C attribute: fallthrough (since C23)

Indicates that the fall through from the previous case label is intentional and should not be diagnosed by a compiler that warns on fallthrough.

[edit] Syntax

[edit] 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.

[edit] Example

#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) {}

[edit] See also

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