catching exceptions - Tcl style

Other Facilities in Tcl example from a Well House Consultants training course
More on Other Facilities in Tcl [link]

This example is described in the following article(s):
• Exceptions - Tcl style - [link]

Source code: goalie Module: T214

# catching exceptions - Tcl style

# The unknown command is run if you call a command which does not exist!

proc unknown {args} {
        puts "lost:-- $args"
        }

# Set up some values for the demo

set val default
set debug 0

puts "How long? "
gets stdin len

puts "How wide? "
gets stdin wide

# variables len and wide MAY contain values that work in expr, or they may
# contain errors!

# catch will trap the error.

# - the message is put into a separate variabe that you MAY use rather than
# being sent to stderr

# - catch returns a true or false status to let you know whether or not there
# was and error

if {! [catch {
        set val [expr $len * $wide]
        } errmsg ]} {
   puts "Yes, that worked nicely"
} else {
   puts "Someone's done an oopsie"
   if $debug {puts "message is $errmsg"}
}

# An undefined command - that would normally crash a Tcl program

porridge milk salt sultanas marmite

puts "area is $val"

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* Learning to program in Tcl
* Tcl Programming
* Tcl Programming
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