C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Prevent objects being passed to sprintf?          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message jf Guest Posted: Thu Dec 08, 2005 12:47 pm    Post subject: Prevent objects being passed to sprintf? Is there anything I can do in a class implementation to stop people from passing an object of that class to sprintf in it's variable argument list? A compile warning would be better than nothing, but passing objects in a variable parameter list just seems to bypass any type checking. If I could just force an overloaded operator to be called, for example. I know we shouldn't be using sprintf anymore, but in practice it does get used occasionally. Thanks, JF [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Ron Natalie Guest Posted: Thu Dec 08, 2005 4:16 pm    Post subject: Re: Prevent objects being passed to sprintf? jf wrote: Quote: Is there anything I can do in a class implementation to stop people from passing an object of that class to sprintf in it's variable argument list? No, unfortunately not. It would be nice if there was an operator... to allow you to either prohibit this or to provide a conversion to some type that is legal for vararg'd functions, but it doesn't exist. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Pete Becker Guest Posted: Thu Dec 08, 2005 6:19 pm    Post subject: Re: Prevent objects being passed to sprintf? jf wrote: Quote: Is there anything I can do in a class implementation to stop people from passing an object of that class to sprintf in it's variable argument list? Remove its copy constructor. Personally, this is on my list of things not to worry about. -- Pete Becker Dinkumware, Ltd. (http://www.dinkumware.com) [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Hrayr BABAJANYAN Guest Posted: Thu Dec 08, 2005 8:13 pm    Post subject: Re: Prevent objects being passed to sprintf? Hi! The '...' (ellipsis) is not an operator, so it cannot be overloaded. The only operator that can be overloaded in this case is the ',' (comma) operator, one can make it in a way to produce a warning, but this will affect not only the sprintf call... So this solution is pretty silly... :) I think the use of ellipsis destroys all the type checking stuff. So there is no way do what you want. Cheers! [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Rob Guest Posted: Thu Dec 08, 2005 11:47 pm    Post subject: Re: Prevent objects being passed to sprintf? Pete Becker wrote: Quote: jf wrote: Is there anything I can do in a class implementation to stop people from passing an object of that class to sprintf in it's variable argument list? Remove its copy constructor. I'm not sure if that is actually a solution to the probkem. Unfortunately, even if it is, it has a few additional side-effects that may be undesirable ..... Quote: Personally, this is on my list of things not to worry about. I agree. If someone is passing an object to sprintf(), there are almost certainly other problems in their code which will be much more significant. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Dietmar Kuehl Guest Posted: Fri Dec 09, 2005 10:50 am    Post subject: Re: Prevent objects being passed to sprintf? Hrayr BABAJANYAN wrote: Quote: The only operator that can be overloaded in this case is the ',' (comma) operator, .... and even this wouldn't help: the comma operator is not considered were it could be confused with the comma separating function arguments. -- <mailto:dietmar_kuehl (AT) yahoo (DOT) com> <http://www.dietmar-kuehl.de/> <http://www.eai-systems.com> - Efficient Artificial Intelligence [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Rob Guest Posted: Fri Dec 09, 2005 10:58 am    Post subject: Re: Prevent objects being passed to sprintf? Pete Becker wrote: Quote: jf wrote: Is there anything I can do in a class implementation to stop people from passing an object of that class to sprintf in it's variable argument list? Remove its copy constructor. I'm not sure if that is actually a solution to the probkem. Unfortunately, even if it is, it has a few additional side-effects that may be undesirable ..... Quote: Personally, this is on my list of things not to worry about. I agree. If someone is passing an object to sprintf(), there are almost certainly other problems in their code which will be much more significant. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top jf Guest Posted: Fri Dec 09, 2005 11:01 am    Post subject: Re: Prevent objects being passed to sprintf? In article <4398ae25 (AT) duster (DOT) adelaide.on.net>, [email]nospam (AT) nonexistant (DOT) com[/email] (Rob) wrote: Quote: I agree. If someone is passing an object to sprintf(), there are almost certainly other problems in their code which will be much more significant. Sometimes it can be just a typo, passing a string instead of the return from it's c_str() method. Especially when integrating with older code. It's very irritating that in such a type safe environment, this can slip through without even a compiler warning. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top antonmuhin Guest Posted: Fri Dec 09, 2005 3:15 pm    Post subject: Re: Prevent objects being passed to sprintf? I'm not sure that it might be finished as an expected solution, but maybe something along this lines will do (especially, if you don't use sprintf often). Redefine sprintf as a macro to your own function. As was pointed out one cannot control vargs function, but you can produce enougth number of overloads to match all the cases (and maybe add vargs overload to produce compile time warning, if used). These overloads can be shaped as below: template int mySprintf(char const * fmt, T1 p1, T2) { compile-time check for T1 --- quite easy with template magic compile-time check for T2 call to old sprintf } Of course, you might want a script to generate these overloads. hth, anton. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze Guest Posted: Fri Dec 09, 2005 3:59 pm    Post subject: Re: Prevent objects being passed to sprintf? jf wrote: Quote: Is there anything I can do in a class implementation to stop people from passing an object of that class to sprintf in it's variable argument list? If by object, you mean an object of class type, I don't understand the problem. According to the standard, "if the argument has a non-POD class type, the behvior is undefined.", and I don't think I've ever seen a compiler which didn't generate a warning (although I'll admit, it's not something that I verify very often). Quote: A compile warning would be better than nothing, but passing objects in a variable parameter list just seems to bypass any type checking. If I could just force an overloaded operator to be called, for example. I know we shouldn't be using sprintf anymore, but in practice it does get used occasionally. In practice, you probably never should have been using sprintf. Like all functions which write to a buffer without being passed the buffer's length, it is an invitation to buffer overrun problems. In the case of sprintf, there are ways of avoiding them, but they are all so complicated that it isn't worth the bother. -- James Kanze GABI Software Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, 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! ] Back to top Paavo Helde Guest Posted: Sat Dec 10, 2005 12:54 pm    Post subject: Re: Prevent objects being passed to sprintf? [email]hotmail (AT) hotmail (DOT) com[/email] (jf) wrote in news:memo.20051209093842.2864A (AT) crabtree (DOT) gmail.com: Quote: Sometimes it can be just a typo, passing a string instead of the return from it's c_str() method. Especially when integrating with older code. It's very irritating that in such a type safe environment, this can slip through without even a compiler warning. So couldn't you just compile your code with g++ -Wall? Even if you are not targeting Linux, this might be a good catch for this and possibly for other errors as well. hth Paavo [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top jf Guest Posted: Mon Dec 12, 2005 4:54 pm    Post subject: Re: Prevent objects being passed to sprintf? In article <Xns97281743D8782paavo256 (AT) 194 (DOT) 126.101.124>, [email]nobody (AT) ebi (DOT) ee[/email] (Paavo Helde) wrote: Quote: So couldn't you just compile your code with g++ -Wall? Even if you are not targeting Linux, this might be a good catch for this and possibly for other errors as well. I'm sure we could use some other tool (g++ in this case) to detect these types of problems, but I was after something that I could do in class design to avoid the problem in the first place. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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