411 REFERENCE · Wikibooks
TeX/ifx
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
Synopsis
\ifx \Macro1 \Macro2
<tex commands>
\else
<tex commands>
\fi
Description
With the \ifx command you can perform conditional compilation by testing for macro equivalence.
It does not expand the given macros. The two macros are considered equal if
both are macros and
the first level expansion is equal and
they have the same state with regards to \long and \outer
See also the command \def.
Examples
For example, let's say we define a new macro just to do conditional compilation:
\def \myMacro {}
Then we can use \ifx to check if this macro is defined or not.
\ifx \myMacro \undefined
This will be processed if myMacro is not defined.
\else
This will be processed if myMacro is defined.
\fi
See also on the use of this method for testing whether
a macro is defined.