Delete last line of a textfile without putting the whole file in memory

Question

Hello!
I want to delete the last line of a text file without loading the whole text file into thememory. My problem is as follows:
A algorithm generates output that has to be written into a text file. This happens periodically - the output goes straight into a xml file. The xml file looks like this:
<test>
<step>
<time>2006-06-19 10:55:20</time>
<result>12321</result>
</step>
<step>
<time>2006-06-19 10:58:20</time>
<result>41515</result>
</step>
</test>
The XML file must be valid, so I have to delete the last line ("</test>") before I add a new <step>-section.
Many thanks in advance
Kind regards,
buliwyf

Answer 1

For processing in a separate tool which understands XML, then using a DTD to declare an external entity is often better - you wrap the entity in the document root element, so you can just append to the end of the file the entity references and not bother about inserting before the closing tag.
File other app loads:
<?xml version="1.0"?>
<!DOCTYPE test [ <!ENTITY content SYSTEM "content.xmlfragment"> ]>
<test>&content;</test>File content.xmlfragment which can be simple appended to:
<step time="2006-06-19 10:55:20">12321</step>
<step time="2007-04-09 10:55:20">12321</step>
<step time="2008-09-26 00:03:20">12321</step>If you can't use XML to solve the problem, then you can scan backwards in the file (using random access file or file buffer) until you find a '<' character which is followed by an '/' character. You can't have CDATA after the closing tag of the document element, and comments and processing instructions have different characters following the '<'.