how to throw a warning in latex?

Question

I want to know how to throw a warning when latex reach to a certain point.

For instance:

\switch [\exp1]
\case{{case 0}}
        %do whatever
\case{{case 1}}
        %do whatever
\otherwise
        %throw warning
\endswitch

Is it possible to do it?

Are the cases referring to numbers? Or could this be general text? — Werner, Oct 19 '16 at 17:19
it can be whatever, my main concern is how to throw the warning given you get to some point (in the example, would be the otherwise) — Pablo Guerrero, Oct 19 '16 at 17:26
Related/duplicate: How do I generate a warning for an undefined control sequence — Werner, Oct 19 '16 at 17:28
You are right! I was not able to find that question when I searched :(. However, I think @Heiko Oberdiek's answer to this one is more complete than the ones there! :) — Pablo Guerrero, Oct 19 '16 at 19:05
Somewhat special case of macros - Is there any way to generate custom errors/warnings in LaTeX? - TeX - LaTeX Stack Exchange — user202729, Jul 27 '22 at 18:03

Heiko Oberdiek · Accepted Answer · 2022-08-02T17:31:08.997

LaTeX provides warnings, which are printed to the console/.log file, both with including the current line number and without.

A class has:

\ClassWarning{<class name>}{<message>}
\ClassWarningNoLine{<class name>}{<message>}

A package has:

\PackageWarning{<package name>}{<message>}
\PackageWarningNoLine{<package name>}{<message>}

LaTeX uses:

\@latex@warning{<message>}
\@latex@warning@no@line{<message>}

The documentation can be found in "LaTeX2e for class and package writers" (texdoc clsguide).

score 2 · Answer 2 · answered Aug 02 '22 at 20:23

TeX (in all formats) provides messages, which are printed to the console/.log file.

\wlog{text}   % prints expanded text to log only, CR added

You can define \def\wterm{\immediate \write16 } and then:

\wterm{text}  % prints expanded text to terminal and to the log, CR added

There is \message primitive:

 \message{text} % prints expanded text to terminal and to the log, no CR added

Note that \the\inputlineno expands to the current line number of the input file.

2 Answers2