Main Content

CERT C: Rule DCL41-C

Do not declare variables inside a switch statement before the first case label

expand all in page

Description

Rule Definition

Do not declare variables inside a switch statement before the first case label.1

Polyspace Implementation

The rule checker checks for variable declaration before first case label.

Examples

expand all

Issue

The issue occurs when you define a variable in a switch block before the first case label.

Risk

In a switch block, control jumps to one of the case labels or a default label, depending on the control expression of the switch statement. If you define a variable before the first case label, the compiler ignores the variable declaration. Read operations on this variable can lead to indeterminate values.

Example — Noncompliant Variable Declaration
void bar(int iTemp){
	//...
}
void foo(){
	//...
	int bFlag;
	//...
	switch(bFlag){
		int temp;  //Noncompliant
		bar (temp);
	case 0:
            //...
		break;
	case 1:
            //...
		break;	
		
	}
	
}

In this example, the variable temp is declared before the first case label. The compiler ignores this declaration. If you perform a read operation on temp in one of the case blocks, the operation might lead to indeterminate values. Polyspace® flags the variable declaration.

Example — Compliant switch Statement

To fix the preceding issue, move the variable declaration out of the switch statement.

void bar(int iTemp){
	//...
}
void foo(){
	//...
	int bFlag;
	//...
	int temp;//Compliant  
	bar (temp);	
	switch(bFlag){

	case 0://...
		break;
	case 1:
		break;			
	}	
}

Check Information

Group: Rule 02. Declarations and Initialization (DCL)

Version History

Introduced in R2019a

See Also

Topics

External Websites

1 This software has been created by MathWorks incorporating portions of: the “SEI CERT-C Website,” © 2017 Carnegie Mellon University, the SEI CERT-C++ Web site © 2017 Carnegie Mellon University, ”SEI CERT C Coding Standard – Rules for Developing safe, Reliable and Secure systems – 2016 Edition,” © 2016 Carnegie Mellon University, and “SEI CERT C++ Coding Standard – Rules for Developing safe, Reliable and Secure systems in C++ – 2016 Edition” © 2016 Carnegie Mellon University, with special permission from its Software Engineering Institute.

ANY MATERIAL OF CARNEGIE MELLON UNIVERSITY AND/OR ITS SOFTWARE ENGINEERING INSTITUTE CONTAINED HEREIN IS FURNISHED ON AN "AS-IS" BASIS. CARNEGIE MELLON UNIVERSITY MAKES NO WARRANTIES OF ANY KIND, EITHER EXPRESSED OR IMPLIED, AS TO ANY MATTER INCLUDING, BUT NOT LIMITED TO, WARRANTY OF FITNESS FOR PURPOSE OR MERCHANTABILITY, EXCLUSIVITY, OR RESULTS OBTAINED FROM USE OF THE MATERIAL. CARNEGIE MELLON UNIVERSITY DOES NOT MAKE ANY WARRANTY OF ANY KIND WITH RESPECT TO FREEDOM FROM PATENT, TRADEMARK, OR COPYRIGHT INFRINGEMENT.

This software and associated documentation has not been reviewed nor is it endorsed by Carnegie Mellon University or its Software Engineering Institute.