Reading a (BIG) text file one line at a time - in reality...

Richard Gaskin ambassador at fourthworld.com
Wed Nov 24 05:36:38 EST 2004


xbury.cs at clearstream.com wrote:
>>We still don't know the business specifics of the original poster to
>>know if this is at all useful to him, but assuming it will be to others
>>down the road the next logical questions are:
>>
>>1. How can we generalize this so one handler can be used to feed lines
>>to another handler for processing?
>>
>>2. Can we further generalize it to use other chunk types (words, items,
>>tokens)?
>>
>>3. Once we solve #1 and 2, should we request an addition to the engine
>>for this?  If you think this is fast now wait till you see what the
>>engine can do with it.  It'll be like life before and after the split
>>and combine commands.
 >
 > There is also the issue with the buffer size which can significantly
 > reduce the number of file reads (depending on block size, file size,
 > number of words or lines or etc to be parsed)... There's different
 > optimizations for this to be considered and usually on case by case
 > basis. It's hard to generalize.

Good thought. Yes, if we could generalize a handler we should have a 
param for bufferSize.

 > Can you expand on 1 and 2? Im not sure what you mean?
 >
 > Do you mean
 >
 > read from file for a word -- or for a line
 >  or something like that?

Exactly.

Maybe such a handler could look like this:

   ReadBuffered pFileName, pChunkType, pCallbackMessage, pBufferSize

Your routine calls ReadBuffered and the ReadBuffered command sends the 
callback message to you with the next chunk as its param.

Here's a challenge:  can we implement callbacks in a way that don't use 
"send"? It's not prohibitively slow, but if we're doing this for speed 
it'd be nice if we could add the convenience of a separate handler 
without sacrificing any milliseconds we don't need to.

-- 
  Richard Gaskin
  Fourth World Media Corporation
  ___________________________________________________________
  Ambassador at FourthWorld.com       http://www.FourthWorld.com


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