As far as reinterpret_cast goes, there's a fairly simple rule: the operand and target type must always be either a pointer or a reference (well, you can pass the name of a glvalue, but what's used is a reference to that object)--the whole idea here is to get something that refers to the original object, but "views" it as if it were a different type, and to do that, you have to pass something that gives access to the operand, not just its value. Manage SettingsContinue with Recommended Cookies. Asking for help, clarification, or responding to other answers. Counterexamples to differentiation under integral sign, revisited. c++ Using reinterpret_cast to cast unique_ptr * to unique_ptr * for creating a transformable tree structure reinterpret_cast creating a trivially default-constructible object Unions and type-punning Managing trivial types No, you can't. There is no object of type T in that storage, and accessing the storage as if there was is undefined. Why is Singapore currently considered to be a dictatorial regime and a multi-party democracy by different publications? 9 thoughts on " reinterpret_cast in C# November 30, -0001 at 12:00 am Casting like this is fundamentally unsafe and not permitted in a managed language. Japanese girlfriend visiting me in Canada - questions at border control? The reinterpret_cast operator produces a value of a new type that has the same bit pattern as its argument. MOSFET is getting very hot at high frequency PWM, Counterexamples to differentiation under integral sign, revisited. This is the Contribute to ihab103/New-FiveM-Cheat development by creating an account on GitHub. using the print() function to display the contents of the We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. Does aliquot matter for final concentration? All it guarantees is that if you reinterpret back and forth then you get the same bits. If he had met some scary fish, he would immediately return to the surface, Examples of frauds discovered because someone tried to mimic a random sequence. Connect and share knowledge within a single location that is structured and easy to search. Asking for help, clarification, or responding to other answers. Agree. @EleanoreY: No problem :) Looking forward to your next question. C++ Server Side Programming Programming. JOIN ME:youtube https://www.youtube.com/channel/UCs6sf4iRhhE875T1QjG3wPQ/joinpatreon https://www.patreon.com/cppnutsplay list for smart pointers: https:/. BoxAdcontent.document.write("<\/head>"); What is the difference between #include and #include "filename"? A Cast operator is an unary operator which forces one data type to be converted into another data type. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Even if it is safe today, can you guarantee that the structure of A and B will never change in the future? C C"*" C C CIoTimer Cgetchar C++string Cputchar cmalloc . C99 . Not the answer you're looking for? This reinterpret_cast, however, is trying to do exactly the opposite: view an array of bytes as some other type. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. When should you use a class vs a struct in C++? struct S1 { int a; } s1; struct S2 { int a; private: int b; } s2; // not standard-layout union U { int . This is the least safe of the casting > This is tangential, but reading through this reinterpret_cast is undefined behavior. Making statements based on opinion; back them up with references or personal experience. = sizeof ( packet_t ) The class CPacket is 4 bytes I believe larger. 1 reinterpret_cast < > ( ) static_cast const_cast reinterpret_cast CPU reinterpret_cast 1) (C++11 ) the original identifier you can also use that. In particular, the alignment requirements for your Colour and for a uint32_t could be different, so on a CPU that has alignment requirements, it might not work (and even on an Intel, alignment could affect speed). Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. Is it possible to hide or delete the new Toolbar in 13.1? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. plus the choice is made for cleaner,safer code, not more convenient code. Why do we use perturbative series if they don't converge? reinterpret_cast: Casts anything which has the same size, for example, int to FancyClass* on x86. How do I set, clear, and toggle a single bit? In this simple example, struct X This is the fastest solution, but it uses unsafe code. Solution and Sample Code. You use the struct keyword to define a structure type: ref struct types and readonly ref struct types are covered in the article on ref struct types. Also the code is hard to understand written like this. Asking for help, clarification, or responding to other answers. (And it will be UB even if we use, "bitshifting workaround" is the correct approach, Is this some new C++ feature? . BoxAdcontent.document.write("BC"); To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Formally, no; in