-Wimplicit-fallthrough in GCC 7

In C and C++, the cases of a switch statement are in fact labels, and the switch is essentially a go to that jumps to the desired label. Since labels do not change the flow of control, one case block falls through to the following case block, unless terminated by a return, a break, a no return call or similar. In the example below, “case 1” falls through to “case 2“:

switch (cond)
   {
   case 1:
     a = 1;
   case 2:
     a = 2;
     break;
   /* ... */
   }

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