What's the meaning of #line in C language?

Question

What\'s the meaning of #line in the C language? Where would it be used?

Answer 1

It is mostly used to supply the file names and line numbers of a source file from which a C file (be it header or implementation) was created. Given that, the compiler would emit diagnostics that hint at the source file rather than at the generated file.

Preprocessors also use this to hint at included headers in a preprocessed file that has these expanded.