A switch statement shall be considered to be well-formed if it conforms to the subset of C switch statements that is specif ed by the following syntax rules. If a syntax rule given here has the same name as one defined in The Standard then it replaces the standard version for the scope of the switch statement; otherwise, all syntax rules given in The Standard are unchanged.

switch-statement:
  switch ( switch-expression ) { case-label-clause-list final-default-clause-list } 
  switch ( switch-expression ) { initial-default-clause-list case-label-clause-list }

case-label-clause-list:
  case-clause-list 
  case-label-clause-list  case-clause-list 

case-clause-list:
  case-label switch-clause 
  case-label case-clause-list

case-label:
  case constant-expression:

final-default-clause-list:
  default:   switch-clause 
  case-label final-default-clause-list

initial-default-clause-list:
  default: switch-clause 
  default: case-clause-list

switch-clause:
  statement-list_opt break;
  C90: {declaration-list_opt statement-listopt break; } 
  C99: { block-item-list_opt  break; }

Except where explicitly permitted by this syntax, the case and default keywords may not appear anywhere within a switch statement body.

Note: some of the restrictions imposed on switch statements by this rule are expounded in the rules referenced in the “See also” section. It is therefore possible for code to violate both this rule and one of the more specific rules.

Note: the term switch label is used within the text of the specific switch statement rules to denote either a case label or a default label.

Rationale

The syntax for the switch statement in C is not particularly rigorous and can allow complex, unstructured behaviour. This and other rules impose a simple and consistent structure on the switch statement.

Example

The remaining rules in this section give examples that are also relevant to this rule.