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Overloading operators outside of class

Posted on 2009-05-19
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Last Modified: 2013-12-14
Experts,
 I am trying to write implementation files for my class headers and in these implementation files, I want to overload certain operators. I am getting errors like:
 '<' : is not a member of 'C_Aircaft AND:
 '==' : modifiers not allowed on nonmember functions      

Below is a copy of the class declarator and the relevant section of the implementation file - any clues?

Thanks



======================CLASS DECLARATOR======================
friend bool operator < (const C_Aircraft& a1, const C_Aircraft& a2)const;	// Operator overload declarator
'===================IMPLEMENTATION CPP FILE========================
bool C_Aircraft::operator < (const C_Aircraft& a1, const C_Aircraft& a2)const
{
                                         if(a1.model==a2.model)
		return(a1.callsign<a2.callsign)?true:false;
		return (a1.model<a2.model)?true:false;
}

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Question by:simondopickup
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2 Comments
 
LVL 86

Accepted Solution

by:
jkr earned 500 total points
ID: 24423695
A non- member operator cannot be declared as 'const' (at least that makes no sense). Also, the global operator cannot be defined at class scope. So, try
// foward declaration
 
operator < (const C_Aircraft& a1, const C_Aircraft& a2);
 
class C_Aircraft
{
 
friend bool operator < (const C_Aircraft& a1, const C_Aircraft& a2);       // Operator overload declarator
 
// rest of declaration
 
};
 
// implementation
bool operator < (const C_Aircraft& a1, const C_Aircraft& a2)
{
         if(a1.model==a2.model)
                return(a1.callsign<a2.callsign)?true:false;
 
         return (a1.model<a2.model)?true:false;
}

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Author Closing Comment

by:simondopickup
ID: 31583077
Excellent, thanks JKR
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