LaTeX: to get the current position in line

bxposinline.sty

% bxposinline.sty

%% declaration
\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{bxposinline}[2016/01/23 v0.2]
\def\bxqpi@pkgname{bxposinline}

%% package
\RequirePackage{zref-savepos}

%--------------------------------------- main

%% variables
\newcount\bxqpi@id
\newdimen\bxqpi@indent
\newdimen\bxqpi@lwidth
\newdimen\bxqpi@offset
\let\bxqpi@label\relax

%%<+> \PILLeft/\PILRight
\newdimen\PILLeft
\newdimen\PILRight

%%<+> \GetPositionInLine
\protected\def\GetPositionInLine{%
  \leavevmode \@bsphack
  % do zsavepos
  \bxqpi@gen@label
  \zsavepos{\bxqpi@label C}%
  \vadjust{\hbox{\zsavepos{\bxqpi@label L}}}%
  % 
  \ifnum\zposx{\bxqpi@label C}=\z@ % no previous data
    \PILLeft=-\maxdimen \PILRight=-\maxdimen
  \else
    % get paragraph parameters
    \ifnum\parshape=\@ne % in LaTeX list environment
      \bxqpi@indent=\parshapeindent\@ne\relax
      \bxqpi@lwidth=\parshapelength\@ne\relax
    \else
      \bxqpi@indent=\z@ \bxqpi@lwidth=\hsize
    \fi
    % calculate the positions
    \PILLeft=\dimexpr
      \zposx{\bxqpi@label C}sp-\zposx{\bxqpi@label L}sp
      -\bxqpi@indent\relax
    \PILRight=\dimexpr
      \bxqpi@lwidth-\PILLeft\relax
  \fi
  \@esphack}

%% \bxqpi@gen@label
\def\bxqpi@gen@label{%
  \global\advance\bxqpi@id\@ne
  \edef\bxqpi@label{bxqpi:\the\bxqpi@id}}

%--------------------------------------- done
\endinput
%% EOF

test-bxposinline.tex

\documentclass[a4paper,twocolumn]{article}
\usepackage{bxposinline}
\def\?{\GetPositionInLine
  \typeout{\the\PILLeft/\the\PILRight}}
\begin{document}

\?Lorem ipsum dolor \?sit amet,
consectetuer adipiscing elit.
Ut purus elit, vestibulum ut, placerat ac,
adipiscing vitae, felis.\?
Curabitur dictum\? \?gravida mauris.\?

\begin{itemize}
\item \?Nam arcu libero, nonummy eget,
  consectetuer\? id, vulputate a, magna.
  Donec vehicula augue \?eu neque.\?
\item Pellentesque habitant morbi tristique senectus et netus
  et malesuada fames ac turpis egestas.
\end{itemize}

\parbox{100pt}{%
  \?Mauris ut leo.
  Cras\? \?viverra metus rhoncus sem.\?
  Nulla et lectus vestibulum urna fringilla ultrices.
}

\end{document}

When \GetPositionInLine is called, the length variable \PILLeft (or \PILRight) is set the hotizontal distance between the current reference point and the beginning (or end, resp.) of the current line.