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  Rule 11-0-1 and POD types
Posted by: cgpzs - 24-03-2021, 01:57 PM - Forum: 6.11 Member access control (C++) - Replies (1)

Hi,

I have a few questions about rule M11-0-1:

Rule 11–0–1
(Required)
Member data in non-POD class types shall be private.

* As posted in a previous question, "class types" here means "class, struct or union". Is my understanding correct?
* Why should the fact that a type is POD or not influence access control?

Let's have the following controversial example. Having the following POD type:

Code:
struct Foo
{  
   int x;
   int y;
};

The design for this struct is to aggregate 2 variables together, but there's no invariance to hold. x and y can vary independently. The struct is POD, so it's compliant with M11-0-1.

Now, in the future we want to extend `Foo` with another variable independent from x and y:

Code:
struct Foo
{
    int x;
    int y;
    std::string name;
};

Now, since `Foo` contains a `std::string`, and `std::string` is not a POD, then `Foo` becomes a non-POD. In turn, this now violates M11-0-1, which forces us to make these fields private. This leads to adding trivial boilerplate getters and setters to `Foo`, and every consumer of this struct needs to change their way of interacting with `Foo`.

This wouldn't happen if `name` was a `char const*`:

Code:
struct Foo
{
    int x;
    int y;
    char const* name;
};

The semantics of `Foo` are identical to before, just using a different type for one of its members. Why should that lead to such dramatic changes?

A similar example:

Code:
struct Bar
{
    std::vector points_x;
    std::vector points_y;
};

`Bar` is a collection of points that are independent from each other; there's no invariant.

Besides, POD types are types that are "compatible with the types used in the C programming language". Why should this be a concern if we are programming in C++? Why should we make our structs "C-compatible", if they are meant to be used in C++ code?

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  choosing C compiler
Posted by: scb1993 - 04-03-2021, 02:11 AM - Forum: General Questions - Replies (1)

Hello Sir,

I was going through MISRA C 2012 rules, Does MISRA says any guidelines to choose compiler for C as there are many compilers available in the market.

Regards
Subhra

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  MISRA C:2012 permits published
Posted by: david ward - 01-03-2021, 02:28 PM - Forum: Announcements - No Replies

The MISRA C:2012 Permits are now available as a free download from the "Resources" section of this Bulletin Board.

The MISRA C:2012 Permits presents a number of deviation permits covering commonly-encountered use cases for use with the MISRA C:2012 guidelines. It should be used in conjunction with MISRA Compliance:2020, a companion document which describes the purpose of deviation permits and which sets out the principles by which the concept of MISRA Compliance is governed.

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  MISRA C:2012 permits
Posted by: david ward - 01-03-2021, 01:22 PM - Forum: MISRA resources - No Replies

No sooner had the MISRA C:2004 Permits been published, the question was asked “When will MISRA C:2012 Permits be published?” The wait is now over ...

MISRA C:2012 Permits provides a set of permits to aid compliance, particularly in the lower-levels (e.g. hardware access), but also to make compliance easier where automatically generated code is being created.

A related Guideline Reclassification Plan for Automatically Generated Code is being worked on, and will be released in due course.

This document presents a number of deviation permits covering commonly-encountered use cases for use with the MISRA C:2012 guidelines. It should be used in conjunction with MISRA Compliance:2020, a companion document which describes the purpose of deviation permits and which sets out the principles by which the concept of MISRA Compliance is governed.

The number of deviation permits within this document is expected to grow and it is possible that existing deviation permits may be revised. The document contains a table with a record of these changes.

The current release is Edition 1, published March 2021.



Attached Files
.pdf   MISRA C 2012 Permits (First Edition).pdf (Size: 269.03 KB / Downloads: 85)
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  6-5-4: on variable or expression?
Posted by: Nadege - 29-01-2021, 11:06 AM - Forum: 6.6 Statements (C++) - Replies (1)

Hello,

6-5-4 says "The loop-counter shall be modified by one of: --, ++, - = n, or + = n; where n remains constant for the duration of the loop"

Should this code below raise 6-5-4?

int main() {
int k = 8;

for (int j = 0; j < 10; j += k + 3) {
}
}

If 'n' concerns variable only, I would say 'Yes'.
If 'n' concerns expressions, I would say 'No'.

What do you think?
Thanks in advance for your help.

Nadège

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  MISRA AC guidelines public review Jan 21
Posted by: david ward - 22-01-2021, 04:34 PM - Forum: MISRA AC GMG discussions - No Replies

MISRA is pleased to announce that drafts of new versions of its Autocode documents MISRA AC GMG "Generic Modelling Design and Style Guidelines" and MISRA AC SLSF "Modelling Design and Style Guidelines for the Application of Simulink and Stateflow" will shortly be available for public review.

