Function: buffer-file-name
buffer-file-name is a function defined in buffer.c.
Signature
(buffer-file-name &optional BUFFER)
Documentation
Return name of file BUFFER is visiting, or nil if none.
No argument or nil as argument means use the current buffer.
Probably introduced at or before Emacs version 17.
Source Code
// Defined in /usr/src/emacs/src/buffer.c
{
return BVAR (decode_buffer (buffer), filename);
}