On Thu, 21 Feb 2002 01:11:01 +1100
"Sisyphus" <[EMAIL PROTECTED]> wrote:
> Hi,
>
> Ok - so I'm running the code below and it's working as I want - unless
> either of the 2 values being written to the file is 10. (ie unless $num = 8
> or 10).
>
> If the value is 10, then I get a couple of warnings about 'use of
> uninitialised value'.
> '10' is the only value I've found that exhibits this disgraceful behaviour.
>
> Ummmm ...... I'm a little hard pressed to make sense of that ........
> something to do with the newline characters or the chomping perhaps ?
>
> use warnings;
> my $file = "try";
> my $num = 111111112;
> open (WRITEB, ">$file")
> or die "Can't open WRITEB: $!";
> binmode WRITEB;
> print WRITEB pack("I",$num,), "\n";
if $num==10 you are really printing "\n\0\0\0\n" to the file on a little
endian machine like a PC. pack( "I", 10 ) gives "\n\0\0\0". The least
significant byte is 10 which is the ASCII newline character.
> print WRITEB pack("I",$num + 2), "\n";
> close (WRITEB)
> or die "Can't close WRITEB: $!";
>
> open (READ, "$file")
> or die "Can't open READ: $!";
> binmode READ;
> while (<READ>) {
Here you want to read one line at a time. If $num was 10 you will get 2
lines. The first one will be "\n" the 2nd "\0\0\0\n".
> chomp;
chomp makes "" from "\n".
> $ret = unpack("I", $_);
unpack( "I", "" ) yields undef.
> print $ret, "\n";
and here you get your warning
> }
> close (READ)
> or die "Can't close READ: $!";
>
In generally do not mix binary and line oriented IO. In your example you
can
print WRITEB pack("I",$num,);
without the newline and then use read or sysread:
read READ, $_, length( pack( "I", 0 ) );
> Cheers,
> Rob
>
>
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