Graphics, Figures & Tables ⇒ Image can't be included with twice \newcommand expansion

[EmilioLazo]

Hi.

In the following code:

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Code, edit and compile here:

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\documentclass{article}
\newcommand{\test}{example-grid-100x100bp.jpg}
\newcommand{\testx}{\test}
\let\testxx\test
\usepackage{graphicx}
\begin{document}
test \includegraphics{\test} 
testx \includegraphics{\testx}
testxx \includegraphics{\testxx}
\end{document}
 
 
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Run LaTeX here

Both first and third image appears but second one doesn't:

! LaTeX Error: File `example-grid-100x100bp.jpg' not found.

If '.jpg' extension is removed from \test command definition, all three images appears.

Why?

[localghost]

Then just drop the suffix. In the most cases it is superfluous anyway.


Thorsten

[EmilioLazo]

But what is happening anyway?

Why the difference in the behaviour between first/third image inclusion and second?

(pdf)latex says that it can't find 'example-grid-100x100bp.jpg', the same file of the other two cases.

[cgnieder]

But what is happening anyway?

The error message is actually misleading. When you do

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Code, edit and compile here:

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\def\test{picture.jpg}
\def\testx{\test}
...
\includegraphics{\testx}
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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Run LaTeX here

the error message means to say »File `\test' not found«. The actual inclusion is done by the command \Ginclude@graphics which calls

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\filename@parse{#1}
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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The \filename@parse macro contains the code

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\expandafter\filename@path#1/\\
 
 
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which means that the argument of \includegraphics is expanded once. This is why the first test succeeds. In the second case it finds the file »\test«.

The above mentioned \filename@parse now calls \filename@path which in this case finds no directory specified and thus assumes the current path and calls \filename@simple#1.\\ which checks for an extension. It finds none and lets \filename@ext to \relax. It also defines \edef\filename@base{#1}. This is an \edef which means it's contents get fully expanded. That means that \filename@base is now picture.jpg.

These macros now are checked by \Ginclude@graphics. If \filename@ext is equal to \relax it looks for a match of \filename@base plus one of the allowed extensions. This would be picture.jpg.png, for example. Such a file does not exist so you get the error message. Without an extension this doesn't matter since \filename@base would be picture and it would find picture.jpg.

Regards