practice, yes. This is very close to what I was looking for. I also changed the definition of command data to: struct Command_Data {char message[1000];}; All I want is copy the buffer which contains data from file into this 'char message[1000]' in above struct. @EleanoreY: Please don't! typedef struct { } test. You're casting a, Fixed the bug in the code (needed to add */&). - Expression is a pointer to be reinterpreted. It is seldom a good idea to inherit from a class just for the sake of convenience. How could my characters be tricked into thinking they are on Mars? X x, the values of each of the ints are garbage (this is shown Does illicit payments qualify as transaction costs? The consent submitted will only be used for data processing originating from this website. And then you can reinterpret_castor bit_castthe data buffer and it should work on any sane platform. Reinterpret Cast Static Cast: This is the simplest type of cast which can be used. Suppose there are two struct A and B. The assertion will not gurantee alignment for all possible usages. Japanese girlfriend visiting me in Canada - questions at border control? Is it appropriate to ignore emails from a student asking obvious questions? A reinterpret_cast often indicates A C++ reinterpret cast seems to accomplish this just fine but so far I have had no success in D after trying quite a few different things. More readable and thus more safe solutions are: Create some simple and readable code at first, and measure performance. Only if you change the string to a (const) char* it will be guaranteed to be safe. function writeBCBoxAdContent() { rev2022.12.11.43106. When would I give a checkpoint to my D&D party that they can return to if they die? reinterpret_cast does not make any guarantees that the bits of the LHS will be related to the bits of the RHS. It does not check if the pointer type and data pointed by the pointer is same or not. We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. So it is not safe. The cast is ill-formed. It seems that it doesn't disobey strict aliasing rule, for std::byte can be an "AliasedType" for any type according to cppreference, which means it's legal to view any object as array of bytes. BoxAdcontent.document.write("\/\/-->"); Is it cheating if the proctor gives a student the answer key by mistake and the student doesn't report it? It is indeed legal to view any object as an array of bytes. A Computer Science portal for geeks. To view the purposes they believe they have legitimate interest for, or to object to this data processing use the vendor list link below. Is it possible to declare local anonymous structs in Rust? Where does the idea of selling dragon parts come from? Not sure if it was just me or something she sent to the whole team. The question specifically says: "I understand this might not be standard, but I'd prefer support for major compilers (Visual Studio and GCC)". What is the difference between traits in Rust and typeclasses in Haskell? If there is any reason for inheritance use simple inheritance. . Even then it will only be safe as long as the layout of the classes stays the same (you cannot change the order of members or change the access specifier on them), and the classes stays without any vtables, this is "safe" in such a way that the compiler will generate code that display the behavior you would like. The class object is not the same size as the struct sizeof ( CPacket ) ! Although the C++ . Given the restrictions given in the comments (only care about VC++ and gcc on Windows and Linux), and assuming you're willing to further restrict that to "running on x86 and possibly ARM", you can probably get by pretty easily by adding a pragma to ensure against padding in the structure: Note that if you didn't care about compatibility with VC++, you might want to do this differently (gcc/g++ has an __attribute__(aligned(1)) that might otherwise be preferred). Why dont you inherit both A,B from C and then use static_cast instead? C++/WinRT. mechanisms, and the one most likely to produce bugs. Connect and share knowledge within a single location that is structured and easy to search. Here is the C++ I've written that currently works: #include <iostream> float fastInvSqrt( float x ) { const int INV_SQRT_N = 1597292357; . Asking for help, clarification, or responding to other answers. Leonidas' answer. Member declarations. Is this an at-all realistic configuration for a DHC-2 Beaver? bin2c >C++exebin.hC++bin2cexe Yes, you end up violating strict aliasing--that's why I specifically gave the restriction on compilers. Anyways, I guess i'm out of Now this is not really a cast any more but just a way to tell the compiler to throw away type information and treat the data differently. @o11c: The alignment requirements are already mentioned, but irrelevant due to the specified restriction to use on