Empty parameter in xdef definition

Question

Considering this definition of a latex macro:

\newcommand\createCMDMANUV[4]{%
  \expandafter\@ifdefinable\csname #3#2\endcsname{%
    \expandafter\xdef\csname #3#2\endcsname##1{%
      \noexpand\vcenteredhbox{%
      \noexpand\includegraphics[width=##1,trim=0 0 1 -1]{BD_CATIA/#4/#1.png}}%
    }%
  }%
}

I try to deal with empty (not optional) parameter. So I tried this definition but it is not working:

\newcommand\createCMDMANUV[4]{%
  \expandafter\@ifdefinable\csname #3#2\endcsname{%
    \expandafter\xdef\csname #3#2\endcsname##1{%
      \noexpand\vcenteredhbox{%
      \ifdefempty{##1}{\def\widthCATIA{3cm}}{\def\widthCATIA{##1}}%
      \includegraphics[width=\widthCATIA,trim=0 0 1 -1]{BD_CATIA/#4/#1.png}}%
    }%
  }%
}

I think it is due to the fact that \widthCATIA is not well defined but what is the right syntax...

I call the command \createCMDMANUV{\tA}{\tB}{\tC}{\tD} where \tA to \tD contains string.

For example if \tC contains AVV and \tB contains test the macro build the command \AVVtest.

MWE (base on the same idea):

\documentclass{standalone}
\RequirePackage{xstring}
\RequirePackage{etoolbox}

\makeatletter
\newcommand\createCMDMANUV[2]{%
  \expandafter\@ifdefinable\csname #1#2\endcsname{%
    \expandafter\xdef\csname #1#2\endcsname##1{%    
      \noexpand\textbf{##1}%
    }%
  }%
}
\makeatother

\begin{document}
\def\tA {AA}
\def\tB {BB}    
\createCMDMANUV{\tA}{\tB}

\AABB{coucou}   
\end{document}

MNWE (Minimal Not Working Example :-) ):

\documentclass{standalone}
\RequirePackage{xstring}
\RequirePackage{etoolbox}

\makeatletter
\newcommand\createCMDMANUV[2]{%
  \expandafter\@ifdefinable\csname #1#2\endcsname{%
    \expandafter\xdef\csname #1#2\endcsname##1{%    
    \ifcsempty{##1}{ \expandafter\xdef\csname ttMANU\endcsname{Ahah}}{ \expandafter\xdef\csname ttMANU\endcsname{ohoh}}%
      \noexpand\textbf{\csname ttMANU\endcsname}%
    }%
  }%
}
\makeatother

\begin{document}
\def\tA {AA}
\def\tB {BB}    
\createCMDMANUV{\tA}{\tB}

\AABB{}    
\AABB{aa}
\end{document}

\ifcsempty seems not doing well the empty test.

SOLUTION of my MNWE:

\documentclass{standalone}
\RequirePackage{xstring}
\RequirePackage{etoolbox}

\makeatletter
\newcommand\createCMDMANUV[2]{%
\ifdefempty{##1}{\def\ttMANU{ahah}}{\def\ttMANU{ohoh}}%
  \expandafter\@ifdefinable\csname #1#2\endcsname{%
    \expandafter\xdef\csname #1#2\endcsname##1{%    
    \noexpand\ifblank{##1}{\def\noexpand\ttMANU{ahah}}{\def\noexpand\ttMANU{##1}}%%
      \noexpand\textbf{\noexpand\ttMANU}%
    }%
  }%
}
\makeatother

\begin{document}    
\def\tA {AA}
\def\tB {BB}    
\createCMDMANUV{\tA}{\tB}

\AABB{}    
\AABB{aa}      
\end{document}

Answer 1

You are trying to expand \ifdefempty at definition time; but you should use \ifblank;

\newcommand\createCMDMANUV[4]{%
  \expandafter\@ifdefinable\csname #3#2\endcsname{%
    \expandafter\xdef\csname #3#2\endcsname##1{%
      \noexpand\vcenteredhbox{%
      \noexpand\ifblank{##1}{\def\noexpand\widthCATIA{3cm}}{\def\noexpand\widthCATIA{##1}}%
      \noexpand\includegraphics[width=\noexpand\widthCATIA,trim=0 0 1 -1]{BD_CATIA/#4/#1.png}}%
    }%
  }%
}

If I call

\def\tA{AA}\def\tB{test}\def\tC{AVV}\def\tD{DD}

\createCMDMANUV{\tA}{\tB}{\tC}{\tD}

\show\AVVtest

I get the following response:

> \AVVtest=macro:
#1->\vcenteredhbox {\ifblank {#1}{\def \widthCATIA {3cm}}{\def \widthCATIA {#1}
}\includegraphics [width=\widthCATIA ,trim=0 0 1 -1]{BD_CATIA/DD/AA.png}}.

