Dynamic Arrays?!

 BBS: Inland Empire Archive
Date: 05-19-92 (11:36)             Number: 136
From: TIM FITZGERALD               Refer#: NONE
  To: DAVE CLEARY                   Recvd: NO  
Subj: Dynamic Arrays?!               Conf: (2) Quik_Bas
DC>Garbage collection is done on far memory and dynamic arrays. For instance,
DC>say you are allocating and deallocating many dynamic
DC>arrays. After a while, far memory will be fragmented. If QB
DC>did not do a garbage collection, You could end up with alot
DC>of useless memory. I do not know what triggers it. It might
DC>be when QB can not allocate an array because of memory
DC>fragmentation, or it might be more often than that.

  I may be jumping in here, without knowing the full thread of this
  message.. so if the rest of my reply is out of place, then please
  ignore. :)

  This snippet was taken out of a book called "Advanced QuickBasic 4.0"
  by Murray Lesser. ISBN 0-553-34546-X (p.184)

  "...Initially, all string descriptors point to null strings, each of
  zero length with a dummy string-space address. When a value is
  assigned to a string variable during run time, that value (along with
  some internal bookkeeping code) is written into string space at the
  first available location (starting from the bottom of string space),
  and the proper length and address data ware written into the
  corresponding string descriptor. If any previously assigned string
  value is modified, the old value in string space is marked as invalid,
  a new value is written at the current tip of used string space, and
  the corresponding string descriptor is updated accordingly.

      Eventually, there may not be any more string space available when
  it becomes time to write a new value, so the string-space manager
  reclaims the invalid string space by moving all still-valid values to
  the bottom of string space, changing their descriptors accordingly,
  and resetting the current "top of used string space" to the end of the
  still-valid values. The technical term for this reclamation is garbage

  If this info isn't of any use to you Dave, or you Matt, then hopefully
  it will be of use to someone. Even though the book is copyrighted, I
  don't thing quotes from the book will violate the copyright? ;)


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