what is #line

i want to know more about #line in cpp. is it is a preprocessor..?what action it will do...?

It's a preprocessor/compiler instruction that tells the compiler what line it is on, overriding its internal count. It's used mostly by tools that generate C or C++ code, such as lex and yacc, so that error messages from the compiler relate back to the original source file, not the generated code.