C attribute: fallthrough (since C23)
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Indicates that the fall through from the previous case label is intentional and should not be diagnosed by a compiler that warns on fallthrough.
Syntax
[[ fallthrough ]][[ __fallthrough__ ]]
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Explanation
May only be used in an attribute declaration to create a fallthrough declaration ([[fallthrough]];).
A fallthrough declaration may only be used in a switch statement, where the next block item (statement, declaration, or label) to be encounted is a statement with a case or default label for that switch statement.
Indicates that the fall through from the previous case label is intentional and should not be diagnosed by a compiler that warns on fallthrough.
Example
Run this code
#include <stdbool.h> void g(void) {} void h(void) {} void i(void) {} void f(int n) { switch (n) { case 1: case 2: g(); [[fallthrough]]; case 3: // no warning on fallthrough h(); case 4: // compiler may warn on fallthrough if(n < 3) { i(); [[fallthrough]]; // OK } else { return; } case 5: while (false) { [[fallthrough]]; // ill-formed: no subsequent case or default label } case 6: [[fallthrough]]; // ill-formed: no subsequent case or default label } } int main(void) {}