can't happen

2 definitions found

can't happen - Free On-line Dictionary of Computing (26 May 2007) :

  can't happen
  This can't happen
  
     <programming> The traditional program comment for code
     executed under a condition that should never be true, for
     example a file size computed as negative.  Often, such a
     condition being true indicates data corruption or a faulty
     algorithm; it is almost always handled by emitting a fatal
     error message and terminating or crashing, since there is
     little else that can be done.
  
     Some case variant of "can't happen" is also often the text
     emitted if the "impossible" error actually happens.  Although
     "can't happen" events are genuinely infrequent in production
     code, programmers wise enough to check for them habitually are
     often surprised at how frequently they are triggered during
     development and how many headaches checking for them turns out
     to head off.
  
     See also firewall code, professional programming.
  
     [Jargon File]
  
     (1996-05-10)
  

can't happen - Jargon File (4.4.4, 14 Aug 2003) :

  can't happen
  
  
     The traditional program comment for code executed under a condition
     that should never be true, for example a file size computed as
     negative. Often, such a condition being true indicates data
  corruption
     or a faulty algorithm; it is almost always handled by emitting a
  fatal
     error message and terminating or crashing, since there is little else
     that can be done. Some case variant of "can't happen" is also often
     the text emitted if the `impossible' error actually happens! Although
     "can't happen" events are genuinely infrequent in production code,
     programmers wise enough to check for them habitually are often
     surprised at how frequently they are triggered during development and
     how many headaches checking for them turns out to head off. See also
     firewall code (sense 2).