Bdtyktl

I have some code for formatting names. However, the ifempty macro from xifthen is unable to detect empty/null output from xstring macros such as StrBetween. The same goes for the equal {} method. How can I detect empty output from StrBetween? The below code for some reason compiles and does not work.

documentclass{article}



usepackage{xstring}

usepackage{xifthen}



newcommand{name}{John Doe}



newcommand{middleinitial}{%

    StrBetween{name}{ }{.}

}



newcommand{test}{%

    ifthenelse{isempty{middleinitial}}%

        {Whoo hoo!}%

        {Not whoo hoo.}

}



begin{document}



test



end{document}

Any ideas?

middleinitial is not expandable, and therefore you cannot properly test whether there is a middle initial in name or not. You'll have to store the output (the middle initial) first using the optional argument at the end of StrBetween{<str>}{<from>}{<to>}[<macro>] and then you can check for an empty argument:

documentclass{article}



usepackage{xstring}



newcommand{name}{John Doe}



makeatletter

newcommand{middleinitial}{%

  StrBetween{name}{ }{.}[@middleinitial]%

}



newcommand{test}{%

  middleinitial% Find middle initial

  % https://tex.stackexchange.com/q/53068/5764

  expandafterifexpandafterrelaxexpandafterdetokenizeexpandafter{@middleinitial}relax

    Whoo hoo!% No middle initial

  else

    Not whoo hoo.% A middle initial

  fi

}

makeatother



begin{document}



test % Whoo hoo.



renewcommand{name}{John F. Doe}%

test % Not whoo hoo!



end{document}

Werner already explained, why middleinitial isn't expandable due to the usage of xstring macros.

I present a shorter way in order to test for the emptiness of middleinitial by using ifblank from etoolbox package. There are still two expandafter statements required, but not a bunch of 5 of them. In addition, I find etoolbox much more convenient than ifthen or xifthen.

expandafterifblankexpandafter{middleinitial}{true branch}{false branch} is necessary, because ifblank does not expand its first argument, i.e. without expandafter the macro 'sees' middleinitial, but not what the content which is stored in that macro. It must be expanded first before ifblank performs the test.

The expandafter primitive looks ahead of ifblank, i.e. it ignores ifblank first and detects the { of the first argument. Unfortunately, this is not what is desired (and not expandable anyway), so we must jump over { again, i.e.

expandafterifblankexpandafter{middleinitial}{...}{...}

will allow TeX/LaTeX to 'jump' over ifblank to the second expandafter, that jumps over { to middleinitial and expands that sequence -- after this is done, TeX continues with ifblank{expanded version of middleinitial}{...}{...} and performs the test finally.

documentclass{article}



usepackage{xstring}

usepackage{etoolbox}



newcommand{name}{John C.  Doe}



newcommand{othername}{John Doe}





newcommand{testinitial}[3]{%

  begingroup

  StrBetween{#1}{ }{.}[middleinitial]%

  expandafterifblankexpandafter{middleinitial}{#2}{#3}%

  endgroup

}





begin{document}







testinitial{name}{Whoo hoo!}{Not whoo hoo.}



testinitial{othername}{Whoo hoo!}{Not whoo hoo.}



end{document}