exact difference between C style and static_cast, const_cast
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From: Brendan on 25 Feb 2010 15:57 O wise and powerful clcm, What's the precise difference between C style casts, and static_cast. I've always been told that static_cast and const_cast casts are better, but I'd like to know exactly in what circumstances they differ so I can make that judgement myself. Giving me a reference to something in the C++ standard is fine... Thanks, Brendan -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Seungbeom Kim on 25 Feb 2010 19:47 Brendan wrote: > O wise and powerful clcm, > > What's the precise difference between C style casts, and static_cast. > I've always been told that static_cast and const_cast casts are > better, but I'd like to know exactly in what circumstances they differ > so I can make that judgement myself. > > Giving me a reference to something in the C++ standard is fine... ISO/IEC 14882:2003, 5.4/5: The conversions performed by � a const_cast (5.2.11), � a static_cast (5.2.9), � a static_cast followed by a const_cast, � a reinterpret_cast (5.2.10), or � a reinterpret_cast followed by a const_cast, can be performed using the cast notation of explicit type conversion. [...] If a conversion can be interpreted in more than one of the ways listed above, the interpretation that appears first in the list is used, even if a cast resulting from that interpretation is ill-formed. If a conversion can be interpreted in more than one way as a static_cast followed by a const_cast, the conversion is ill-formed. -- Seungbeom Kim [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: nabulke on 25 Feb 2010 19:50 On 26 Feb., 09:57, Brendan <catph...(a)catphive.net> wrote: > What's the precise difference between C style casts, and static_cast. > I've always been told that static_cast and const_cast casts are > better, but I'd like to know exactly in what circumstances they differ > so I can make that judgement myself. [excess quoting deleted -mod] Please check this: http://stackoverflow.com/questions/28002/regular-cast-vs-static-cast-vs-dynamic-cast http://stackoverflow.com/questions/1609163/what-is-the-difference-between-static-cast-and-c-style-casting http://stackoverflow.com/questions/32168/c-cast-syntax-styles Hope this helps -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Francis Glassborow on 26 Feb 2010 05:30 Seungbeom Kim wrote: > Brendan wrote: >> O wise and powerful clcm, >> >> What's the precise difference between C style casts, and static_cast. >> I've always been told that static_cast and const_cast casts are >> better, but I'd like to know exactly in what circumstances they differ >> so I can make that judgement myself. >> >> Giving me a reference to something in the C++ standard is fine... > > ISO/IEC 14882:2003, 5.4/5: > > The conversions performed by > � a const_cast (5.2.11), > � a static_cast (5.2.9), > � a static_cast followed by a const_cast, > � a reinterpret_cast (5.2.10), or > � a reinterpret_cast followed by a const_cast, > can be performed using the cast notation of explicit type conversion. > [...] If a conversion can be interpreted in more than one of the ways > listed above, the interpretation that appears first in the list is used, > even if a cast resulting from that interpretation is ill-formed. > If a conversion can be interpreted in more than one way as a static_cast > followed by a const_cast, the conversion is ill-formed. > -- > Seungbeom Kim And a major difference is that you cannot remove a const (or volatile) qualification by using a static_cast. This gives added protection and allows us to write const-correct code which the compiler can check for us. Another subtle difference is when casting pointers. A static-cast can modify the pointer in ways that a C-style cast will not. This can be significant when dealing with multiple inheritance. -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Seungbeom Kim on 26 Feb 2010 05:31
Seungbeom Kim wrote: > Brendan wrote: >> O wise and powerful clcm, >> >> What's the precise difference between C style casts, and static_cast. >> I've always been told that static_cast and const_cast casts are >> better, but I'd like to know exactly in what circumstances they differ >> so I can make that judgement myself. >> >> Giving me a reference to something in the C++ standard is fine... > > ISO/IEC 14882:2003, 5.4/5: > > The conversions performed by > � a const_cast (5.2.11), > � a static_cast (5.2.9), > � a static_cast followed by a const_cast, > � a reinterpret_cast (5.2.10), or > � a reinterpret_cast followed by a const_cast, > can be performed using the cast notation of explicit type conversion. > [...] If a conversion can be interpreted in more than one of the ways > listed above, the interpretation that appears first in the list is used, > even if a cast resulting from that interpretation is ill-formed. > If a conversion can be interpreted in more than one way as a static_cast > followed by a const_cast, the conversion is ill-formed. I forgot to add this, which may be relevant: 5.4/7: In addition to those conversions, the following static_cast and reinterpret_cast operations (optionally followed by a const_cast operation) may be performed using the cast notation of explicit type conversion, even if the base class type is not accessible: � a pointer to an object of derived class type or an lvalue of derived class type may be explicitly converted to a pointer or reference to an unambiguous base class type, respectively; � a pointer to member of derived class type may be explicitly converted to a pointer to member of an unambiguous non-virtual base class type; � a pointer to an object of non-virtual base class type, an lvalue of non-virtual base class type, or a pointer to member of non-virtual base class type may be explicitly converted to a pointer, a reference, or a pointer to member of a derived class type, respectively. This states that the C-style cast can do something that C++-style casts cannot do. -- Seungbeom Kim [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] |