What is a user defined manipulator in c plus plus?

Answer 1

A user-defined manipulator is a function which can be passed as an argument to the stream insertion or extraction operator overloads. For example, the output stream insertion operator has the following overload:

std::ostream& operator<< (std::ostream& st, std::ostream& (*func) (std::ostream&));

The second argument is the function pointer, with the following signature:

std::ostream& (*func) (std::ostream&)

Any function that matches this signature can be used as a manipulator. For instance, the following user-defined manipulator does exactly the same job as the std::endl manipulator:

std::ostream& my_manipulator (std::ostream& os)

{

return os << '\n' << std::flush;

}

Example usage:

std::cout << "Hello world!" << my_manipulator;

You can, of course, provide your own implementations to perform any type of manipulation. For example, suppose you want a manipulator that inserts an elipses into an output stream:

std::ostream& elipses (std::ostream& os)

{

return os << "...";

}

Example usage:

std::cout << "Hello" << elipses << "world!" << my_manipulator;

Output:

Hello...world!