Compare Variables

Question

I want to have a macro that checks if the string has been used in the previous call of the macro as well. I found some examples here how to create switch structure comparing strings in latex but I wasn't able to store and retrieve the value in a variable. What can I do to make this code work?

\documentclass{article}
\usepackage{pdftexcmds}

\def \myoldvalue {emptystart}

\makeatletter
\newcommand\foo[1]{%
 \\myoldvalue: \myoldvalue  \def \myoldvalue {#1} \newline %
 ARG1: #1 \newline %
   \def\@tempa{#1}%
   \def\@tempb{comparetothis}% % what do I have to put into comparethis to compare against \myoldvalue
   compare: \@tempa ~ \@tempb \newline %
 \begingroup
    \@onelevel@sanitize\@tempa
    \@onelevel@sanitize\@tempb
    \ifx\@tempa\@tempb
       \aftergroup\@firstoftwo
    \else
      \aftergroup\@secondoftwo
    \fi
  \endgroup
    {TRUE}
    {FALSE}%
    \newline next old value: \myoldvalue
}
\makeatother
\begin{document}
~\\
\foo{ArgOne} \\ % excepted print out is: FALSE
\foo{ArgOne} \\ % TRUE
\foo{ArgTwo} \\ % FALSE
\foo{ArgTwo} \\ % TRUE
\foo{ArgOne} \\ % FALSE
\foo{ArgTwo} \\ % FALSE

\end{document}

Thanks, I just had a short look at the xstring documentation, it looks interesting, but I don't see how it could help here. My problem is not the comparison itself, because that works with "static values". I don't know how to compare to the saved-before value. Replacing "comparetothis" with "ArgOne" works, but I don't know how to put the value of \myoldvalue in there (or later at the place of @tempb). — user2567875, Jun 30 '15 at 09:00

egreg · Accepted Answer · 2018-07-23T10:09:17.877

I guess you want to use \pdf@strcmp:

\documentclass{article}
\usepackage{pdftexcmds}

\def\myoldvalue{emptystart} % initialize

\makeatletter
\newcommand\foo[1]{%
 \texttt{\string\myoldvalue}: \myoldvalue\\
 ARG1: #1\\
 \ifnum\pdf@strcmp{\myoldvalue}{#1}=\z@
   TRUE%
 \else
   FALSE%
 \fi
 \par
 \gdef\myoldvalue{#1}%
}
\makeatother

\begin{document}

\foo{ArgOne} % excepted print out is: FALSE
\foo{ArgOne} % TRUE
\foo{ArgTwo} % FALSE
\foo{ArgTwo} % TRUE
\foo{ArgOne} % FALSE
\foo{ArgTwo} % FALSE

\end{document}

enter image description here

An expl3 version:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\str_new:N \g_egreg_laststring_str
\str_gset:Nn \g_egreg_laststring_str { emptystart } % initial value

\NewDocumentCommand{\foo}{m}
 {
  The~current~value~is:~\texttt{\tl_use:N \g_egreg_laststring_str} \par
  ARG:~#1\par
  \str_if_eq:VnTF \g_egreg_laststring_str { #1 } { TRUE } { FALSE }
  \str_gset:Nn \g_egreg_laststring_str { #1 }
 }
\ExplSyntaxOff

\begin{document}

\foo{ArgOne} % excepted print out is: FALSE
\foo{ArgOne} % TRUE
\foo{ArgTwo} % FALSE
\foo{ArgTwo} % TRUE
\foo{ArgOne} % FALSE
\foo{ArgTwo} % FALSE

\end{document}

Compare Variables

1 Answers1