LaTeX Optional Arguments

Question

How do you create a command with optional arguments in LaTeX  Something like    newcommand  sec  2          section   1          ifsecondargument             and  2          fi            Then  I can call it like   sec Hello   Output  Hello  sec Hello  Hi   Output  Hello and Hi

User · Accepted Answer

Example from the guide    newcommand  example  2  YYY  Mandatory arg   2                                   Optional arg   1    This defines  example to be a command with two arguments   referred to as  1 and  2 in the   lt definition gt  --nothing new so far   But by adding a second optional argument to this  newcommand   the  YYY   the first argument   1  of the newly defined  command  example is made optional with its default value being YYY   Thus the usage of  example is either       example BBB  which prints  Mandatory arg  BBB  Optional arg  YYY  or      example XXX  AAA  which prints  Mandatory arg  AAA  Optional arg  XXX

User · Answer

All you need is the following    makeatletter  def sec 1  def tempa  1  futurelet next sec i   Save first argument  def sec i  ifx next bgroup expandafter sec ii else expandafter sec end fi  Check brace  def sec ii 1  section   tempa  and  1   Two args  def sec end  section   tempa   Single args  makeatother   sec Hello   Output  Hello  sec Hello  Hi   Output  Hello and Hi

User · Answer

All of the above show hard it can be to make a nice  flexible  or forbid an overloaded  function in LaTeX      that TeX code looks like greek to me   well  just to add my recent  albeit not as flexible  development  here s what I ve recently used in my thesis doc  with   usepackage ifthen     provides conditonals      Start the command  with the  optional  command set blank by default    newcommand   figHoriz   4          I then have the macro set a temporary variable   temp    differently depending on whether or not the optional argument is blank   This could be extended to any passed argument    ifthenelse    equal   1         if short caption not specified  use long caption  no slant         def temp   caption  4   textsl  4          if  1    blank        def temp   caption  1   textsl  4          else  not blank    Then I run the macro using the  temp   variable for the two cases    Here it just sets the short-caption to equal the long caption if it wasn t specified by the user     begin figure          begin center           includegraphics width 350 pt   3           temp    see above for caption etc           label  2       end center   end figure      In this case I only check for the single   optional  argument that  newcommand   provides   If you were to set it up for  say  3  optional  args  you d still have to send the 3 blank args     eg    MyCommand  first arg             which is pretty silly  I know  but that s about as far as I m going to go with LaTeX - it s just not that sensical once I start looking at TeX code     I do like Mr  Robertson s xparse method though  perhaps I ll try it

User · Answer

The general idea behind creating  optional arguments  is to first define an intermediate command that scans ahead to detect what characters are coming up next in the token stream and then inserts the relevant macros to process the argument s  coming up as appropriate  This can be quite tedious  although not difficult  using generic TeX programming  LaTeX s   ifnextchar is quite useful for such things   The best answer for your question is to use the new xparse package  It is part of the LaTeX3 programming suite and contains extensive features for defining commands with quite arbitrary optional arguments   In your example you have a  sec macro that either takes one or two braced arguments  This would be implemented using xparse with the following     documentclass article   usepackage xparse   begin document   DeclareDocumentCommand sec  m g           1           IfNoValueF   2    and  2              sec Hello     sec Hello  Hi    end document    The argument   m g   defines the arguments of  sec  m means  mandatory argument  and g is  optional braced argument    IfNoValue T  F  can then be used to check whether the second argument was indeed present or not  See the documentation for the other types of optional arguments that are allowed

User · Answer

I had a similar problem  when I wanted to create a command   dx  to abbreviate    mathrm d x  i e  put an extra space before the differential of the integral and have the  d  upright as well   But then I also wanted to make it flexible enough to include the variable of integration as an optional argument  I put the following code in the preamble    usepackage ifthen    newcommand  dx  1          ifthenelse   equal  1              ensuremath    mathrm d x           ensuremath    mathrm d  1       Then    begin document        int x dx         int t dx t     end document    gives  dx with optional argument

User · Answer

Here s my attempt  it doesn t follow your specs exactly though  Not fully tested  so be cautious    newcount seccount   def sec        seccount0       let go secnext go     def secnext 1        def last  1        futurelet next secparse     def secparse        ifx next bgroup          let go secparseii      else          let go seclast      fi      go     def secparseii 1        ifnum seccount 0   fi      advance seccount1 relax      last      def last  1        futurelet next secparse     def seclast  ifnum seccount 0   and  fi last     sec a  b  c  d  e    outputs  a  b  c  d and e    sec a    outputs  a    sec a  b    outputs  a and b

[latex] LaTeX Optional Arguments

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