trying to return a hash from a perl function and getting "can't use string ("0") as a HASH ref...." - perl

Question

I have a Perl function (named readDicomFile) which ends thusly:
return { 'fileProperties' => \%fileProperties, 'filehandle' => *FH, 'buffersize' => $buffersize };
the code that calls it looks like this:
$file = readDicomFile( $ARGV[0] );
#use Data::Dumper;
#print Dumper $file;
my #imageData;
local *FH = $file->{filehandle};
while ( read(FH, $_, $file->{buffersize}) ) {
push #imageData, unpack( 'S' x ( $file->{buffersize}/($file->{fileProperties}->{bitsAllocated}/8) ), $_ );
}
print "DEBUG: found ", (scalar #imageData), " elements\n";
I get this output:
Can't use string ("0") as a HASH ref while "strict refs" in use at ./test.pl line 17.
DEBUG: found 262156 elements
When I try to figure out what's happening with my data structure, I uncomment the two lines for using Data::Dumper and I get this:
$VAR1 = {
'fileProperties' => {
'echoNumber' => '',
'highBit' => 11,
'rows' => 512,
'bitsAllocated' => 16,
'modality' => 'CT',
'echoTime' => '',
'windowCenter' => '200',
'studyDescription' => 'CT SINUS / FACIAL WITH CONTRAST ',
'repetitionTime' => '',
'sequenceName' => '',
'method' => 'perl method',
'seriesNumber' => '502 ',
'imageNumber' => '0 ',
'windowWidth' => '50',
'trailer' => 0,
'pixelRepresentation' => 0,
'sliceLocation' => '',
'bitsStored' => 12,
'ultrasoundColorData' => '',
'rescaleIntercept' => 0,
'photometricInterpretation' => 'MONOCHROME2 ',
'description' => 'Patient Protocol',
'imageDataType' => '',
'imagePosition' => '',
'columns' => 512,
'studyDate' => '20140505'
},
'filehandle' => *Radiology::Images::FH,
'buffersize' => '1024'
};
I've played around with several different idioms for returning the hash values from the function (like passing back a hash or a hashref), but I'm always getting the same error.
Does anyone have insight into my problem?
Thanks in advance.
EDIT:
I've been playing around with this all afternoon. Here is the entirety of the current test.pl
#!/usr/bin/perl -w
use lib '/etc/perl';
use strict;
use Radiology::Images;
my $file = $ARGV[0];
$file = readDicomFile( $file );
print STDERR "DEBUG: $file->{fileProperties}->{bitsAllocated}\n";
my #imageData;
# while ( $readsize = read ( $file->{filehandle}, $_, $file->{buffersize} ) ) {
# push #imageData, unpack( 'S' x ( $file->{buffersize}/($file->{fileProperties}->{bitsAllocated}/8) ), $_ );
# }
my $readsize;
my $imagesize = $file->{fileProperties}->{columns} * $file->{fileProperties}->{rows};
print "DEBUG: should find $imagesize elements\n";
while ( $imagesize > 0 ) {
$readsize = read ( $file->{filehandle}, $_, $file->{buffersize} );
push #imageData, unpack( 'S' x ( $readsize/( $file->{fileProperties}->{bitsAllocated}/8 ) ), $_ );
$imagesize -= $readsize /( $file->{fileProperties}->{bitsAllocated}/8 );
}
print "DEBUG: found ", (scalar #imageData), " elements\n";
...which gives me this output
DEBUG: 16
DEBUG: should find 262144 elements
Can't use string ("0") as a HASH ref while "strict refs" in use at /root/test.pl line 7.
DEBUG: found 262144 elements
...HOWEVER, when I change the 'while' loop in line #15 to
while ( $imagesize > 34816 ) {
I get this output:
DEBUG: 16
DEBUG: should find 262144 elements
DEBUG: found 227328 elements
So, it would appear that something I'm doing in a loop between lines 15 and 18 causes an error that goes back in time to line 7. Thus, my problem has never been with passing the hash back from my function. ??
BTW, the number 34816 was arrived experimentally. 34816 doesn't trigger the error, 34815 does.
Given this is looking completely whacky and given that the code works the way I think it is supposed to despite the error, I guess I'll just assume it is a language bug and turn my attention to just suppressing the error message.
2nd EDIT:
This is test.pl now:
#!/usr/bin/perl -w
use lib '/etc/perl';
use strict;
use Radiology::Images;
my $file = $ARGV[0];
$file = readDicomFile( $file );
my #imageData;
my $readsize;
while ( $readsize = read ( $file->{filehandle}, $_, $file->{buffersize} ) ) {
push #imageData, unpack( 'S' x ( $readsize/($file->{fileProperties}->{bitsAllocated}/8) ), $_ );
}
print "DEBUG: found ", (scalar #imageData), " elements\n";
gives me this output:
Can't use string ("0") as a HASH ref while "strict refs" in use at /root/test.pl line 9.
DEBUG: found 5638203 elements
if I comment out the 'use strict' line, I get:
Use of uninitialized value in ref-to-glob cast at /root/test.pl line 9.
Use of uninitialized value in read at /root/test.pl line 9.
read() on unopened filehandle at /root/test.pl line 9.
DEBUG: found 5638215 elements
I, uh, obviously...don't understand this....

Answer 1

You need to return a reference to your file handle:
return {
'fileProperties' => \%fileProperties,
'filehandle' => \*FH, # <--- reference.
'buffersize' => $buffersize,
};
And then when reading, you can work directly on the filehandle, you don't have to transfer it to a fileglob:
# local *FH = $file->{filehandle}; <--- Not Needed. Below, just use the lexical fh
while ( read($file->{filehandle}, $_, $file->{buffersize}) ) {
If you work with lexical file handles from the very beginning, it becomes a lot more obvious how to pass them:
open my $fh, '<', 'myfile.txt' or die "Can't open: $!";
return {
'fileProperties' => \%fileProperties,
'filehandle' => $fh,
'buffersize' => $buffersize,
};