The revision process has focused on the following:

  • Addressing feedback raised on the previous versions
  • Seeking to reduce areas of ambiguity and inconsistency
  • Updating SLSF for more recent revisions of the MathWorks toolset with expanded capabilities and, in some areas, modelling semantics
  • Further clarifying and extending Stateflow usage guidelines to define more tightly a standardized usage style from a subset of Stateflow’s capabilities

If you would like to be considered as a reviewer please download the attached file and return it to us via email. We will review applications and be in touch with next steps in due course. Please note that in the case of high levels of interest we may not be able to accept all offers of reviews.

Updated Feb 2021. The call for reviewers is now closed and we will be sending out the review package shortly. Thank you to everyone that has expressed interest

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  Rule 10.4 and essentially signed integer constant expressions
Posted by: jaska - 19-01-2021, 02:34 PM - Forum: 8.10 The essential type model - Replies (1)

Rule 10.3 exception 1 allows assigning a signed integer constant expression to an essentially unsigned type, if the value can be represented in that type; u8 = 2 * 24; is allowed.
Rule 10.4 has no such exception
Expressions like u32 > 0, u8 != 0, and u32 += 1 violate rule 10.4.

Now:

uint32_t u32idem(uint32_t x) { return x; }
bool less_u32(uint32_t a, uint32_b ) { return a < b; }

if (u32 < u32idem(1)) { /* accepted by 10.3 and 10.4 */
} else if (less_u32(u32, 3)) { /* accepted by 10.3 (and 10.4) */
} else if (u32 < 4u) { /* fine by 10.4 */
} else if (u32 < 7) { /* violates 10.4 */
} else if (11u > u32) { /* ok, remove u and it's not */
} else {
switch (u32) {
case 23: /* ok */
...

Why are binary operators handled differently from assignments and switch cases? I think the exception should be the same for both 10.3 and 10.4 ?

Why is there no exception for Rule 10.4 allowing an integer constant expression to be used in a binary expression?

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  10.4 violation for u8b + 2
Posted by: fmteau - 18-01-2021, 01:27 PM - Forum: 8.10 The essential type model - Replies (2)

Hello MISRA Bulletin Board,

I understand mixing signed and unsigned variables in arithmetic operations can really lead to unexpected results,
but I really fail to see what is the risk in adding a constant value of 2 (SLTR of signed char) to an unsigned 8-bit (char) variable.

Could you please elaborate what can possibly go wrong in this case?

Thanks in advance.

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  No operators in #if
Posted by: John C - 17-12-2020, 08:29 AM - Forum: 8.10 The essential type model - Replies (8)

The MISRA checker I am using is rejecting operators in #if as noted in the following code.

Code:
#define TRUE 1

#define Condition1 TRUE
#define Condition2 TRUE

#if Condition1   /* Accepted */
#endif
#if !Condition1  /* Rejected */
/* Rejection is because:
Unpermitted operand to operator '!' [MISRA 2012 Rule 10.1, required]
*/
#endif
#if Condition1 && Condition2  /* Rejected */
/* Rejection is because:
Unpermitted operand to operator '&&' [MISRA 2012 Rule 10.1, required]
*/
#endif
#if Condition1 || Condition2  /* Rejected */
/* Rejection is because:
Unpermitted operand to operator '||' [MISRA 2012 Rule 10.1, required]
*/
#endif
According to the supplier, the constant '1' (or '0' when used in the same way) is being interpreted as a signed int and therefore the operators '!', '&&' and '||' cannot be used with it.

Is the checker's interpretation correct?

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  MISRA C:2012 9.3 clarification
Posted by: mcks - 24-11-2020, 09:19 AM - Forum: 8.9 Initialization - Replies (1)

I try to implement the checks for "9.3 - Arrays shall not be partially initialized" in Cppcheck, and would like to have some clarifications.

Is it ok to mix initializers like this, as long as every element gets initialized?

int32_t a[3] = { 1, 2, [2]=3 };

For multi-dimensional arrays, this would be compliant:

int32_t b[2][2] = { { 1, 2 }, { [1]=4 } };

beacuse b[1] is initialized with only a designated initializer.


As for c, both the array subobjects c[0] and c[1] are fully initialized, but there is no initialization of c[2]. Does that make the statement non-compliant?

int32_t c[3][2] = { { 1, 2 }, { 3, 4 } };


What about the arrays below, are they compliant or not, and why? Also, are they violatin 9.2 or 9.4?
int32_t d[1][2] = { [0][1]=2, [0]={1} };
int32_t e[1][2] = { [0]={1}, [0][1]=2 };
int32_t f[3][2] = { [1]={3, 4}, { 5, 6 }, [0][1]=2, [0][0]=1 };
int32_t g[2][2] = { { 1, 2 }, [1][0]=3, 4 };

Let me know what you think. If you have more (tricky) examples, then please share!

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