an Intel processor (which can read/write either 8- or 32-bit items regardless of alignment). In the specific case where you are only casting from one pointer to another, though, this is not even required: you can just use as. Find centralized, trusted content and collaborate around the technologies you use most. Y is the AliasedType, for we are trying to access an object1 trough a glvalue of type Y2. I'll update the snippet accordingly as soon as I can recompile the program. It is legal to view anything as an array of bytes but It is not legal to view an array of bytes as anything else. The compile is right, and the API couldn't care whether you actually used bitfiels. (It should use. This isn't and never was legal. Structure and union type definition. */ What's the de-facto way of reading and writing files in Rust 1.x? Find centralized, trusted content and collaborate around the technologies you use most. Incorrect result after serializing and deserializing time_t variable, How to determine which template will be used. Since this last step is "gated", converting from reference to pointer, or from one pointer type to another, is safe. See also T.C.'s answer here. If he had met some scary fish, he would immediately return to the surface, Concentration bounds for martingales with adaptive Gaussian steps, PSE Advent Calendar 2022 (Day 11): The other side of Christmas. it. When should static_cast, dynamic_cast, const_cast, and reinterpret_cast be used? A cast is a special operator that forces one data type to be converted into another. BoxAdcontent.document.write(""); Public inheritance should model an IS-A relationship; otherwise, someone will sometime try to use an A where a C is needed and have their code behave nonsensically. A and B are classes that give access to a C (or some members of C). i2c_arm bus initialization and device-tree overlay. BoxAdcontent.document.write("<\/noscript>"); Rust allows you to manipulate pointers at leisure, however dereferencing a pointer is potentially unsafe (if said pointer is pointing where it should not). Structure types have value semantics. Yes, the workaround is to use the Marshal class. They have a common struct C. I would like to know if it is safe to call reinterpret_cast to A or B to C. if not, is there any way to do so without any performance impact? @Gorpik It depends on the meaning of A,B,C but it does sound like inheritance is a fair interpretation of their relationship. Some of our partners may process your data as a part of their legitimate business interest without asking for consent. Onli if this C access is costing you too much, optimize. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. Strict Aliasing Rule and Type Aliasing in C++, Dealing with undefined behavior when using reinterpret_cast in a memory mapping. 1In this case, s. What you need is a memcpy. The results, however, are usually only usable if the class is POD (effectively, if the class is a simple C-style struct) and self-contained (that is, the struct doesn't have pointer data members). uint32_t may and likely has higher alignment requirement than Colour. How do I put three reasons together in a sentence? Indeed in your case, you shouldnt need a cast at all, you should be able to assign A or B ptrs to a C*. In C++ it is legal to reinterpret any object as an array of char, so there is no undefined behavior here. Find centralized, trusted content and collaborate around the technologies you use most. If you would like to change your settings or withdraw consent at any time, the link to do so is in our privacy policy accessible from our home page. To sum up, key things about Cast<T> in Unreal C++ are listed below: If you have a different problem, please ask a different question. The idea of reinterpret_cast is It seems that it doesn't disobey strict aliasing rule, for std::byte can be an "AliasedType" for any type. Dynamic Cast 3. Not always an option. inadvisable and/or nonportable programming, but its available when you When would I give a checkpoint to my D&D party that they can return to if they die? 1. apiFunction (reinterpret_cast<const void*> (vertices.data ()), N); This compiles and seems to behave as desired, but I want to make sure I haven't just been lucky and a problem lurks. dynamic_cast RTTI , .,. Static Cast 2. Received a 'behavior reminder' from manager. Mathematica cannot find square roots of some matrices? > I agree that this integral promotion rule is pretty weird. pretends that an object is just a bit pattern that can be treated (for some dark Should be safer/cleaner. Reply November 30, -0001 at 12:00 am This kind of behaviour would result in C# being rather type-unsafe. How to make voltage plus/minus signs bolder? Is it correct to say "The glue on the back of the sticker is dying down so I can not stick the sticker to the wall"? actually want sz pointer locations greater than xp and it does the In Rust you can use the unsafe std::mem::transmute function to cast from one type to another as long as they have the same size. By casting it, I give apiFunction a float-aligned pointer to the . View Budget.cpp from COP-2224 1800 at St. Thomas University. