C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Type and value of basic_string::npos          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Heinz Ozwirk Guest Posted: Sat Oct 29, 2005 7:14 am    Post subject: Type and value of basic_string::npos Does the standard require that 1. the type of basic_string::npos is an unsigned type? 2. the value of basic_string::npos is the largest possible value of that type? And - only if both are true - basic_string::npos + 1 == 0 ? Tnx Heinz Back to top John Harrison Guest Posted: Sat Oct 29, 2005 7:19 am    Post subject: Re: Type and value of basic_string::npos Heinz Ozwirk wrote: Quote: Does the standard require that 1. the type of basic_string::npos is an unsigned type? 2. the value of basic_string::npos is the largest possible value of that type? And - only if both are true - basic_string::npos + 1 == 0 ? Tnx Heinz Yes, yes and yes. john Back to top Jonathan Mcdougall Guest Posted: Sat Oct 29, 2005 7:22 am    Post subject: Re: Type and value of basic_string::npos Heinz Ozwirk wrote: Quote: Does the standard require that 1. the type of basic_string::npos is an unsigned type? Yes. Quote: 2. the value of basic_string::npos is the largest possible value of that type? Yes. It is actually required to be -1. Quote: And - only if both are true - basic_string::npos + 1 == 0 ? Yes. However, npos is required to be an unsigned *integral*, no more. Be careful to use only values of type basic_string::size_type when you compare them to npos. A comparison with an unsigned int (or whatever other type) is not portable. Jonathan Back to top Ivan Vecerina Guest Posted: Sat Oct 29, 2005 2:15 pm    Post subject: Re: Type and value of basic_string::npos "Heinz Ozwirk" <hozwirk.SPAM (AT) arcor (DOT) de> wrote : Does the standard require that : : 1. the type of basic_string::npos is an unsigned type? Yes. : 2. the value of basic_string::npos is the largest possible value of that : type? Yes. : And - only if both are true - basic_string::npos + 1 == 0 ? Not necessarily, as far as I understand. If basic_string::npos is of type 'unsigned short' (16 bits), and int is 32 bits, then npos+1 would be promoted to a (32-bit) int, and the result would be: 65536 The following however shall always be true: ~basic_string::npos == 0 Ivan -- http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form Brainbench MVP for C++ <> http://www.brainbench.com Back to top Pete Becker Guest Posted: Sat Oct 29, 2005 2:26 pm    Post subject: Re: Type and value of basic_string::npos Ivan Vecerina wrote: Quote: If basic_string::npos is of type 'unsigned short' (16 bits), and int is 32 bits, then npos+1 would be promoted to a (32-bit) int, and the result would be: 65536 That's the right answer, but you've got the promotion in the wrong place. Since 1 is of type int and npos is of type unsigned short (in this example), npos will be promoted to int. Once that promotion has been done, the sum has type int. -- Pete Becker Dinkumware, Ltd. (http://www.dinkumware.com) Back to top Valentin Samko Guest Posted: Sat Oct 29, 2005 3:34 pm    Post subject: Re: Type and value of basic_string::npos Pete Becker wrote: Quote: Ivan Vecerina wrote: If basic_string::npos is of type 'unsigned short' (16 bits), and int is 32 bits, then npos+1 would be promoted to a (32-bit) int, and the result would be: 65536 That's the right answer, but you've got the promotion in the wrong place. Since 1 is of type int and npos is of type unsigned short (in this example), npos will be promoted to int. Once that promotion has been done, the sum has type int. But still, when unsigned 16bit integer which was assigned -1 is promoted to int, we get 65535 in that int. And then we add 1 to that, getting 65536. typedef unsigned short ushort; std::cout<<(ushort(-1) + 1)< outputs 65536 on vc7.1, g++ 3.4 and intel 9, as I expected. -- Valentin Samko - http://www.valentinsamko.com Back to top Pete Becker Guest Posted: Sat Oct 29, 2005 5:14 pm    Post subject: Re: Type and value of basic_string::npos Valentin Samko wrote: Quote: Pete Becker wrote: Ivan Vecerina wrote: If basic_string::npos is of type 'unsigned short' (16 bits), and int is 32 bits, then npos+1 would be promoted to a (32-bit) int, and the result would be: 65536 That's the right answer, but you've got the promotion in the wrong place. Since 1 is of type int and npos is of type unsigned short (in this example), npos will be promoted to int. Once that promotion has been done, the sum has type int. But still, when unsigned 16bit integer which was assigned -1 is promoted to int, we get 65535 in that int. And then we add 1 to that, getting 65536. Yes, that's what "That's the right answer" means. -- Pete Becker Dinkumware, Ltd. (http://www.dinkumware.com) Back to top Ivan Vecerina Guest Posted: Sun Oct 30, 2005 4:50 am    Post subject: Re: Type and value of basic_string::npos "Valentin Samko" <c++.moderated (AT) digiways (DOT) com> wrote : Pete Becker wrote: : > Ivan Vecerina wrote: : >> If basic_string::npos is of type 'unsigned short' (16 bits), : >> and int is 32 bits, then npos+1 would be promoted to : >> a (32-bit) int, and the result would be: 65536 : >> : > : > That's the right answer, but you've got the promotion in the wrong : > place. Since 1 is of type int and npos is of type unsigned short (in : > this example), npos will be promoted to int. Once that promotion has : > been done, the sum has type int. : : But still, when unsigned 16bit integer which was assigned -1 : is promoted to int, we get : 65535 in that int. And then we add 1 to that, getting 65536. : : typedef unsigned short ushort; : std::cout<<(ushort(-1) + 1)< : : outputs 65536 on vc7.1, g++ 3.4 and intel 9, as I expected. Yes. What Pete's point was is that the following statement I made was inaccurate: << npos+1 would be promoted to a (32-bit) int >> It is 'npos' itself that is first promoted to an int *prior* to adding the integer value '1'. Lack of clarity on my side -- pointed out by Pete in his personal style that often makes it sound like everything previously said is 'crap'. Cheers, Ivan -- http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ language (comp.lang.c++) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.