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Full Discussion: Very Basic Question regarding "while" loop
Top Forums Shell Programming and Scripting Very Basic Question regarding "while" loop Post 302423701 by gaurav1086 on Friday 21st of May 2010 06:34:43 PM
Old 05-21-2010
hello,

This seems to be implementation dependant. When a process opens a file for reading/writing, the operating system loads a chunk of the file in memory for the process to read/write. So when the process has done reading with that chunk, the OS loads another chunk. This is implementation dependant.

I tried the opposite, as the while loop was executing, I added a few more entries to the end of the file(cat >> file) and while read them all. So while has a dynamic behaviour which is OS dependant.

So I can conclude that it depends on two factors - 1. size of the file 2.OS policy.
However this behaviour will cause haphazard results. Its unpredictable way to achieve things.

Regards,
gaurav.
 

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LEARN ABOUT DEBIAN

zipios_backbuffer

zipios::BackBuffer(3)					     Library Functions Manual					     zipios::BackBuffer(3)

NAME

       zipios::BackBuffer -

       A BackBuffer instance is useful for reading the last part of a file in an efficient manner, when it is not known exactly how far back
       (towards the front!) to go, to find the start of the desired data block.

SYNOPSIS

       #include <backbuffer.h>

       Inherits vector< unsigned char >.

   Public Member Functions
       BackBuffer (istream &is, VirtualSeeker vs=VirtualSeeker(), int chunk_size=1024)
	   BackBuffer constructor.
       int readChunk (int &read_pointer)
	   Reads another chunk and returns the size of the chunk that has been read.

Detailed Description
       A BackBuffer instance is useful for reading the last part of a file in an efficient manner, when it is not known exactly how far back
       (towards the front!) to go, to find the start of the desired data block.

       BackBuffer is a vector< unsigned char > that fills itself with data from a file by reading chunks from the end of the file progressing
       towards the start. Upon construction the BackBuffer instance is associated with a file and a chunksize can be specified. To read a chunk of
       the file into the BackBuffer call readChunk().

       Definition at line 32 of file backbuffer.h.

Constructor &; Destructor Documentation
   zipios::BackBuffer::BackBuffer (istream &is, VirtualSeekervs = VirtualSeeker(), intchunk_size = 1024) [inline, explicit]
       BackBuffer constructor. Parameters:
	   is The istream to read the data from. The stream must be seekable, as BackBuffer will reposition the file position to read chunks from
	   the back of the file.
	   chunk_size specifies the size of the chunks to read the file into the BackBuffer in.

       Exceptions:
	   FCollException Thrown if the VirtualSeeker vs that has been specified is invalid for the istream is.

       Definition at line 61 of file backbuffer.h.

Member Function Documentation
   int zipios::BackBuffer::readChunk (int &read_pointer) [inline]
       Reads another chunk and returns the size of the chunk that has been read. Returns 0 on I/O failure.

       Parameters:
	   read_pointer When a new chunk is read in the already stored bytes change position in the BackBuffer. read_pointer is assumed by
	   readChunk() to be a pointer into a position in the BackBuffer, and is updated to point to the same position in the file as it pointed
	   to before the new chunk was read.

       Definition at line 75 of file backbuffer.h.

Author
       Generated automatically by Doxygen for Zipios++ from the source code.

Zipios++							  Mon Oct 10 2011					     zipios::BackBuffer(3)
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