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  Rule 12.2: Accessing volatiles in simple assignment statemnt
Posted by: joa07 - 30-01-2009, 09:44 AM - Forum: 6.12 Expressions - Replies (7)

Hi!

It is stated in the MISRA-C:2004 rule 12.2 (required) that "...it is recommended that volatiles only be accessed in simple assignment statements, such as the following:"

Code:
volatile uint16_t v;
/* ... */
x = v;
Is this recommendation a part of the MISRA-C:2004 12.2 rule, or is it just a common recommendation?
Should a MISRA-C:2004 analysis tool try to enforce this kind of assignment statement?

Is the following statement part of the "simple assignment statements" philosophy (I think so)?
Code:
volatile uint32_t *v = AN_ADDRESS;
/* ... */
*v = x;

The reason for this question is that our current analysis tool raises a MISRA-C:12.2 violation for the last code snippet above, and I think this is a misinterpretation of the guidelines.

//JOA

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  Clarification for 6-5-1
Posted by: pkruk - 12-01-2009, 10:21 AM - Forum: 6.5 Expressions (C++) - Replies (1)

Quote:A for loop shall contain a single loop-counter which shall not have floating type.

Is following code compliant?

Code:
void foo() {
    const char * x = "Foo";
    for (const char * ptr = x; *ptr; ++ptr) { // Compliant?
        // ...
    }
}

In my opinion the loop-control-variable (ptr) is not "an operand to a relational operator in condition" (the variable pointed to by the ptr is the operand) so it does not meet conditions for a loop-counter.

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  Clarification for 7–5–1
Posted by: pkruk - 12-01-2009, 09:48 AM - Forum: 6.7 Declarations (C++) - Replies (1)

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

I have a question about reference types. Is the following code compliant or not?


Code:
int global_var;

int & foo(int & ref) {
    return ref;             // Compliant?
    
    int & global_ref = global_var;
    return global_ref;      // Compliant?
    
    int local_var;
    int & local_ref = local_var;
    return local_ref;       // Compliant?
}

int * bar(int & ref) {
    return &ref;            // Compliant?

    int & global_ref = global_var;
    return &global_ref;     // Compliant?
    
    int local_var;
    int & local_ref = local_var;
    return &local_ref;      // Compliant?
}
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  Realizing f strong typing
Posted by: B3NN7 - 10-01-2009, 02:48 PM - Forum: General Questions - Replies (1)

Hello,

I have a problem by realizing a strong typed library function. The library function shall get a pointer to one byte and the number of bytes up on the pointer to be read.

But I does have the requirement that only local variables on the stack or global variables at the data area of the C Application may be processed by my function.

Here is a bad example:

Code:
void function(const void* const Data_pv, const uint8_t Size_u8)
{
   ...
}

void* Address = 0xFFAF;

function(Address, 8);

It shall not be possible to pass a pointer on void.

Here is a good example

Code:
uint32_t Data_u32 = 5;

function( (uint8_t*)&Data_32, sizeof(Data_u32));

Is there a rule of MISRA C supporting me by realizing my described problem ?

Thanks B3NNY

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  Example for Rule 12–1–1
Posted by: pkruk - 24-12-2008, 11:34 AM - Forum: 6.12 Special member functions (C++) - Replies (1)

Hello,

I'm not sure if the example for this rule is correct in one case. Simplified code:

Code:
class B2
{
public:
virtual ~B2 ( );
B2 ( )
{
typeid ( B2 ); // Non-compliant
}
};

Why is this typeid non compliant? It does not use object’s dynamic type so it should not be a violation of the rule. This is similar to using typeid on e.g. not polymorphic type, which is allowed by the rule. ISO/IEC 14882:2003(E) standard:

Quote:5.2.8
3. When typeid is applied to an expression other than an lvalue of a polymorphic class type, the result
refers to a type_info object representing the static type of the expression. [...]
4. When typeid is applied to a type-id, the result refers to a type_info object representing the type of the
type-id. [...]
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  Rule 8.10 and init functions
Posted by: Christoph - 28-11-2008, 09:41 AM - Forum: 6.8 Declarations and Definitions - Replies (2)

Hi,

usualy when a C module is designed (at our company), it consists of at least one external function. An example:

module.h:
extern void initModule()
extern void setData(uint8_t data)
extern uint8_t getData()

now initModule() is called in main (once in the whole software), as it is an init function. From a design point of
view module.* is the right place for initModule(), but Misra suggests to define it in main, since it is only called there.
I think this is bad design and not always possible (e.g. because module variables are hidden and not accessible form main).

So what is your recommendation in such a case? Is there a best practice for this pattern?

Best Regards
Christoph

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  Rule 18-4-1 (ban of dynamic heap memory allocation)
Posted by: shanz - 29-09-2008, 09:28 AM - Forum: 6.18 Language support library (C++) - Replies (1)

One of the most commonly quoted advantages of object orientation is polymorphism.
C++ often relies on dynamically allocated pointers to achieve (run-time) polymorphism.

How can polymorphism be achieved without resorting to dynamic memory allocation?
I suspect that preallocating pointers on the stack is the answer but can someone please write some example code?

Thanks.

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  Incorrect comment in mc2_1703.c
Posted by: Graham Andrews - 17-09-2008, 01:27 PM - Forum: MISRA-C:2004 Exemplar Suite - Replies (1)

There is a comment regarding line:

Code:
else if ( ( &array_12 [ 12 ] - &array_12 [ index_1 ] ) > 0 )
The comment states that this line violates rule 17.4, which is not the case, as the variable array_12 has been declared as an array.
It should state that there is a violation of rule 21.1 regarding array bound errors.

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  Can I get by with a little help from My Friends?
Posted by: gs - 12-09-2008, 06:50 PM - Forum: 6.11 Member access control (C++) - Replies (1)

Rule 11-0-1 states,

Quote:Member data in non-POD class types shall be private.
with the rationale:
Quote:By implementing class interfaces with member functions, the implementation retains more control over how the object state can be modified, and helps to allow a class to be maintained without affecting clients.
Does the above mean non-POD structure types should not contain any friend declarations? A friend declaration would by definition allow for the circumvention of the access restrictions.

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  Proverbially Playing the `Devil's Advocate' for Rule 15-1-2
Posted by: gs - 11-09-2008, 06:46 PM - Forum: 6.15 Exception handling (C++) - Replies (1)

The text and rationale of rule 15-1-2 make no mention of the word `macro'. Let us suppose an application made no reference to the Standard Library within it's source code. Consequently, the `NULL' macro has not been defined. Would the following code violate rule 15-1-2?

Code:
class A {};
A NULL;
void f()
    {
    throw NULL;
    }
The very premise of the rationale for the rule is invalid. In this case a `throw NULL;' is not equivalent to `throw (0);' and is not a throwing of an integer expression.

Furthermore, the wording of the rationale is slightly incorrect:
Quote:throw(NULL) (equivalent to throw(0)) is never a throw of the null-pointer-constant ...
To quote ISO C++, 18.1, para. 4, (lib.support.types):
Quote:The macro NULL is an implementation-defined C++ null pointer constant in this International Standard
(4.10).
Granted, the referenced `4.10' states a null pointer constant has integer (not pointer) type. However, the macro is a null pointer constant.

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