I write a short macro which put a picture on the left and a text on the right:
\newlength\largeur
\newcommand{\uneQuestion}[1]{
\setlength{\largeur}{\columnwidth}
\addtolength{\largeur}{-16mm}
\noindent
\hspace*{2mm}
\parbox{12mm}{\iconequestion}
\hspace*{2mm}
\parbox{\largeur}{\color{CouleurQuestion!95} #1}
}
As you can see largeur will be the width of the text and in order to compute it, I substract to the column width the two \hspaces and the \parbox space.
But If I did that, the text is slightly larger than the \columnwidth. I guess that there is a short space around a \parbox?
\hspaces and both\parboxes), which is removed when you end the line with%. See What is the use of percent signs (%) at the end of lines? – Werner Jan 16 '14 at 15:29