A NOTE has been added to this issue. ====================================================================== https://austingroupbugs.net/view.php?id=1647 ====================================================================== Reported By: eblake Assigned To: ====================================================================== Project: 1003.1(2016/18)/Issue7+TC2 Issue ID: 1647 Category: System Interfaces Type: Clarification Requested Severity: Objection Priority: normal Status: Interpretation Required Name: Eric Blake Organization: Red Hat User Reference: ebb.printf %lc Section: fprintf Page Number: 913 Line Number: 30957 Interp Status: Proposed Final Accepted Text: https://austingroupbugs.net/view.php?id=1647#c6239 ====================================================================== Date Submitted: 2023-03-28 16:32 UTC Last Modified: 2023-06-29 11:28 UTC ====================================================================== Summary: printf("%lc", (wint_t)0) can't output NUL byte ====================================================================== Relationships ID Summary ---------------------------------------------------------------------- related to 0001643 fprintf %lc: wrong reference to the cur... ======================================================================
---------------------------------------------------------------------- (0006369) geoffclare (manager) - 2023-06-29 11:28 https://austingroupbugs.net/view.php?id=1647#c6369 ---------------------------------------------------------------------- > As it turns out, there is one other place that does say this is what is intended: the description of CX "Extension to the ISO C standard" The CX text is just giving information about statements that exist on other pages. But thanks for pointing it out, because that text no longer matches the statements it is referring to, and so needs adjusting. > I understand from your comments that your view is that when _POSIX_C_SOURCE/_XOPEN_SOURCE is not defined, rather than deferring to ISO C, the behaviour is undefined (unspecified?) in POSIX. [...] Is that a correct interpretation of your comments? Yes, it's undefined. Anywhere POSIX requires confirming applications to do something (such as the numerous places it says "The application shall ensure that ..."), if an application doesn't do that thing then the behaviour is undefined. I see no reason that this would not include the requirement to define _POSIX_C_SOURCE or _XOPEN_SOURCE. > If it is, the whole "Extension to the ISO C standard" is silly: there cannot be even a single program that is both valid under ISO C and valid under POSIX under your interpretation that includes any standard library headers: if _POSIX_C_SOURCE/_XOPEN_SOURCE are defined, the behaviour is undefined under ISO C, if _POSIX_C_SOURCE/_XOPEN_SOURCE are not defined, the behaviour is undefined under POSIX. That does not extend ISO C in any meaningful way. It just means that conforming to ISO C and conforming to POSIX are two independent choices that implementations can make. <b>If</b> an implementation chooses to conform to both, then there will indeed be many programs that are both valid under ISO C and valid under POSIX, and on such implementations POSIX extends C. But implementations ought to be able to choose to just support POSIX and not "bare C" if they want to. > ISO C does not require the use of standard library headers True, which means an implementation that wants to support both printf() behaviours would not be able to choose between them based on whether _POSIX_C_SOURCE/_XOPEN_SOURCE is defined. But there are other ways they could do it (command line options and environment variables being the most obvious). > Note that if WG14 would be willing to classify this as a defect, that avoids the entire issue. That is indeed the root cause of this entire issue. WG14 are not issuing DRs for C17, so we are forced to address C17 defects by saying that POSIX does not defer to C17 for certain specific things. I expect that in practice, implementations will treat the change in C23 as being a de-facto DR for C17 and act accordingly. Issue History Date Modified Username Field Change ====================================================================== 2023-03-28 16:32 eblake New Issue 2023-03-28 16:32 eblake Name => Eric Blake 2023-03-28 16:32 eblake Organization => Red Hat 2023-03-28 16:32 eblake User Reference => ebb.printf %lc 2023-03-28 16:32 eblake Section => fprintf 2023-03-28 16:32 eblake Page Number => 913 2023-03-28 16:32 eblake Line Number => 30957 2023-03-28 16:32 eblake Interp Status => --- 2023-03-28 16:32 eblake Relationship added child of 0001643 2023-03-28 16:33 eblake Desired Action Updated 2023-03-28 17:02 eblake Desired Action Updated 2023-03-28 17:30 eblake Note Added: 0006237 2023-03-28 17:31 eblake Description Updated 2023-03-28 17:37 eblake Desired Action Updated 2023-03-30 16:33 eblake Note Added: 0006239 2023-03-30 17:14 eblake Tag Attached: tc3-2008 2023-03-30 17:14 eblake Tag Attached: issue8 2023-04-03 15:27 eblake Note Added: 0006246 2023-04-03 15:28 eblake Note Edited: 0006239 2023-04-03 15:28 geoffclare Tag Detached: tc3-2008 2023-04-03 15:31 ajosey Interp Status --- => Pending 2023-04-03 15:31 ajosey Final Accepted Text => https://austingroupbugs.net/view.php?id=1647#c6239 2023-04-03 15:31 ajosey Resolution Open => Accepted As Marked 2023-04-03 15:32 ajosey Status New => Interpretation Required 2023-04-03 16:31 ajosey Note Added: 0006248 2023-04-03 16:31 ajosey Status Interpretation Required => Resolution Proposed 2023-04-03 16:46 hvd Note Added: 0006251 2023-04-03 17:15 ajosey Interp Status Pending => Proposed 2023-04-03 17:15 ajosey Status Resolution Proposed => Interpretation Required 2023-04-20 16:22 geoffclare Relationship replaced related to 0001643 2023-06-23 16:19 geoffclare Note Added: 0006346 2023-06-23 16:45 hvd Note Added: 0006347 2023-06-26 09:25 geoffclare Note Added: 0006349 2023-06-26 09:56 hvd Note Added: 0006350 2023-06-27 08:58 geoffclare Note Added: 0006361 2023-06-27 12:29 geoffclare Note Added: 0006365 2023-06-29 01:47 hvd Note Added: 0006366 2023-06-29 02:01 hvd Note Edited: 0006366 2023-06-29 11:28 geoffclare Note Added: 0006369 ======================================================================
