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Undefined values: Difference between revisions
→Tcl: Added implementation
m (Correct omit from use) |
(→Tcl: Added implementation) |
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=={{header|Perl}}==
<lang perl>#!/usr/bin/perl -w
use strict;
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=={{header|PHP}}==
<lang php><?php
// Check to see whether it is defined
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=={{header|Python}}==
<lang python># Check to see whether it is defined▼
▲# Check to see whether it is defined
try: var
except NameError: print "var is undefined at first check"
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# Because most of the output is conditional, this serves as
# a clear indicator that the program has run to completion.
print "Done"</lang>
</lang>▼
Results in:
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=={{header|Ruby}}==
<lang ruby># Check to see whether it is defined▼
▲# Check to see whether it is defined
puts "var is undefined at first check" unless defined? var
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# Because most of the output is conditional, this serves as
# a clear indicator that the program has run to completion.
puts "Done"</lang>
Results in:
<pre>var is undefined at first check
Done
=={{header|Tcl}}==
Tcl does not have undefined ''values'', but ''variables'' may be undefined by being not set.
<lang tcl># Variables are undefined by default and do not need explicit declaration
# Check to see whether it is defined
if {![info exists var]} {puts "var is undefind at first check"}
# Give it a value
set var "Screwy Squirrel"
# Check to see whether it is defined
if {![info exists var]} {puts "var is undefind at second check"}
# Remove its value
unset var
# Check to see whether it is defined
if {![info exists var]} {puts "var is undefind at third check"}
# Give it a value again
set var 12345
# Check to see whether it is defined
if {![info exists var]} {puts "var is undefind at fourth check"}
puts "Done"</lang>
Yields this output:
<pre>
var is undefind at first check
var is undefind at third check
Done
</pre>
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