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Id: 24229
Status: new
Priority: 0/
Queue: Xbase

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Owner: Nobody in particular
Requestors: Stephen.Royce [...] nehta.gov.au
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Subject: Bug in open_dbf method
Date: Fri, 5 Jan 2007 15:45:00 +1000
To: <bug-Xbase [...] rt.cpan.org>
From: "Stephen Royce" <Stephen.Royce [...] nehta.gov.au>
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Pratap, I think there's a bug in the open_dbf method of the Xbase module. It is dropping the last character off the field name. The code in question (beginning at line 86 of v1.07) is: seek($self->{'DBFH'},($i-1)*32+32,0); read($self->{'DBFH'},$field_header,31); my($fname)=unpack("A*",substr($field_header,0,10)); my($null_pos)=index($fname,chr(0)); $self->{$fn}=substr($fname,0,$null_pos); $self->{$fname}=$i; The unpack conversion uses the 'A*' which strips all nulls and spaces. This means that the index search for the terminating null (chr(0)) of $fname does not find anything and returns -1, which, in turns, means that the following substr removes the last character from $fname before assigning it to $self->{$fn}. Beyond the loss of the character in the name, I think also that this may have implications for the get_field method since the field name held in $self->{$fn} and the key of $self->{$fname} (i.e, $fname itself) are not the same. I haven't needed this functionality, but scanning the code suggests that the problem will only occur if you were to access the object hash directly for the field names, searching for $self->{f-_name1}, $self->{f_name2}, etc. manually and then passing those values to get_field at a later point. Anyway, I tried this code myself and found it to work: seek($self->{'DBFH'},($i-1)*32+32,0); read($self->{'DBFH'},$field_header,31); my($fname)=unpack("A*",substr($field_header,0,10)); # # The following code is included in the Xbase module, but commented out here because of the # following bug: # # The uppercase 'A' conversion letter in unpack returns the string stripped of both nulls and # spaces. This means that the index search for chr(0) _always_ returns -1, which, in turn, # causes the following substr to drop the last character of the field name. # # my($null_pos)=index($fname,chr(0)); # $self->{$fn}=substr($fname,0,$null_pos); # # Instead, we just assign the result of the unpack directly to the field name element of the object # hash. # $self->{$fn}=$fname; # I hope this is useful. Incidentally, I am using Xbase to read .dbf files and transfer the data to a relational database (PostgreSQL in my case), creating new tables if they don't already exist. It would be enormously useful if there were some method(s) to extract the field details as (perhaps) an array of hashes like this: [ { name => <f_name1>, type => <f_type1>, length => <f_len1>, scale => <f_ldec1> }, { name => <f_name2>, type => <f_type2>, length => <f_len2>, scale => <f_ldec2> }, . . . ] I tried to create a child class to provide this additional functionality with this code: sub get_field_descriptor_arrayref { my ($self) = shift; my ($i); my $field_descriptor_arrayref = [] ; if (not ($self->{'hasdbf'})){ carp "DBF file has not been opened\n"; return undef ; } for ($i=1;$i<=$self->{'num_fields'};$i++) { my ($fn, $ft, $fd, $fl, $fld) = ("f_name$i", "f_type$i","f_disp$i", "f_len$i", "f_ldec$i"); push( @$field_descriptor_array, { name => $self->{$fn}, type => $self->{$ft}, length => $self->{$fl}, scale => $self->{$fld} } ) ; } return $field_descriptor_arrayref ; } I haven't tested it very thoroughly yet (mainly because I can't actually get the child class to work without significantly modifying the Xbase module itself - there's problems with the file handle(s) and the class that $self is blessed into) but when I incorporated it into the module code, it seemed to work okay. I had also thought of providing the option of returning the data as a hash keyed on field name, but it seemed awkward to retain the field ordering, so I haven't bothered. (You could include "position => $i", but, as I said this seems awkward and unnecessarily complicated.) If you think this is useful, please feel free to incorporate the code as you think best. I have attached my updated code to help. Cheers Stephen Royce Senior Systems Specialist Stephen.Royce@nehta.gov.au <mailto:Stephen.Royce@nehta.gov.au>
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