In C++, which of the following operator cannot be overloaded ?

Question

Accepted Answer

The correct option is (3):
The operator that cannot be overloaded in C++ is the member selection operator, denoted by the dot symbol (.). This rule is in place to preserve the fundamental integrity and built-in meaning of C++'s object model and syntax. The dot operator is crucial for accessing the actual members (variables or functions) of a class object, and allowing its behavior to be modified could lead to ambiguous and unsafe code, essentially "breaking" the core mechanism of class member access. The C++ standard explicitly prohibits the overloading of a small set of operators, including `.` (member access), `::` (scope resolution), `?:` (ternary conditional), and `.*` (pointer-to-member access), as their inherent behavior is fundamental to the language structure and is handled directly by the compiler. Attempting to define an overload for the dot operator will always result in a compilation error.

The incorrect option is (1):
The caret operator, `^`, which is the bitwise XOR operator, can be fully overloaded in C++ for user-defined types. This is commonly done to define a logical XOR operation or to implement a custom bitwise operation for a class, such as a specialized set or key class. The flexibility of overloading arithmetic and bitwise operators like `^` allows developers to extend their functionality to complex data types, making the code more intuitive and readable by using standard mathematical notation. It can be overloaded as either a member function or a non-member function.

The incorrect option is (2):
The equality operator, `==`, is one of the most frequently overloaded operators in C++. It is a binary relational operator used to define a custom comparison logic between two objects of a user-defined class. For a custom class, the built-in `==` would only compare the memory addresses, which is rarely the desired behavior for complex objects. By overloading `==`, a programmer defines what "equal" means for their objects—for example, comparing all member values—which is vital for using custom objects in standard library containers and conditional statements.

The incorrect option is (4):
The logical NOT operator, `!`, is a unary operator that is perfectly capable of being overloaded in C++. Overloading `!` is often employed to define what it means for an object of a user-defined class to be logically 'false' or 'not true'. For instance, in a custom `File_Handle` class, overloading `!` could be used to check if the file is not currently open or if an error has occurred. It provides a clean, idiomatic way to negate an object's state, returning a boolean result, and is part of the set of unary operators designed for extension.