Trouble with overloading the '==' operator

[Ryeman]

Here's the problem I'm having - I need to overload a class operator '==' so that I can compare multiple class variables in one evaluation. In my case, I need to compare 4 class variables. Here's what I've got:

Class declaration:
const bool& Class::operator == (const Class&);

Usage:
Class a, b, c, d;

if (a == b == c == d)

The compiler only allows me:

if ((a == b) && (a == c) && (a == d) && (b == c) && (b == d) && (c == d))

This seems really sloppy, and wouldn't be feasible to compare a large number of values. I can't declare multiple arguments for '==', such as:

const bool& Class::operator == (const Class&, const Class&);

Is there another way to assign the '==' operator or overload it?

[firedraco]

Nope. I suppose you could put them all into a set and check to make sure there is only one value in the set.

Btw, you can shorten your if statement to:
if((a==b) && (b==c) && (c==d))

[Ryeman]

Update:

The compiler also does not allow:

if ((a == b) && (a == c) && (a == d) && (b == c) && (b == d) && (c == d))

As soon as I introduce the (b == c), it says that 'no operator && matches these operands'.

I think I am understanding that I am mixing operators between separate classes variables now, but how do I fix it?

[firedraco]

I think you screwed something else up, that looks fine. The () should force the correct precedence (if it isn't correct already).

[Ryeman]

Thanks, firedraco, the statement:

if((a == b) && (b == c) && (c == d))

works just fine! However, I am curious that the compiler suggested:

error C2678: binary '==' : no operator found which takes a left-hand operand of type 'bool' (or there is no acceptable conversion)
could be 'bool std::operator ==(const std::_Exception_ptr &,const std::_Exception_ptr &)'
or 'bool std::operator ==(std::_Null_type,const std::_Exception_ptr &)'
or 'bool std::operator ==(const std::_Exception_ptr &,std::_Null_type)'
or 'bool std::operator ==(const std::error_code &,const std::error_condition &)'
or 'bool std::operator ==(const std::error_condition &,const std::error_code &)'

Why does it suggest multiple argument 'bool std::operator ==' operators?

[coder777]

this const bool& Class::operator == (const Class&, const Class&); returns bool.

an if statement like if(a == b == c) would resolve to if(operator==(a, b) == c) So c is compared whith bool which probably doesn't work

[Syuf]

const bool& Class::operator == (const Class&);
You return a reference to a local variable.
Do so:
bool Class::operator == (const Class&) const;
And some notes:
1) Don't use notation const T& with basic integral types.
2) Always match const or/and valotatile specifiers to non-static member functions, when it's possibly.

[Ryeman]

Thanks for the tips, everyone! I have worked around this issue, but I will still continue to wonder. Standard types and constants can compare multiple variables just fine, as in:

int a, b, c, d;

if(a == b == c == d)

or:
if(1 == 2 == 3 == 4)

The compiler even allows different types to be compared (with obvious warnings, of course):

char a;
int b;
float c;
double d;

if(a == b == c == d)

My solution was:

Class a, b, c, d;

if((a == b) && (b == c) && (c == d))

as suggested by firedraco.

[coder777]

This if(1 == 2 == 3 == 4) resolves to if(((1 == 2) == 3) == 4) // if this is the order -> if((0 == 3) == 4) -> if(0 == 4)