Addressing only standards compliance, the C99 (n1256) standard says as follows.
7.21.1 /2 Where an argument declared as size_t n specifies the length of the array for a function, n can have the value zero on a call to that function. Unless explicitly stated otherwise in the description of a particular function in this subclause, pointer arguments on such a call shall still have valid values, as described in 7.1.4. On such a call, a function that locates a character finds no occurrence, a function that compares two character sequences returns zero, and a function that copies characters copies zero characters. Later versions of the standard contain similar wording. A zero value for the third argument of memset() is standards compliant. Any warning by any compiler is for the convenience of developers and may be safely disabled or ignored while remaining standards compliant. In my opinion, disabling or simply ignoring the warning are both legitimate choices. Modifying the code to suppress the warning is NOT. Regards David M Bennett FACS Andl - A New Database Language - andl.org -----Original Message----- From: sqlite-users-boun...@mailinglists.sqlite.org [mailto:sqlite-users-bounces at mailinglists.sqlite.org] On Behalf Of Scott Robison Sent: Friday, 21 August 2015 3:05 AM To: General Discussion of SQLite Database <sqlite-users at mailinglists.sqlite.org> Subject: Re: [sqlite] Compile warnings On Thu, Aug 20, 2015 at 10:46 AM, Scott Doctor <scott at scottdoctor.com> wrote: > My opinion is to keep it portable. The warning is there for a reason. > you are worried about performance yet are calling a function that does > nothing, which will take more memory cycles than a simple check for zero. > I didn't say don't make a change. I'm observing there are things to consider. In particular the optimization strategies that the SQLite team have pursued for several years now have been *tiny* little optimizations that would never be justifiable on their own but that really add up, particularly for small devices probably running on batteries. > Trying to memset a zero length is a bug, not the warning. Add an if > statement around it. If the variable is local, it will probably be > optimized as a register variable and a zero check of a register is a > single op-code. > Trying to memset a zero length buffer is not a bug if the length of the sequence of bytes that needs to be set is zero. C89 in particular does not disallow this use. > the problem with disabling warnings is that even if this instance is > not an error, some other part of the code may end up with the same > situation but is an error in the coding. I would prefer code that can > be compiled with all warnings turned on that gives no warnings than > have a potential problem because of a glitch in the code. > I don't think anyone called for disabling the warning. I think it should just be ignored in this case, just as I ignore warnings that are generated by Visual C++ when I compile SQLite there. -- Scott Robison _______________________________________________ sqlite-users mailing list sqlite-users at mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
