MISRA Discussion Forums
Dir 4.8 if struct is only visible through a function declaration - Printable Version

+- MISRA Discussion Forums (https://forum.misra.org.uk)
+-- Forum: MISRA C (https://forum.misra.org.uk/forumdisplay.php?fid=4)
+--- Forum: MISRA C:2012 and MISRA C:2023 guidelines (https://forum.misra.org.uk/forumdisplay.php?fid=21)
+---- Forum: 7.4 Code design (https://forum.misra.org.uk/forumdisplay.php?fid=181)
+---- Thread: Dir 4.8 if struct is only visible through a function declaration (/showthread.php?tid=1452)

Dir 4.8 if struct is only visible through a function declaration - LMende - 29-08-2018

Hi there,
I humbly ask for help with compliance to Dir 4.8.
(Borrowing from cxlin, thx)
Code:
/* def.h */
struct SomeType
{
/* Object implementation */
}

/* other.h */
extern void usetype(someType* p);

/* no-use.c */
#include def.h
#include other.h
/* Do something. But no use of SomeType at all. */
Given a structure SomeType which implementation is visible to no-use.c.
A pointer to SomeType is only visible through the included other.h where the usetype function is declared.
Is the implementation of no-use.c compliant with Dir 4.8 or not?

Re: Dir 4.8 if struct is only visible through a function declaration - dg1980 - 30-08-2018

First let me quote MISRA C 2012 chapter 6.1:
Quote:A directive is a guideline for which it is not possible to provide the full description necessary to perform a check for compliance

Also, it is classified advisory, so it would not require a formal deviation.

The answer to your question depends on whether other translation units in your project include def.h and use struct SomeType directly (creating a variable, accessing members etc.).
In that case, the opaque technique described in DIR 4.8 does not apply.

Re: Dir 4.8 if struct is only visible through a function declaration - misra-c - 16-10-2018

The following discussion assumes that the prototype for usetype is
Code:
extern void usetype(struct SomeType* p);

The translation unit for no-use.c never accesses the members of "struct SomeType" and therefore the example is not compliant with directive 4.8. To be compliant with this rule another header file should be created.
Code:
/* opaque_def.h */
typedef struct SomeType *pSomeType;

/* other.h */
extern void usetype(pSomeType p);

/* no-use.c */
#include opaque_def.h
#include other.h
/* Do something. But no use of SomeType at all. */
opaque_def.h would be used in those translation units which did not dereference the pointer "struct SomeType *" whereas def.h would be used in those translation units which did dereference the pointer.
Whether a particular translation unit violates directive 4.8 does not depend on how "struct SomeType" is used in other translation units.