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Full Version: Dir 4.8 if struct is only visible through a function declaration
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Hi there,
I humbly ask for help with compliance to Dir 4.8.
(Borrowing from cxlin, thx)
/* 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?
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.
The following discussion assumes that the prototype for usetype is
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.
/* 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.