AUTOSAR C++14 Rule M6-4-3

A switch statement shall be a well-formed switch statement

Description

Rule Definition

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

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-clause_opt}
case-label-clause-list	case-label case-clause_opt case-label-clause-list case-label case-clause_opt
case-label	`case` const-expression
case-clause	case-block-seq_opt `break` ; case-block-seq_opt `throw` assignment-expression_opt ; { statement-seq_opt `break` ; } { statement-seq_opt `throw` assignment-expression_opt ; }
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

expand all

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, Automated

Version History

Introduced in R2019a