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+---- Thread: Why rule 18.1? (/showthread.php?tid=629)
Why rule 18.1? - exoson - 19-02-2009
Please help me understand the reason for rule 18.1. In the context of an "opaque pointer", one can properly make and use such a pointer to an incompletely typed structure. Having the full structure declaration is not needed. The committee has endorsed this in a previous post.
What coding practice is left that might cause a problem? If the type is incomplete, a compile error will result from any attempt to create an object of that type or refer to its members.
OK, but even so, why not require it? In header files, I like to code:
struct something; /* with a forward declaration, I can create pointers. */
void foo (struct something *pointerToSomething);
The prototype is valid even though "something" is of incomplete type. If the #including .c file does not need anything other than the pointer, why require #including yet another header merely to get the (unused) full declaration and satisfy the rule?
Re: Why rule 18.1? - misra-c - 12-03-2009
MISRA acknowledges that opaque types should be allowed and has changed Rule 18.1 to permit their use. Full details of this change are given in "MISRA-C:2004 Technical Corrigendum 1", which can be downloaded from the Resources / MISRA C resources area of the forum (registered users only).