catch command

[Michael Hertel]

What am I doing wrong?

I’m under the impression that err is valued only if something blows up.

catch {something blew up} err

What I’m trying to do is look for a bad or missing date so I thought that:

set txa4 {}

set err {}

catch {set data [clock scan $txa4]} err

err would be valued only if the date was missing or invalid and the scan command would blow up. But when I check $err, it seems to be valued with something.

Topic

[Rob Abbott]

Hi Mike

catch will return 1 if error, 0 if no error

err will be set to either the error or the return value of the statements inside braces.

It’s best to avoid using “set” inside a catch.  I would revise your code like this

if [catch {clock scan $txa4} data] {

  # an error occurred – data contains the error

} else {

  # no error occurred – data contains the result of clock scan

}

Rob Abbott
Cloverleaf Emeritus

[Michael Hertel]

Thanks Rob!

[Author]

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