Besides 'new', 'delete', '<<' & '>>' operators, what other operators can be overloaded in C++ outside of a class context?
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1Outside of class context meaning, not inside a class but still involves a class object in arguments or a class return typeMurali VP– Murali VP2009-09-19 14:04:26 +00:00Commented Sep 19, 2009 at 14:04
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2 Answers
The following operators (delimitted by space) can be overloaded as non-member functions:
new delete new[] delete[] + - * / % ˆ & | ˜ ! < > += -= *= /= %= ˆ=
&= |= << >> >>= <<= == != <= >= && || ++ -- , ->*
The following have to be non-static member functions:
-> () [] =
The following can not be overloaded:
. .* :: ?: # ##
conversion operators also have to be member functions.
And just because it has a '=' in it does not mean it cannot be overloaded as a non-member operator. The following is well-formed:
struct A { };
A operator +=(A,A) { return A(); }
A a = A()+=A();
And the prefix and postfix increment and decrement operators can indeed be defined as non-members:
13.5.7 The user-defined function called operator++ implements the prefix and postfix ++ operator. If this function is a member function with no parameters, or a non-member function with one parameter of class or enumeration type, it defines the prefix increment operator ++ for objects of that type. If the function is a member function with one parameter (which shall be of type int) or a non-member function with two parameters (the second of which shall be of type int), it defines the postfix increment operator ++ for objects of that type. When the postfix increment is called as a result of using the ++ operator, the int argument will have value zero.
The prefix and postfix decrement operators -- are handled analogously
Clause 13.5 in the Standard covers this.
Hope this helps.
2 Comments
sbk
Nitpicking: Operator +=, similar to operator = and pretty much anything with = in it, should return an lvalue. I'd rewrite your operator definition like this: A& operator += (A&, A) { ... }. Your other line won't compile then, but A() += A() is a little bit counter-intuitive, applying += on temporary is useless (not to mention that conforming C++ compiler won't accept it)
Faisal Vali
@sbk Thanks for the feedback - the fragment was not supposed to be an example of "good" operator overloading style - but was intended to indicate that overloading such operators (@=) as non-member functions is valid - and you're wrong about conforming compilers not accepting the fragment as well formed code - it is syntactically valid - semantically it is a bad idea - but not only does the standard say little about what the semantics of overloaded operators should be - semantics and good style were not the focus of my answer nor the OP's question ;)
Operators that can be overloaded (comma used as delimiter):
+, -, *, /, %, ^, &, |, ~, !, =, <, >, +=, -=, *=, /=, %=, ^=, &=, |=, >>=, <<=,
!=, <=, >=, &&, ||, ++, --, ->* , (i.e., comma operator), ->, [], (), new[], delete[]
Operators that can not be overloaded:
., .*, ::, ?:
Operators where overloading function must be declared as a class method:
(), [], ->, any assignment operator
(as the commenters noted)
6 Comments
Murali VP
Thanks for the quick response, but the question specifically asks for which of these can be overloaded outside of a class
Murali VP
Not at all, for example, try overloading operator ++ outside a class.
eduffy
The question asked for operators that aren't class methods. So anything with an
= and the ->, [], and () operators don't belong.
Edu Felipe
No. You can't override
-> outside of a class.
Konrad Rudolph
Don’t forget conversion operators (only inside classes, though)!
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