Text Formatting ⇒ ifx and ifthenelse

[heavytull]

Can anyone explain the syntax of:

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ifx&#1&%
         \else{something\fi}
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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?
and what is the difference with:

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\ifthenelse{\equal{#1}{}}{}{something}
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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?

[cgnieder]

\ifx tests if the two following tokens are equal:

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Code, edit and compile here:

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\ifx<1><2>
 true
\else
 false
\fi
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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Depending on that either »true« or »false« is executed.

In your example

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Code, edit and compile here:

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\ifx&#1&
 true
\else
 false
\fi
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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it is used to detect whether the argument #1 is empty or not. An empty #1 would mean that \ifx sees two »&« directly after one another which would lead to »true«.

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Code, edit and compile here:

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\documentclass{article}
\begin{document}
\newcommand\test[1]{%
 \ifx&#1&%
  true%
 \else
  false%
 \fi}
\test{} % true
blank is \emph{not} empty:
\test{ } % false
\test{a} % false
\end{document}
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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Run LaTeX here

The second code does the same:

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Code, edit and compile here:

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\documentclass{article}
\usepackage{ifthen}
\begin{document}
\newcommand\test[1]{%
  \ifthenelse{\equal{#1}{}}{true}{false}}
\test{} % true
\test{ } % false
\test{a} % false
\end{document}
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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In many cases it won't matter which version you use but I suspect that the second one is mor robust in some cases. Since I haven't checked how \ifthenelse is defined I might be mistaken, though.