localtime deprecated?
in [C++]
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From: Martin Bonner on 3 Jun 2006 10:03 lists(a)givemefish.com wrote: > Hi all, > > while compiling an existing project in the new MSVC 2005 compiler, I > received the warning that: > > : warning C4996: 'localtime' was declared deprecated > C:\Program Files\Microsoft Visual Studio > 8\VC\include\time.inl(114) : see declaration of 'localtime' > Message: 'This function or variable may be unsafe. Consider > using localtime_s instead. To disable deprecation, use > _CRT_SECURE_NO_DEPRECATE. See online help for details.' > > > I wasn't aware that localtime was declared deprecated. Is this true? Yes. You can see the declaration in the error message. The question you haven't asked is WHO declared it deprecated. The answer is Microsoft (because if used carelessly, localtime can overflow a buffer). > > And, if so, is the suggestion of localtime_s standard compliant? No. > If not, what should I use? [This program has to be > platform-independent, ISO C++.] In that case, you should use localtime (and you probably want to disable the warning). Of course if you are stuck in one of those foolish shops that /also/ say "code must compile warning free with all warnings enabled", you are a bit stuck! [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Jake Montgomery on 3 Jun 2006 20:35 On 6/3/2006 4:53 AM, kanze wrote: > lists(a)givemefish.com wrote: > >>while compiling an existing project in the new MSVC 2005 >>compiler, I received the warning that: > > >>: warning C4996: 'localtime' was declared deprecated >> >>I wasn't aware that localtime was declared deprecated. Is >>this true? > > > Not by the C++ committee, nor by the C committee (I think). > Maybe by Microsoft. In fact, the message is misleading; I think > Microsoft has admitted this, and plans to change it in the next > release. > > On the other hand, there are cases where localetime might be > unsafe -- it cannot be used in multithreaded code, for example. > And this fact was recognized and addressed by the C committee. > Except for the word "deprecated" itself, the Microsoft warning > pretty much corresponds to what the C committee has said. > Could you explain why localtime is considered to be inherently unsafe for multithreading? It would seem that its thread safety would be implementation dependent ... especially since AFAIK the C++ standard does not address threading at all. It would seem that the tm structure returned would be "per-thread" in any self respecting mutlithreaded standard C++ library. Is that a naive assumption, or am I missing something else in the definition that makes it inherently unsafe? Curious, Jake Montgomery [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: James Kanze on 3 Jun 2006 20:41 Martin Bonner wrote: > lists(a)givemefish.com wrote: >> while compiling an existing project in the new MSVC 2005 >> compiler, I received the warning that: >> : warning C4996: 'localtime' was declared deprecated >> C:\Program Files\Microsoft Visual Studio >> 8\VC\include\time.inl(114) : see declaration of 'localtime' >> Message: 'This function or variable may be unsafe. Consider >> using localtime_s instead. To disable deprecation, use >> _CRT_SECURE_NO_DEPRECATE. See online help for details.' >> I wasn't aware that localtime was declared deprecated. Is >> this true? > Yes. You can see the declaration in the error message. The > question you haven't asked is WHO declared it deprecated. The > answer is Microsoft (because if used carelessly, localtime can > overflow a buffer). Can it? I don't think so. On the other hand, there is no way to use it at all in a multithreaded environment. Which raises an interesting question: if C++ adopts threading as part of the language, do we also adopt this TR? Or? -- James Kanze kanze.james(a)neuf.fr Conseils en informatique orient?e objet/ Beratung in objektorientierter Datenverarbeitung 9 place S?mard, 78210 St.-Cyr-l'?cole, France +33 (0)1 30 23 00 34 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: James Kanze on 4 Jun 2006 09:18 Jake Montgomery wrote: [...] > Could you explain why localtime is considered to be inherently > unsafe for multithreading? Read the specification. I suppose it could be made thread safe by using some sort of thread local storage, but in general, the wording of the standard encourages the use of static data. > It would seem that its thread safety would be implementation > dependent ... especially since AFAIK the C++ standard does not > address threading at all. The fact that the standard doesn't address threading at all means that you have undefined behavior as soon as there is more than one thread. > It would seem that the tm structure returned would be > "per-thread" in any self respecting mutlithreaded standard C++ > library. Well, it's definitely not the case in Posix, which introduced localtime_r to avoid the problem. It might be the case in some Windows libraries, however; I'm not sure. > Is that a naive assumption, or am I missing something else in > the definition that makes it inherently unsafe? I think it's a naive assumption, although I can see where it makes sense. In practice, early threading systems, at least on Unix systems, didn't have any direct support for thread local storage, and emulating it was felt to be too expensive, and possibly to introduce memory leaks -- you allocate the thread local memory the first time the function is called within a given thread, but when do you free it? -- James Kanze kanze.james(a)neuf.fr Conseils en informatique orient?e objet/ Beratung in objektorientierter Datenverarbeitung 9 place S?mard, 78210 St.-Cyr-l'?cole, France +33 (0)1 30 23 00 34 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Robert Kindred on 5 Jun 2006 13:53
"Victor Bazarov" <v.Abazarov(a)comAcast.net> wrote in message news:e5mogb$udv$1(a)news.datemas.de... > lists(a)givemefish.com wrote: [] >> And, if so, is the suggestion of localtime_s standard compliant? > > No. > >> If not, what should I use? [This program has to be >> platform-independent, ISO C++.] > > Keep using 'localtime' until MS comes to its senses (unlikely) or > until MS removes it completely from its library implementation (also > unlikely). When/If the latter happens, split the code using an ifdef > directive. I am afraid "remove completely" is not so far fetched. I prefer to use opendir and readdir to scan directories for a modicum of platform independence. This worked in Borland Builder5, but it is gone from Microsoft VS2005. Robert Kindred [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] |