---

It's easier with expl3:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand\createCMDMANUV { mmmm }
 {
  \guuk_create_cmd_manuv:xxxx { #1 } { #2 } { #3 } { #4 }
 }

\tl_new:N \l__guuk_width_catia_tl

\cs_new_protected:Nn \guuk_create_cmd_manuv:nnnn
 {
  \cs_new_protected:cpn { #3#2 } ##1
   {
    \vcenteredhbox
     {
      \tl_if_empty:nTF { ##1 }
       { \tl_set:Nn \l__guuk_width_catia_tl { 3cm } }
       { \tl_set:Nn \l__guuk_width_catia_tl { ##1 } }
      \includegraphics[width=\l__guuk_width_catia_tl,trim=0 ~ 0 ~ 1 ~ -1]{BD_CATIA/#4/#1.png}
     }
   }
 }

\cs_generate_variant:Nn \guuk_create_cmd_manuv:nnnn { xxxx }
\ExplSyntaxOff
\def\tA{AA}\def\tB{test}\def\tC{AVV}\def\tD{DD}

\createCMDMANUV{\tA}{\tB}{\tC}{\tD}

\show\AVVtest

The response is

> \AVVtest=\protected\long macro:
#1->\vcenteredhbox {\tl_if_empty:nTF {#1}{\tl_set:Nn \l__guuk_width_catia_tl {3
cm}}{\tl_set:Nn \l__guuk_width_catia_tl {#1}}\includegraphics [width=\l__guuk_w
idth_catia_tl ,trim=0 0 1 -1]{BD_CATIA/DD/AA.png}}.

How it works

1. I define a “user level command” \createCMDMANUV with four arguments. Its task is just to pass the arguments to \guuk_create_cmd_manuv:xxxx

2. I define the \guuk_create_cmd_manuv:nnnn function; the four n mean that it is a macro with four “normal” arguments.

3. This function in turn defines a new macro based on the passed arguments; it does \cs_new_protected:cpn which is the analog of \expandafter\def\csname ...\endcsname, but adding the “undefinedness test”, so

   \cs_new_protected:cpn { <tokens> } #1 { ... }
   

   is what you're doing with

   \expandafter\def\csname <tokens>\endcsname##1{...}
   

4. As requested, the constructed macro has one argument, which is tested for emptyness with \tl_if_blank:nTF that returns the second argument if the argument is blank, the third argument otherwise. This test is the same as etoolbox \ifblank; the code just sets the internal token list to the argument, if not blank or to 3cm

5. The inner code of the built function is exactly the same as you build with the traditional method, but without any \noexpand

6. The final trick: with

   \cs_generate_variant:Nn \guuk_create_cmd_manuv:nnnn { xxxx }
   

   we define from the stated function another one named \guuk_create_cmd_manuv:xxxx that, when called, first does full expansion of its four arguments and then passes the expanded arguments as normal arguments to \guuk_create_cmd_manuv:nnnn

7. Note that in the programming environment, between \ExplSyntaxOn and \ExplSyntaxOff, spaces and blank lines are ignored, so there's no need of worrying about protecting end-of-lines. The only small complication is that wanted spaces must be explicitly inserted with ~ as in the value to the trim key above.

Answer 2

I removed my first answer because it seems that your code is overcomplicated (as usually for many users:). First of all, you have to ask why I need to use \xdef instead normal \gdef? I don't see the reason. So, your example can work with \gdef:

\def\createCMDMANUV#1#2#3#4{%
  \expandafter\@ifdefinable\csname #3#2\endcsname{%
    \expandafter\gdef\csname #3#2\endcsname##1{%
      \vcenteredhbox{%
      \includegraphics[width=\widthCATIA{##1},trim=0 0 1 -1]{BD_CATIA/#4/#1.png}}%
    }%
  }%
}
\def\withCATIA#1{\ifx^#1^3cm\else#1\fi}

Edit (in response to the comment about expansions of parameters during declaration). If you need to use expanded parameters in your \declaremacro code, then you can think about the following code:

\def\delcleremacro#1#2#3#4{\edef\tmp{\noexpand\declaremacroA{#1}{#2}{#3}{#4}\tmp}
\def\declaremacroA#1#2#3#4{%
    \expandafter\gdef\csname #3#2\endcsname##1{%
        ... here is my complicated macro, which uses declared
            and {\bf expanded} parameters #1, #2, #3, #4 and one real parameter ##1.
            I need not to use fifty times \noexpand here.
            The test of empty parameter ##1 can be done by
            \ifx^##1^empty\else nonempty\fi or (more robust but nonexpandable)
            \def\tmp{##1}\ifx\tmp\empty \def\tmp{3cm}\else\def\tmp{##1}\fi
            and you can use \tmp in your meaning of \widthCATIA.
            Here is no \noexpand problem.
}}