C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  pointer to type_info          C++Talk.NET Forum Index -> C++ language, library and standards View previous topic :: View next topic   Author Message John Torjo Guest Posted: Tue Jul 20, 2004 6:03 am    Post subject: pointer to type_info Hi, Heres's what the standard says: [expr.typeid] 5.2.8 Type identification The result of a typeid expression is an lvalue of static type const std::type_info (18.5.1) and dynamic type const std::type_info or const name where name is an implementation defined class derived from std::type_info which preserves the behavior described in 18.5.1. The lifetimeof the object referred to by the lvalue extends to the end of the program. Whether or not the destructor is called for the type_info object at the end of the program is unspecified. Quick question: If I read this correctly, I can hold a pointer to dereferencing a typeid(), and that pointer will last throughout the program. Am I correct? Example: some_class * p = ...; // this will last throughout the program const std::type_info * info = &typeid(*p); Thanks. Best, John John Torjo Freelancer -- [email]john (AT) torjo (DOT) com[/email] Contributing editor, C/C++ Users Journal -- "Win32 GUI Generics" -- generics & GUI do mix, after all -- http://www.torjo.com/win32gui/ Professional Logging Solution for FREE -- http://www.torjo.com/code/logging.zip (logging - C++) -- http://www.torjo.com/logview/ (viewing/filtering - Win32) -- http://www.torjo.com/logbreak/ (debugging - Win32) (source code available) --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top James Kuyper Guest Posted: Sat Jul 24, 2004 5:23 am    Post subject: Re: pointer to type_info [email]jtorjo (AT) yahoo (DOT) com[/email] (John Torjo) wrote in message news:<c638aac5.0407191103.708c6bfd (AT) posting (DOT) google.com>... ... Quote: If I read this correctly, I can hold a pointer to dereferencing a typeid(), and that pointer will last throughout the program. Am I correct? Example: some_class * p = ...; // this will last throughout the program const std::type_info * info = &typeid(*p); I think that what you meant to say is correct, but that you haven't worded it correctly. You're taking the address of typeid, not dereferencing it. How long the pointer would last depends upon how it's defined; assuming that it has static storage duration that's essentially the same as the length of the program. However, I suspect that you're not really interested in how long the pointer lasts; you're interested in how long it remains useable. It is indeed useable from the moment you assign it that value, until the end of the program. --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top John Torjo Guest Posted: Mon Jul 26, 2004 5:03 pm    Post subject: Re: pointer to type_info [email]kuyper (AT) wizard (DOT) net[/email] (James Kuyper) wrote in message news:<8b42afac.0407231931.219f8a0d (AT) posting (DOT) google.com>... Quote: jtorjo (AT) yahoo (DOT) com (John Torjo) wrote in message news:<c638aac5.0407191103.708c6bfd (AT) posting (DOT) google.com>... .. If I read this correctly, I can hold a pointer to dereferencing a typeid(), and that pointer will last throughout the program. Am I correct? Example: some_class * p = ...; // this will last throughout the program const std::type_info * info = &typeid(*p); I think that what you meant to say is correct, but that you haven't worded it correctly. You're taking the address of typeid, not dereferencing it. How long the pointer would last depends upon how it's defined; assuming that it has static storage duration that's essentially the same as the length of the program. However, I suspect that you're not really interested in how long the pointer lasts; you're interested in how long it remains useable. It is indeed useable from the moment you assign it that value, until the end of the program. I assume I think that the pointer is useable as long as it lasts ;) Anyway, internally I need a map that is sorted by std::type_info. So that I can create a templated function, and see if it's been called before for the same type. Best, John John Torjo Freelancer -- [email]john (AT) torjo (DOT) com[/email] Contributing editor, C/C++ Users Journal -- "Win32 GUI Generics" -- generics & GUI do mix, after all -- http://www.torjo.com/win32gui/ Professional Logging Solution for FREE -- http://www.torjo.com/code/logging.zip (logging - C++) -- http://www.torjo.com/logview/ (viewing/filtering - Win32) -- http://www.torjo.com/logbreak/ (debugging - Win32) (source code available) --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. 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