在使用gcc編譯代碼時出現了一個warning，no newline at end of file ，具體原因是因為在文件尾必須的新增一行空行，以避免include文件時，展開后與后面的文件連為一行，造成錯誤。C++文檔中有明確說名。唉，vs就從來沒有提醒過，難道是換行符的區別？
A source file that is not empty and that does not end in a new-line character, or that ends in a new-line character immediately preceded by a backslash character before any such splicing takes place, shall be processed as if an additional new-line character were appended to the file (C++11 §2.2/1)