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Meaning of FALL THROUGH

Pronunciation:  fol throo

 
Computing Dictionary
 
 Definition: 

(The American misspelling "fall thru" is also common)

1. To exit a loop by exhaustion, i.e. by having fulfilled its exit condition rather than via a break or exception condition that exits from the middle of it. This usage appears to be *really* old, dating from the 1940s and 1950s.

2. To fail a test that would have passed control to a subroutine or some other distant portion of code.

3. In C, "fall-through" occurs when the flow of execution in a switch statement reaches a "case" label other than by jumping there from the switch header, passing a point where one would normally expect to find a "break". A trivial example:

        switch (colour)
        case green:
          do_green

The effect of the above code is to "do_green()" when colour is "GREEN", "do_red()" when colour is "RED", "do_blue()" on any other colour other than "PINK", and (and this is the important part) "do_pink()" *and then* "do_red()" when colour is "PINK". Fall-through is considered harmful by some, though there are contexts (such as the coding of state machines) in which it is natural; it is generally considered good practice to include a comment highlighting the fall-through where one would normally expect a break. See also duff's device.

 
Thesaurus Terms
 
 Related Terms: break down, collapse, come to naught, come to nothing, crash, fall, fall dead, fall down, fall flat, fall in, fall short, fall stillborn, fizzle out, get bogged down, get hung up, get mired, go to smash, peter out, poop out
 

 

 

 

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