Why clog is used in c++ !!!

Answer 1

http://www.cplusplus.com/reference/iostream/clog/
https://www.programiz.com/cpp-programming/library-function/iostream/clog

Answer 2

C++ clog. The clog object in C++ is an object of class ostream. It is associated with the standard C error output stream stderr. clog and cerr , both are associated with stderr , but it differs from cerr in the sense that the streams in clog are buffered and not automatically tied with cout .