Working of errno in C++

The errno works as the explain below:

• Initially at the beginning of the program, the errno is set to zero and it changes when any error occurs.
• If a function call fails it sets errno, then we check its value. There is no change in the value errno if no errors occur.

In C++ errno is a preprocessor macro that is used for error indication and reporting errors that occur during a function call. It contains error codes so if a call to a function fails somehow then the errno is set to a value that corresponds to the error.

errno is defined in the header file <cerrno> in C++.