MISRA C++:2008 Rule 6-4-3

A switch statement shall be a well-formed switch statement

Description

Rule Definition

A switch statement shall be a well-formed switch statement.¹

Rationale

In addition to the C++ standard syntax rules, MISRA defines their own syntax rules for creating well-formed switch statements. These additional syntax rules create a consistent structure for switch statements.

The additional MISRA syntax rules include:

Rule	Syntax
switch-statement	switch (condition) {case-label-clause-list default-label-clauseopt}
case-label-clause-list	case-label case-clauseopt case-label-clause-list case-label case-clauseopt
case-label	case const-expression
case-clause	case-block-seqopt break ; case-block-seqopt throw assignment-expressionopt ; { statement-seqopt break ; } { statement-seqopt throw assignment-expressionopt ; }
default-label-clause	default-label default-clause
default-label default-clause	default : case-clause
case-block	expression_statement compound_statement selection_statement iteration_statement try_block
case-block-seq	case-block case-block-seq case-block

These terms from the table are defined as such:

• switch-label — Either a case-label or default-label.

• case-clause — The code between any two switch-labels.

• default-clause — The code between the default-label and the end of the switch statement.

• switch-clause — Either a case-clause or a default-clause.

The MISRA C++ switch syntax rules do not include the following statements, but do permit them within the compound statements that form the body of a switch-clause statement.

• labelled_statement

• jump_statement

• declaration_statement

Polyspace Implementation

The rule checker reports a violation in these situations:

• A statement occurs between the switch statement and the first case statement.

  For instance:

  switch(ch) {
    int temp;
    case 1:
      break;
    default:
      break;
  }

• A label or a jump statement such as goto or return occurs in the switch block.

• A variable is declared in a case statement that is outside any block.

  For instance:

  switch(ch) {
    case 1: 
      int temp;
      break;
    default:
      break;
  }

Troubleshooting

If you expect a rule violation but Polyspace^® does not report it, see Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

Adhere to MISRA Rules for Well-Formed Switch Statements

The example fails to follow two of the well-formed switch statement rules from MISRA.

• The statement int temp; occurs between the switch statement and the first case statement.

• case 2 contains a return statement.

Polyspace reports a single violation for the entire switch statement despite multiple violations within the switch statement.

int example(int x)
{
	switch (x) {			//Noncompliant
		int temp;
		case 0:
			break;
		case 1:
		case 2:
			return x;
		default:  
			break;
	}

	return x;
}

Check Information

Group: Statements

Category: Required

Version History

Introduced in R2013b