What are the Operators that Can be and Cannot be Overloaded in C++?
There are various ways to overload Operators in C++ by implementing any of the following types of functions:
1) Member Function
2) Non-Member Function
3) Friend Function
List of operators that can be overloaded are:
+ | – | * | ⁄ | % | ‸ | & | | | ~ |
! | = | < | > | += | -= | *= | ⁄= | %= |
‸= | &= | |= | << | >> | <<= | >>= | == | != |
<= | >= | && | || | ++ | — | , | ->* | -> |
( ) | [ ] | new | delete | new[] | delete[] |
|
Example 1: Overloading ++ Operator
CPP
// CPP program to illustrate // operators that can be overloaded #include <iostream> using namespace std; class overload { private : int count; public : overload() : count(4) { } void operator++() { count = count + 1; } void Display() { cout << "Count: " << count; } }; int main() { overload i; // this calls "function void operator ++()" function ++i; i.Display(); return 0; } |
Count: 5
This function is called when the ++ operator operates on the object of the overload class (object i in this case). In the program, void operator ++ () operator function is defined (inside overload class). This function increments the value of count by 1 for i object.
Example 2: Overloading ++ operator i.e. pre and post increment operator
CPP
// CPP program to demonstrate the // Difference between pre increment // and post increment overload operator #include <iostream> using namespace std; class overload { private : int count; public : overload( int i) : count(i) { } overload operator++( int ) { return (count++); } overload operator++() { count = count + 1; return count; } void Display() { cout << "Count: " << count << endl; } }; // Driver code int main() { overload i(5); overload post(5); overload pre(5); // this calls "function overload operator ++()" function pre = ++i; cout << "results of I = " ; i.Display(); cout << "results of preincrement = " ; pre.Display(); // this call "function overload operator ++()"function i++; // just to show diff i++; // just to show diff post = i++; cout << "Results of post increment = " ; post.Display(); cout << "And results of i , here we see difference : " " " ; i.Display(); return 0; } |
results of I = Count: 6 results of preincrement = Count: 6 Results of post increment = Count: 8 And results of i , here we see difference : Count: 9
Example 3: Overloading [ ] operator
CPP
// CPP program to illustrate overloading the // [ ] operator #include <iostream> using namespace std; class overload { int a[3]; public : overload( int i, int j, int k) { a[0] = i; a[1] = j; a[2] = k; } int operator[]( int i) { return a[i]; } }; int main() { overload ob(1, 2, 3); cout << ob[1]; // displays 2 return (0); } |
2
Example 4 : Overloading -> operator
CPP
// CPP program to illustrate // operators that can be overloaded #include <bits/stdc++.h> using namespace std; class GFG { public : int num; GFG( int j) { num = j; } GFG* operator->( void ) { return this ; } }; // Driver code int main() { GFG T(5); GFG* Ptr = &T; // Accessing num normally cout << "T.num = " << T.num << endl; // Accessing num using normal object pointer cout << "Ptr->num = " << Ptr->num << endl; // Accessing num using -> operator cout << "T->num = " << T->num << endl; return 0; } |
T.num = 5 Ptr->num = 5 T->num = 5
List of operators that cannot be overloaded
1) Scope Resolution Operator (::)
2) Ternary or Conditional Operator (?:)
3) Member Access or Dot operator (.)
4) Pointer-to-member Operator (.*)
5) Object size Operator (sizeof)
6) Object type Operator(typeid)
7) static_cast (casting operator)
8) const_cast (casting operator)
9) reinterpret_cast (casting operator)
10) dynamic_cast (casting operator)
Example 5: Overloading this .(dot) operator
Dot (.) operator can’t be overloaded, so it will generate an error.
CPP
// C++ program to illustrate // Overloading this .(dot) operator #include <iostream> using namespace std; class cantover { public : void fun(); }; class X { cantover* p; cantover& operator.() { return *p; } void fun(); }; void g(X& x) { x.fun(); // X::fun or cantover::fun or error? } |
Output: Error
prog.cpp:12:23: error: expected type-specifier before ‘.’ token cantover& operator.() { return *p; }
This program will generate an error. Similarly, the above operators will also generate an error, if overloaded.
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