The result is a Number, which is the byte index of the column position given with {expr}. The accepted positions are: . the cursor position $ the end of the cursor line (the result is the number of bytes in the cursor line plus one) 'x position of mark x (if the mark is not set, 0 is returned) v In Visual mode: the start of the Visual area (the cursor is the end). When not in Visual mode returns the cursor position. Differs from '< in that it's updated right away. Additionally {expr} can be [lnum, col]: a List with the line and column number. Most useful when the column is "$", to get the last column of a specific line. When "lnum" or "col" is out of range then col() returns zero. With the optional {winid} argument the values are obtained for that window instead of the current window. To get the line number use line(). To get both use getpos(). For the screen column position use virtcol(). For the character position use charcol(). Note that only marks in the current file can be used. Examples:

col(".")                column of cursor
col("$")                length of cursor line plus one
col("'t")               column of mark t
col("'" .. markname)    column of mark markname

The first column is 1. Returns 0 if {expr} is invalid or when the window with ID {winid} is not found. For an uppercase mark the column may actually be in another buffer. For the cursor position, when 'virtualedit' is active, the column is one higher if the cursor is after the end of the line. Also, when using a <Cmd> mapping the cursor isn't moved, this can be used to obtain the column in Insert mode:

:imap <F2> <Cmd>echowin col(".")<CR>

Can also be used as a method:

GetPos()->col()