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+---- Forum: 6.11 Pointer Type Conversions (https://forum.misra.org.uk/forumdisplay.php?fid=38)
+---- Thread: Double casting to bypass 11.4? (/showthread.php?tid=676)
Double casting to bypass 11.4? - exoson - 04-09-2009
I ran into an issue with a static analysis tool the other day.
In my example:
pool_ptr->list = *((UCHAR **) work_ptr); /*violates MISRA 11.4 */
Both pointers are UCHAR *. The first location in the buffer is being used to hold another pointer.
Adding an intermediate cast to void * clears the warning.
pool_ptr -> tx_list = *((UCHAR **) (void *)work_ptr);
Regardless that this clears the message, I believe it is still a violation of the intent of MISRA 11.4. Do you agree?
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Scott Nowell
Validated Software Corporation
Re: Double casting to bypass 11.4? - William Forbes - 05-09-2009
Rule 11.4 uses the word "cast" when in reality the problem is the conversion (and the subsequent dereferencing).
Maybe Rule 11.4 could read:
The value of a pointer to an object type shall not be assigned the value of a pointer to an object of a different type.
William Forbes
Re: Double casting to bypass 11.4? - William Forbes - 07-09-2009
Does anybody have any comments on the following (as far as I can tell) MISRA compliant code:
Code:
uint8_t u8 = 0U ;
uint8_t * ptr_u8 = &u8 ;
void * ptr_nothing = ptr_u8 ; /* Rule 11.2 compliant */
uint16_t * ptr_u16 = ptr_nothing ; /* Rule 11.4 compliant - no cast */
uint16_t u16 = *ptr_u16 ; /* What value is u16 ? !! */I think the 0 is missing from the definition of a null pointer constant, unless it is talking about a pointer to void!
Bill Forbes
Re: Double casting to bypass 11.4? - misra-c - 09-09-2009
Conversion of a pointer to object to a pointer to different object via a pointer to void is permitted by the MISRA C rules. While this style of coding is questionable, the MISRA C Working Group felt unable to prevent it given the extensive use of pointers to void in the C library.
We acknowledge the typographical error in the 2nd paragraph of 6.11. It should indeed have said (void *)0.
Tracker Id: 41