MISRA C++:2008 Rule 7-5-1

A function shall not return a reference or a pointer to an automatic variable (including parameters), defined within the function

Description

Rule Definition

A function shall not return a reference or a pointer to an automatic variable (including parameters), defined within the function.¹

Rationale

Local objects of a function are destroyed at the end of a function call. If you return the address of such an object via a pointer, you might access a destroyed object. For instance:

int* foo(int a){
	int b = a^2;
	return &b;
}

The function foo() returns a pointer to b. The variable b goes out of scope at the end of the function call and the pointer returned by foo() points to a destroyed object. Accessing the pointer leads to undefined behavior.

Polyspace Implementation

Polyspace^® raises a violation if a function returns a reference or pointer to a variable that goes out of scope at the end of the function call.

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

Avoid Returning Pointers to Local Variables

int gVal;
//...

int* foo(void){
	int val;
	//...
	return &val;//Noncompliant
}

In this example, the function foo() returns the address of val. This local variables goes out of scope at the end of the function call. Accessing the pointer returned by foo() results in undefined behavior. Polyspace raises a violation.

Check Information

Group: Declarations

Category: Required

Version History

Introduced in R2013b

R2022b: Checker allows returning of pointers passed to function

The rule checker no longer reports a violation if a function returns a pointer or reference that is passed to the function as a parameter. For instance:

int* func(int* param){
	int* localCopy = param;
	//...
	return localCopy;//Compliant
}