(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() break caSe PINK: do_pink() /* FALL THROUGH */ caSe RED: do_red() break default: do_blue() break } 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 iSconSidered 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.
