Question

The following errors are always been pointing to my List.

In my class file

Point3D operator==(const Point3D &p1) const;

In my .cpp file

bool operator==(Point3D &p1, Point3D &p2)
{
    if ( p1.getX() == p2.getX() && p1.getY() == p2.getY() && p1.getZ() == p2.getZ() )
        return true;
    else
        return false;
}

In my main file

//declaration
list<Point3D> l_3D;

l_3D.unique(); <-- the error point to this 

Error message

..... In member function 'void std::list<_Tp,_Alloc>::unique() [with_Tp = Point3D,_Alloc = std:: allocator<Point3D>]:

Instantiated from here

error: could not convert 'Point3D::operator==(const Point3D&) const (((const Point3D&)((const Point3D*)__next. std::_List_iterator<_Tp>::operator*[with_Tp = Point3D]())))' to 'bool'

To the kind souls out there, I thank you in advance.

Answer 1

In your declaration you return Point3D, which should be bool:

Point3D operator==(const Point3D &p1) const;
^^^^^^^
should be bool

The above looks like you declare the operator as a member-function, bet then you implement it as a free function. You have to decide which it is. If you use a member-function, change the implementation to:

bool Point3D::operator==(const Point3D &p2) const
{
    if ( getX() == p2.getX() && getY() == p2.getY() && getZ() == p2.getZ() )
        return true;
    else
        return false;
}

Or even better (as per @ibids comment):

bool Point3D::operator==(const Point3D &p2) const
{
    return (getX() == p2.getX() && getY() == p2.getY() && getZ() == p2.getZ());
}

Generally the signature of your definition should match the signature of your declaration.