conditionalsstrings
How do I do a conditional 'if then else' statement, based on length of string being greater than (or less than, or equal) a specified value.
For example, something Like
\def\mystring{XYZ}
\def\mythresh{1}
\ifthenelse{\stringlength{\mystring} > \mythresh}{TRUE}{FALSE}
where \stringlength is 'pseudo' for the relevant command, which I am unsure which is the most widely used.
Does the logical greater than operator apply here, or is there another command?
You don't need a package:
\ifnum\markscore>89
statement 1
\else
\ifnum\markscore>79
statement 2
\else
statement 3
\fi
\fi
update: the mandatory xinttools approach has been added
There are two problems. The first one is that \isin from package xifthen does
not expand its second argument, here \dbline. The second problem is that \isin
uses the LaTeX kernel \in@ which can not handle a \par token; but TeX will
always append a \par token at the end of file input via \read, except
if \endlinechar is set to -1.
The first problem can be handled by defining a wrapper \isinxp which expands its
second argument. The second problem (assuming \endlinechar is not -1) by testing
the end of file after having read the line and before the test.
\documentclass[12pt, a4paper]{article}
\usepackage{filecontents}
\begin{filecontents*}{cities.txt}
A;London
B;Berlin
C;Paris
\end{filecontents*}
\usepackage{xstring}
\usepackage{xifthen}
% star form as anyhow \isin is declared short, and furthermore
% uses internally \in@ from the LaTeX kernel which is short
\newcommand*{\isinxp}[2]{\expandafter\isinxpp\expandafter{#2}{#1}}
\newcommand*{\isinxpp}[2]{\isin {#2}{#1}}
\begin{document}\thispagestyle{empty}
\newread\dbcities
\openin\dbcities=cities.txt
We start here:
\loop
\read\dbcities to \dbline
% (testing) \texttt{\meaning\dbline}
\unless\ifeof\dbcities
\ifthenelse{\isinxp{A}{\dbline}}
{\StrCut{\dbline}{;}{\colA}{\colB}
\colA: \colB \\}
{}
\repeat
\closein\dbcities
\end{document}
The mandatory xinttools approach:
(I have corrected the key matching, as it stood a search for BB would have returned a false positive for a data line with B as key. Notice that the fact that a data line containing BB as key returns positive when looking for B is the expected thing, as the OP used \isin.)
\documentclass[12pt, a4paper]{article}
\usepackage{filecontents}
\begin{filecontents*}{\jobname.dat}
A;London
B; Berlin
BB; Hamburg
C ; Paris
A ; London again
D;Roma
\end{filecontents*}
\usepackage{xinttools}
\newread\datastream
% to issue warnings if command names already in use, then one knows one
% has to change them (depens on loaded packages)
\newcommand {\onedataline}{}
\newcommand {\printdatakey}{}
\newcommand {\printdatatestkey}{}
\newcommand {\printdataprocessline}{}
\newcommand {\printdata}[2]{% #1 = file name, #2 string to test
\openin\datastream=#1\relax
% the string key will be trimmed of its leading and trailing spaces
\edef\printdatakey
{\expandafter\xintZapSpaces\expandafter{\detokenize{#2}}}%
%
\edef\printdatatestkey
{\unexpanded{\def\printdatatestkey ##1}\printdatakey
\unexpanded{##2\relax ##3\par {\ifx\relax##2\relax\else ##3\par\fi}}}
%
\printdatatestkey % sets up \printdatatestkey macro to seek the key.
% [added a ; to avoid false positives if for example the seeked key is BB
% and the actual one is B.]
\edef\printdataprocessline ##1;##2\relax
{\noexpand\printdatatestkey ##1;\printdatakey\relax
\printdatakey: \noexpand\xintZapSpaces {##2}\noexpand\par }%
%
\xintloop
\read\datastream to \onedataline
% detokenize the line for safe handling.
% \odef expands once the argument, this is enough
\odef\onedataline{\detokenize\expandafter{\onedataline}}%
\unless\ifeof\datastream
\expandafter\printdataprocessline\onedataline\relax
% j'aurais dû faire directement
% \expandafter\printdataprocessline\detokenize\expandafter{\onedataline}\relax
\repeat
\closein\datastream
}
\begin{document}\thispagestyle{empty}
Testing A:
\printdata{\jobname.dat}{ A }
\medskip
Testing B:
\printdata{\jobname.dat}{ B}
\medskip
% sans le ; faux positif sur Berlin
Testing BB:
\printdata{\jobname.dat}{BB}
\medskip
Testing D:
\printdata{\jobname.dat}{ D }
\end{document}
Best Answer
Use the
xstringpackage:\StrLen{<stuff>}[<name>]stores the length of<stuff>in the control sequence<name>.The use of
xifthenis not really necessary. See How to form “if … or … then” conditionals in TeX? and the related Why is theifthenpackage obsolete? for alternatives.stringstringsprovides similar functionality: