C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Unions to avoid strong C++ type checking          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message mdlinux7@yahoo.co.in Guest Posted: Wed Oct 19, 2005 8:42 am    Post subject: Unions to avoid strong C++ type checking Hi All, Can anyone give me a pratical examples where unions can be used to avoid C++ type checking. Regards Dinesh [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Dan McLeran Guest Posted: Thu Oct 20, 2005 11:10 am    Post subject: Re: Unions to avoid strong C++ type checking Here's an example: http://www.cuj.com/documents/s=9360/cujexp0410wilson/ [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Allan W Guest Posted: Thu Oct 20, 2005 11:24 am    Post subject: Re: Unions to avoid strong C++ type checking Dinesh (mdlinux7 (AT) yahoo (DOT) co.in) wrote: Quote: Can anyone give me a pratical examples where unions can be used to avoid C++ type checking. I hope not. If you're trying to do this for one or two special cases, such as a database field, you should probably look at one of the classes in Boost, such as boost::any or boost::variant. See http://boost.org , http://boost.org/doc/html/any.html , and http://boost.org/doc/html/variant.html . If you're just trying to avoid specifying the types of your data fields -- C++ isn't the best language for that. C++ type checking exists for a reason, and if you fight it, you're going to get a program that's big and slow and difficult to maintain. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Gabriel Dos Reis Guest Posted: Thu Oct 20, 2005 11:27 am    Post subject: Re: Unions to avoid strong C++ type checking [email]mdlinux7 (AT) yahoo (DOT) co.in[/email] writes: Quote: Hi All, Can anyone give me a pratical examples where unions can be used to avoid C++ type checking. I'm interested in why you might want to do so. -- Gabriel Dos Reis [email]gdr (AT) integrable-solutions (DOT) net[/email] [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Carlos Moreno Guest Posted: Thu Oct 20, 2005 12:26 pm    Post subject: Re: Unions to avoid strong C++ type checking [email]mdlinux7 (AT) yahoo (DOT) co.in[/email] wrote: Quote: Hi All, Can anyone give me a pratical examples where unions can be used to avoid C++ type checking. I would actually be more curious about seeing an example where one would legitimately *want to avoid* C++ type checking... Carlos -- [ 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 Oct 21, 2005 4:15 pm    Post subject: Re: Unions to avoid strong C++ type checking Gabriel Dos Reis wrote: Quote: mdlinux7 (AT) yahoo (DOT) co.in writes: | Can anyone give me a pratical examples where unions can be | used to avoid C++ type checking. I'm interested in why you might want to do so. I can think of at least two cases where I did so in C: in the implementation of malloc/free/realloc in a C library, and in the implementation of ldexp/frexp/modf in the same library. Formally, my use was undefined behavior, according to the C standard. However 1) I wrote the code before there was a C standard, and I believe that Kernighan and Richie intended for unions to be usable this way, and 2) the code was anything but portable anyway, so I felt safe counting on my compiler guarantees. Still, today I'd use pointer casts to do the same thing. But in C++ terms, they'd be reinterpret_cast's, and not really any more portable than the union trick. Of course, this is very low level code. Not the sort of thing you'd be doing in a typical application. -- 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 Gabriel Dos Reis Guest Posted: Sat Oct 22, 2005 3:21 pm    Post subject: Re: Unions to avoid strong C++ type checking "kanze" <kanze (AT) gabi-soft (DOT) fr> writes: Quote: Gabriel Dos Reis wrote: [email]mdlinux7 (AT) yahoo (DOT) co.in[/email] writes: | Can anyone give me a pratical examples where unions can be | used to avoid C++ type checking. I'm interested in why you might want to do so. I can think of at least two cases where I did so in C: in the I was hoping "mdlinux7 (AT) yahoo (DOT) co.in" would clarify what he want to achieve with nontypeful programming in C++. -- Gabriel Dos Reis [email]gdr (AT) integrable-solutions (DOT) net[/email] [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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