"Empty Stream" error as result of repeated reading of __DATA_

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

Hello all,

I am getting the LibXML error "Empty Stream". I suspect it has something to do with the fact that I am reading the XML from the __DATA__ block for a second time within the script.

Does anyone know if problems can arise if the __DATA__ block is read multiple times?

Thanks,

loris

Comment on "Empty Stream" error as result of repeated reading of __DATA__ block?

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Re: "Empty Stream" error as result of repeated reading of __DATA__ block? by gellyfish (Monsignor) on Aug 17, 2005 at 08:05 UTC
Yes, if you want to read the from the DATA filehandle more than once you need to rewind it to the beginning. Something like: `use Fcntl; + my $where = tell(DATA); while(<DATA>) { print; } + seek DATA, $where, SEEK_SET; + while(<DATA>) { print; } __DATA__ 1 2 3 4 5 6 7` [download] The reason you have to get the position of the filepointer in `DATA` with `tell` is that the `DATA` filehandle actually refers to the whole program file and is simply left at the beginning of the stuff after the `__DATA__` after perl has finished reading in the program - thus if you do `seek DATA, 0, SEEK_SET` you will be at the start of the program text. /J\	[reply] [d/l] [select]
Re^2: "Empty Stream" error as result of repeated reading of __DATA__ block? by NateTut (Deacon) on Aug 17, 2005 at 12:29 UTC
I might also point out that you must rewind regular files too in order to read from them again once you have reached EOF. Also I believe that `use Fcntl ':seek';` will clear up your warning.	[reply] [d/l] [select]
Re^2: "Empty Stream" error as result of repeated reading of __DATA__ block? by loris (Hermit) on Aug 17, 2005 at 08:35 UTC
Thanks very much, gellyfish, that was just what I needed. However, your code does produce a warning: `Argument "SEEK_SET" isn't numeric in seek at ./test.pl line 13, <DATA> + line 7.` [download] on my system, which I don't understand, SEEK_SET being a constant after all. Do you know why this occurs? Thanks again, loris	[reply] [d/l]
Re^3: "Empty Stream" error as result of repeated reading of __DATA__ block? by gellyfish (Monsignor) on Aug 17, 2005 at 10:55 UTC
Er, no I don't know why this occurs - it is possible that you didn't `use Fcntl` and are not using `strict`. If you are worried by this you can use `0` instead but this is not guaranteed to be portable to all systems. /J\	[reply] [d/l] [select]