From -1667602065283281409 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f635e,e7776fa3664990ff X-Google-Attributes: gidf635e,public X-Google-Thread: f78e5,5cc0e5689db82f7b X-Google-Attributes: gidf78e5,public From: hinnant@_anti-spam_lightlink.com (Howard Hinnant) Subject: Re: Is type_info object static or temporary? Date: 1998/06/02 Message-ID: #1/1 X-Deja-AN: 358633015 X-NNTP-Posting-Host: 205.232.34.144 Approved: stephen.clamage@sun.com (comp.std.c++) References: <356D82DA.36025D97@matfys.lth.se> <6kl3ar$npi$1@shell7.ba.best.com> <35727d32.0@210.134.196.10> X-UID: 0000000001 X-Status: $$$T Organization: Lightlink Internet Newsgroups: comp.std.c++,comp.sys.mac.programmer.codewarrior Originator: clamage@taumet In article <35727d32.0@210.134.196.10>, "HiroshiOda" wrote: > Why the class std::type_info is designed to be prevent copying? > I read 'The C++ programing language 3rd edi.'. And in section 15.4.4, RTTI > is described. I would like to use such a kind of map as map< type_info, ... > >, so I've first created the helper class as followings. > > class my_type_info { > private : > const type_info* info ; > public : > my_type_info() : info( 0 ) {} > my_type_info( const type_info& sorc ) : info( &sorc ) {} > my_type_info( const my_type_info& sorc ) : info( sorc.info ) {} > my_type_info& operator =( const my_type_info& sorc ) { info = sorc.info > ; > } > bool operator ==( const my_type_info& another ) { > return *info == *another.info ; > } > bool operator <( const my_type_info& another ) { > return info->before( *another.info ) ; > } > bool operator !=( ..... > bool operator >( ..... > ..... > } ; > > Now map< my_type_info, ... > is well-defined. But I'm not sure which we may > assume the return value of typeid() refers to something of temporary object > or global static object. If it is temporary object, the design of the class > my_type_info is bad. But Stroustrup's description of p.415 seems to say that > type_info objects are global objects. Can we assume so? No example there > bind the type_info object in any const references nor const pointers. > > Secondly, for safety I decide to design my map to be the form map< const > char*, ... > where const char* is a string pointer got by > typeid(...).name(). This is just as Stroustrup's example. Here I assume that > C-strings got by typeid(...).name() will never go. Again, can we assume so? > > Thanks to your help. I believe that your design is safe. The standard says: 1 The result of a typeid expression is an lvalue of static type const std::type_info (_lib.type.info_) 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 _lib.type.info_.9) The lifetime of the object referred to by the lvalue extends to the end of the program. Whether or not the destruc- tor is called for the type_info object at the end of the program is unspecified. The comment about the lifetime of the object, I believe, guarantees that info will always be pointing to a valid type_info (as long as it starts out that way). -Howard [ 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://reality.sgi.com/austern_mti/std-c++/faq.html ]