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diff --git a/docs/C++CASTING b/docs/C++CASTING deleted file mode 100644 index e1beb8f06..000000000 --- a/docs/C++CASTING +++ /dev/null @@ -1,111 +0,0 @@ -C++-style Casting -================= - -In C, you can cast in one of two ways: - -(type)var -type(var) - -The problem with C-style casting is that it allows a programmer to get away -with too much, and is also not designed to handle C++ classes. - -C++ has 4 types of casting in addition to allowing C-style casting. They are: - -static_cast -const_cast -dynamic_cast -reinterpret_cast - -The syntax is usually *_cast<type>(var). - -static_cast ------------ - -From my experience, this cast is closest to C-style casting for non-pointer -types as well as between some (but not all) pointer types. This type of cast, -like C-style casting, is performed at compile-time. static_cast can also do -a downcast of a derived class to a base class, but only if the base class is -not a virtual base class. Sometimes the result of this cast can become -undefined. static_cast is a bit more strict that C-style casting, though. It -disallows certain class conversions that would've been allowed with a C-style -cast. static_cast also doesn't allow you to cast to an incomplete type. In -these cases, I would try either dynamic_cast or reinterpret_cast. - -const_cast ----------- - -This cast is mainly to add or remove const-ness or volatile-ness from a -variable. This is safer than using a C-style cast to change the const-ness -of a variable. In most cases if you try to use one of the other casts and it -complains about const-ness, you will want to either use this cast instead or -wrap the other cast around this cast. An example: - -const int *a; -static_cast<void *>(a); <-- This will fail. - -To remedy the above, you would might try this: - -const int *a; -const_cast<void *>(a); <-- But this will still fail. - -The real solution is this: - -const int *a; -static_cast<void *>(const_cast<int *>(a)); - -It is not recommended to use const_cast on the this variable within a member -function of a class that is declared const. Instead you should use the mutable -keyword on the variable in the class's definition. - -dynamic_cast ------------- - -This cast can only be used on pointers or references to classes. It can cast a -derived class to a base class, a derived class to another derived class -(provided that both are children of the same base class), or a base class to a -derived class. You can also use this to cast a class to void *. This cast is -done at run-time as opposed to the other casts, and relies on C++'s RTTI to be -enabled. It is meant to be used on polymorphic classes, so use static_cast on -non-polymorphic classes. - -derived-to-base conversions are actually done statically, so you use either -dynamic_cast or static_cast on them, regardless of if the classes are -polymorphic or not. - -derived-to-derived or base-to-derived conversions, however, rely on run-time -type information, and this cast is used on those classes that are polymorphic. -This is safer than C-style casting in that an invalid pointer conversion will -return a NULL pointer, and an invalid reference conversion will throw a -Bad_cast exception. - -Note that in Anope we prefer if Anope::debug_cast is used. -This uses dynamic_cast (and checks for a NULL pointer return) on debug builds -and static_cast on release builds, to speed up the program because of dynamic_cast's -reliance on RTTI. - -reinterpret_cast ----------------- - -This cast I would use only as a last resort if static_cast isn't allowed on a -conversion. It allows for conversions between two unrelated types, such as -going from char * to int *. It can also be used to convert a pointer to an -integral type and vica versa. The sites I've read mention how the result is -non-portable, which I assume means the resulting object code is non-portable, -so since the code is compiled on many systems anyways, I don't see this as -being a huge issue. It is recommended to only use this if necessary, though. - -Links -===== - -The following links are web sites I've used to get this information, and might -describe some of the above a bit better than I have. :P - -http://www.acm.org/crossroads/xrds3-1/ovp3-1.html -http://www.cplusplus.com/doc/tutorial/typecasting.html -http://www.codeguru.com/forum/showthread.php?t=312456 -http://www.cs.umd.edu/class/sum2003/cmsc311/Notes/BitOp/cast.html -http://msdn.microsoft.com/en-us/library/5f6c9f8h(VS.80).aspx -http://en.wikibooks.org/wiki/C%2B%2B_Programming/Type_Casting -http://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=134 - --- CyberBotX, Nov 23, 2008 |