How to show 80-character column line in Texmaker?

Alternative solution (another editor)

If you wish you can try another editor. TeXstudio is very good and powerful and it is based on TeXmaker. So you will not change so much what you know.

TeXstudio allows you to determine the number of characters for wrapping lines and also how to wrap.

See the Configure for Advanced Editor options (note the Show Advanced Options checked on the left bottom corner):

According to the release notes TexMaker (> Version 4.4) is using a script to hardwrap your code. This script needs to be triggered manually as shown below (Menu: User -> Run Script, unfortnately I have a German system only).

However, TexMaker does not have any functionality to do this automatically or to show the desired 80-char-line as stated here.