed const

Sergey Alexandrovich Kryukov 22-Aug-12 11:25am

Are you unconfused now? :-)
--SA

MXT3 22-Aug-12 14:39pm

yes, thank you :)

Sergey Alexandrovich Kryukov 22-Aug-12 17:49pm

Great! Good luck, call again.
--SA

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

JackDingler · Accepted Answer · 2012-08-21T09:33:00

C++

class iterator
{
public:
struct PosPtrs
{
    NodeLevel Level;
    TreeElement Element;
    bool operator ==(const PosPtrs& input) const
    {
        return Level == input.Level && Element == input.Element;
    }
};
std::deque<posptrs> TreeHistory;
private:
....
};

The clue comes from this message:
d:\program files\microsoft visual studio 10.0\vc\include\xutility(2990):error C2678: binary '==' : no operator found which takes a left-hand operand of type 'const BaseTree::iterator::PosPtrs' (or there is no acceptable conversion)

Your left hand operand needs to be const also.