Indicates that the fall through from the previous case label is intentional and should not be diagnosed by a compiler that warns on fallthrough.
[[fallthrough]] |
May only be applied to a null statement to create a fallthrough statement ([[fallthrough]];).
A fallthrough statement may only be used in a switch statement, where the next statement to be executed is a statement with a case or default label for that switch statement. If the fallthrough statement is inside a loop, the next (labeled) statement must be part of the same iteration of that loop.
void f(int n)
{
void g(), h(), i();
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: next statement is not
// part of the same iteration
}
case 6:
[[fallthrough]]; // ill-formed, no subsequent case or default label
}
}The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| CWG 2406 | C++17 | [[fallthrough]] could appear in a loopnested inside the target switch statement | prohibited |
C documentation for fallthrough |
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