Which operators cannot be overloaded in C++?
There are some operators in C++ that cannot be overloaded like as follows:
The ?: (ternary conditional operator) in C++ cannot be overloaded. This operator is a conditional operator that takes three operands and returns the second or third operand based on the evaluation of the first operand. Since this operator is built into the language and has a fixed syntax and behaviour, it cannot be redefined or overloaded like other operators in C++.
In addition to the (?:) operator, there are a few other operators in C++ that cannot be overloaded.
These include the scope resolution operator::, the member selection operator .*, the pointer-to-member operator ->*, and the sizeof operator.
- The scope resolution operator (::) is used to qualify a name with a namespace, class, or enumeration scope. Since the behaviour of this operator is built into the language and is essential for specifying the scope of a name, it cannot be overloaded.
- The member selection operator (.*) and the pointer-to-member operator ->* are used to access members of a class through a pointer to a class object or a pointer to a class member, respectively. These operators are also essential to the language and cannot be overloaded.
- The sizeof operator is used to determine the size of a type or object. Since this operator is evaluated by the compiler and not at runtime, it cannot be overloaded.
Overall, the C++ language specification defines which operators can and cannot be overloaded. While most operators can be overloaded to provide custom behaviour for user-defined types, certain operators have fixed behaviour that cannot be changed through operator overloading.
Why these operators cannot be overloaded?
The operators that cannot be overloaded in C++ are typically fundamental to the language's syntax and semantics and have well-defined behaviour that cannot be changed through operator overloading. These operators are either essential for working with object-oriented programming constructs in C++ or provide information that is evaluated by the compiler rather than at runtime.
Overloading these operators could potentially introduce ambiguity or unexpected behaviour, making it difficult for programmers to write clear and maintainable code. Additionally, since these operators are built into the language and have a fixed syntax, overloading them would require significant changes to the language's underlying implementation.
For example, the (::) operator is used to specify the scope of a name and is essential for resolving name conflicts and accessing members of classes or namespaces. Since this operator is built into the language and its behaviour is fundamental to the syntax and semantics of C++, it cannot be overloaded.
Overall, while it may be possible to overload some of these operators in theory, doing so could have significant implications for the language's syntax and semantics, making it more difficult for programmers to write clear and maintainable code. As a result, the C++ language specification defines which operators can and cannot be overloaded, providing a clear and consistent framework for working with operator overloading in C++.
Example:
Here's an example to illustrate why overloading the scope resolution operator :: in C++ could be problematic.
The :: operator is used to qualify a name with a namespace, class, or enumeration scope. For example, in the following code, the :: operator is used to access the cout object defined in the std namespace:
#include <iostream>
Using namespace std;
int main() {
std::cout<< "Hello, world!" <<std::endl;
return 0;
}
Output:
Hello, world!
If we were to overload the :: operator, we would be changing the way that names are qualified with namespaces, classes, or enumerations. This could potentially introduce ambiguity or unexpected behavior, making it difficult for programmers to write clear and maintainable code.
For example, let's say we defined a custom :: operator that reversed the order of the operands and returned the first operand:
int operator::(int a, int b) {
return a;
}
Now, when we try to use the std::cout object in the previous example, we would get a compile-time error, since the :: operator is no longer performing namespace qualification as expected:
Example:
#include <iostream>
int operator::(int a, int b) {
return a;
}
int main() {
std::::cout<< "Hello, world!" <<std::endl;
// Compile-time error: expected primary-expression before '::' token
return 0;
}
This example illustrates how overloading an essential operator like :: can lead to unexpected behaviour and make it more difficult for programmers to write clear and maintainable code. As a result, the :: operator is not over loadable in C++.