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