error C2678: binary '<'

Hi All,

I am carrying out operator overload for a class - ErrorType and I am getting this error on compiling ErrorType.cpp:

errortype.cpp(43) : error C2678: binary '<' : no operator found which
takes a left-hand operand of type 'const ErrorType' (or there is no
acceptable conversion)

Here is the portion of code:

Code:

---

bool ErrorType::operator<(const ErrorType& right)
{
if((priority < right.priority)||
(priority == right.priority &&
timestamp < right.timestamp)||
(priority == right.priority &&
timestamp == right.timestamp &&
errorCode < right.errorCode))
return true;
else
return false;
}


bool ErrorType::operator>(const ErrorType& right)
{
return right < *this; //line 43
}

---

I will appreciate any assistance.

Chike.

> return right < *this; //line 43
I think it should be:
return *this < right;

Although I don't quite understand why. :confused:

Quote:

---

Originally Posted by swoopy

> return right < *this; //line 43
I think it should be:
return *this < right;

Although I don't quite understand why. :confused:

---

The parameter right was declared const. That means the object is const inside the operator function. But, const objects can only call const member functions because const objects must have a guarantee that they won't be changed. Since the operator<() function wasn't defined as const, e.g.

Code:

---

bool ErrorType::operator<(const ErrorType& right) const

---

a const object can't call the function. The reason is that every class method has an invisible parameter: the this pointer. The this pointer can implicity or explicity be used inside the function to change the object, e.g.:

setPrivateVar(10);

or

this->setPrivateVar(10);

When you declare a member function const, the compiler will ensure that no changes can be made to the calling object.

Thank you Swoopy,

You got it. Although I had resolved the problem anoter way by removing the "const" qualifiers (which is against my design of making the members (arguments) unmodifiable. So now I went and read this up again at the msdn site and have now inserted back the "const" qualifiers and made the member functions const functions.

Thanks a lot fo your very detailed explanation. I understand this better now.

Chike.

Quote:

---

Originally Posted by 7stud

Since the operator<() function wasn't defined as const, e.g.

Code:

---

bool ErrorType::operator<(const ErrorType& right) const

---

a const object can't call the function. The reason is that every class method has an invisible parameter: the this pointer. The this pointer can implicity or explicity be used inside the function to change the object, e.g.:

setPrivateVar(10);

or

this->setPrivateVar(10);

---

Ok, that makes sense. 7stud, thanks for the thorough explanation.