C++ attribute: fallthrough (since C++17)

 

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Attributes

assume (C++23)

carries_dependency (C++11)

deprecated (C++14)

fallthrough (C++17)

indeterminate (C++26)

likely (C++20)

maybe_unused (C++17)

nodiscard (C++17)

noreturn (C++11)

no_unique_address (C++20)

optimize_for_synchronized (TM TS)

unlikely (C++20)

 

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]]

Explanation

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.

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

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
  }
}

See also

C documentation for fallthrough