On Sep 23, 2009, at 5:31 PM, David-Sarah Hopwood <david-sa...@jacaranda.org > wrote:
> Jim Idle wrote: >> The following should be read carefully before upgrading to release >> 3.2 >> of the C target: > [...] >> * finally - this code is executed whether the rule parses >> successfully or not. This is probably where you should free >> allocations, but you should guard against uninitialized elements, >> which may not have been created on a parse error. > > Are such elements (not variables that you declare yourself) guaranteed > to be NULL? Yes, this is one of the issues of trying to use something other than pointers. > >> * Because you can end up executing both @after and finally code, >> use >> safe programming patterns (you should be anyway ;-, and assign >> NULL to anything after declaring it and immediately before >> freeing >> it. > > You mean immediately after freeing it :-) > (i.e. "free(foo); foo = NULL;") You know what I mean ;) > >> Also, guard against free(NULL) unless the semantics of your >> system specify that free(NULL) is allowed. > > "free(NULL)" is defined to be a no-op by the C standard. A libc > implementation that got this wrong would be badly broken, and AFAIK > all > the commonly used platforms get it right. Some platforms define this to be undefined though. Remember there are lots if embedded systems that use this. Hence the qualification. I think it would have been better to define free(NULL) as safe myself but early Lib C would crash if you did this and I think it was C++ that first took a stand? > > -- > David-Sarah Hopwood ⚥ http://davidsarah.livejournal.com > > > List: http://www.antlr.org/mailman/listinfo/antlr-interest > Unsubscribe: > http://www.antlr.org/mailman/options/antlr-interest/your-email-address List: http://www.antlr.org/mailman/listinfo/antlr-interest Unsubscribe: http://www.antlr.org/mailman/options/antlr-interest/your-email-address --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "il-antlr-interest" group. To post to this group, send email to il-antlr-interest@googlegroups.com To unsubscribe from this group, send email to il-antlr-interest+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/il-antlr-interest?hl=en -~----------~----~----~----~------~----~------~--~---
