what is the meaning of "\015\012" ? is it same with "\r\n"?

The \015\012 means "CR-LF", a carriage-return character followed by a line-feed character.

The \r\n is intended to produce the same results, but the value of \n can change depending on your operating system, so for network protocols where you specifically mean to send CR-LF, the \015\012 sequence is your best bet.

by the way, what is the meaning of \r? i know that \n means go to next line.

A long time ago, on a minicomputer line printer far far away, a CR shifted the print head all the way back to the left end of the line, and LF shifted it down one line, thus the names carriage return and line feed. Modern systems use either one or the other, or both, to separate lines of text.