AUTOSAR C++14 Rule M7-1-2

A pointer or reference parameter in a function shall be declared as pointer to const or reference to const if the corresponding object is not modified

Description

Rule Definition

A pointer or reference parameter in a function shall be declared as pointer to const or reference to const if the corresponding object is not modified.

Rationale

Best practice for function signature is to clearly communicate whether passing an object to the function by parameter results in a modification of the object. Consider these function signatures:

void foo(const in&);
void bar(int&);

Here, foo() accepts an integer as a const reference, which clearly communicates that the input reference is not modified by foo(). From the signature of bar(), it is not clear whether the input reference is modified or not.

To comply with this rule, const-qualify the type of named pointer or reference parameters. As an exception, this rule does not apply if a parameter is modified by any of the functions in a set of overriding functions.

Polyspace Implementation

The checker flags non-const pointer parameters if the underlying object is not modified in the function body.

If a pointer parameter is passed to another function as a non-const reference or pointer, the checker assumes that the parameter can be modified. Such parameters are not reported as violations.

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

Non-const Pointer Parameter Not Modified

In this example, the parameters *b and *c are not modified in the function and they are not qualified as const. Polyspace reports violations of this rule.

void sum(int *a, int *b, int *c, const int *d) { //Noncompliant
	*a = *b + *c + *d;

}

Check Information

Group: Declaration

Category: Required, Automated

Version History

Introduced in R2019a

R2024b: Violation not reported if parameter modified by any overriding function

Polyspace does not report a violation of this rule on a virtual function that has a non-const reference parameter if any of its overriding functions modify the parameter.

R2024a: Checker correctly handles calls to variadic functions

The rule checker does not report a violation on a pointer parameter if the parameter is passed on further to a variadic function. The reason is that you might not be able to declare such a pointer as pointer to const. For instance, in this example, the checker does not report a violation on the pointer parameter buff of the function fill_buffer() because the parameter is further passed to the function snprintf() that might modify the pointed value:

#include <cstdlib>
#include <cstdio>


int fill_buffer(char * const buff, const size_t sizeOfBuff){
    const int id = rand() % sizeOfBuff;
    return ::snprintf(buff, sizeOfBuff, "%d", id);
}

Previously, a violation would be reported because variadic functions such as snprintf() were not handled correctly.