uninitialized variable

Fingo has asked for the wisdom of the Perl Monks concerning the following question:

This is a subroutine from a program of mine and it's call. Why does -w give me an uninitialized value error, I defined it correctly. The program works right if I turn off -w.

#!/usr/bin/perl 
print CalcBalance(\"balance.log");
sub CalcBalance {
    my ($balance, @log);
    my $location = 0;  #because my $location = shift(@ARGV) does not w
+ok either.
    $location = shift(@ARGV);
# the following is not needed
#    open (RBALANCE, $location);
#    @log = <RBALANCE>;
#    $balance = $log[-1];
#    close (RBALANCE);
#    if (@ARGV && $ARGV[0] != 0) {     # we check to see if there is a
+nother 
#                                  # argument (the amount to change) a
+nd 
#                                  # it is not 0.
#    
#    my $toChange = shift (@ARGV); # we only declare this if another 
#                                  # argument exists to make the test 
#                                  # above work. 
#    $balance += $toChange;
#    open (WBALANCE, ">>$location");
#    print WBALANCE $balance;
#    close (WBALANCE);
#    }
}
[download]

Thanks

Comment on uninitialized variable Download Code

Replies are listed 'Best First'.
Re: uninitialized variable by bbfu (Curate) on Feb 28, 2001 at 04:01 UTC
In a subroutine, you need to use `@_` not `@ARGV`. `@ARGV` is only for parameters passed into the script when invoking it (ie, from the command-line). `@_` is where subroutine parameters are passed. So change all the lines that say `shift(@ARGV)` to `shift(@_)` and it should be fine. bbfu Seasons don't fear The Reaper. Nor do the wind, the sun, and the rain. We can be like they are.	[reply] [d/l] [select]
Re: uninitialized variable by arturo (Vicar) on Feb 28, 2001 at 04:04 UTC
`$location = shift(@ARGV);` will set `$location` to `undef` if no arguments have been passed to the script (`@ARGV` refers only to the command line, as bbfu points out). That's why you're getting the warning. For cases like these, you can either do: `my $location = shift @ARGV or die "usage: $0 [filename]\n";` [download] or, if you want a default, `my $location = shift \|\| 'default value';` [download] Minor amplification `shift` called without an explicit argument will return the next element of `@ARGV` if it is called outside a subroutine, and returns the next element of `@_` if called within a subroutine. HTH Philosophy can be made out of anything. Or less -- Jerry A. Fodor	[reply] [d/l] [select]


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