- Typically, the underscore is used in front of member variables in a class, to distinguish them (for the reader) from local variables. The presence or absence of the _ (or __) makes no difference to the compiler.
- In C++, an underscore usually indicates a private member variable.
- Names beginning with an underscore or a double underscore are RESERVED for the C++ implementers. Names with an underscore are reserved for the library to work.