How to set the default width of fill mode to 80 with emacs?

I know that "C-u 80 C-x f" sets the fil开发者_C百科l width 80, and M-q adjusts it. How to make it default? I mean, how to make width 80 deafault for fill width?

In your .emacs place (setq-default fill-column 80) Or you can just use M-x customize-variable on fill-column, and it will set it and save it for you using the standard customize interface.