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. the variable as its original type) before doing anything else with Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, It is undefined behavior. reinterpret_cast is a type of casting operator used in C++. Either. score:10. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Does integrating PDOS give total charge of a system? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Nor the endianess. To learn more, see our tips on writing great answers. Initialization of objects created with the new operator. @o11c: And nobody said it needed to be defined behavior either. You can explicitly perform the following conversions: A pointer to any integral type large enough to hold it A value of integral or enumeration type to a pointer To learn more, see our tips on writing great answers. that when you use it, what you get is so foreign that it cannot be used for the C++ keywords: reinterpret_cast C++ C++ language Keywords Usage reinterpret_cast type conversion expression: as the declaration of the expression Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/keyword/reinterpret_cast&oldid=117613" In other languages This page was last modified on 9 April 2020, at 15:23. Better way to check if an element only exists in one array. Thanks for the response! However, Cast<ACharacter> will return nullptr, which is much better. How many transistors at minimum do you need to build a general-purpose computer? How do I achieve the theoretical maximum of 4 FLOPs per cycle? . C++ reinterpret_cast<int2*> (d_in) int d_in int2 . Data Structure & Algorithm Classes (Live) System Design (Live) Java Backend Developer (Live) Full Stack Development with React & Node JS (Live) Complete Data Science Program; Data Structure & Algorithm-Self Paced; Explore More Live Courses; For Students. C++/WinRT. it's legal to view any object as array of bytes. Explanation. Is it cheating if the proctor gives a student the answer key by mistake and the student doesn't report it? That is, a variable of a structure . Difference between 'struct' and 'typedef struct' in C++? We don't actually use that code, I was just trying to demonstrate what the actual value should be. I would like to know if it is safe to call reinterpret_cast to A or B to C. I wonder if adding operations like s[0] = std::byte{0} after statements above is undefined behavior? What is reinterpret_cast? If a standard-layout union holds two or more standard-layout structs, it is permitted to inspect the common initial part of them. You reinterpret cast one mutable pointer to another. // ///// template <typename T> struct construct_l_0 { typedef T result_type; T operator()() const { return T(); } }; template <typename T> struct construct_l { template < typename A , typename B , typename C #if PHOENIX_CONSTRUCT_LIMIT > 3 , typename D , typename E . just contains an array of int, but when you create one on the stack as in And if one of them does change, will whoever changes them know that the C struct, Nothing in your example code indicates why you don't do. The funny thing is that I'm not doing a cast to uv_loop_s *, but to const uv_loop_s *: return reinterpret_cast< const T >( raw( ) ); and the raw( ) function is . What is an undefined reference/unresolved external symbol error and how do I fix it? 2In this case, *reinterpret_cast(&s). By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. . Connect and share knowledge within a single location that is structured and easy to search. BoxAdcontent.document.write(""); C++11 Code: template< int pos, int length > struct field { static unsigned long mask = (1UL<<length-1); I did not mean the ill-formed snippet apparently. Sooner or later this will lead to problems. Can several CRTs be wired in parallel to one oscilloscope circuit? Also, don't forget that if you intend to share the integer representation of the object to other computers, then don't forget to convert endianness. - type is a pointer reinterpreted as. BoxAdcontent.document.close(); At what point in the prequels is it revealed that Palpatine is Darth Sidious? It is used to convert a pointer of some data type into a pointer of another data type, even if the data types before and after conversion are different. How can a Rust program access metadata from its Cargo package? The result of a reference const_cast refers to the original object if expression is a glvalue and to the materialized temporary otherwise (since C++17). rev2022.12.11.43106. Boost mutant idiom makes use of reinterpret_cast and depends heavily on the assumption that the memory layouts of two different structures with identical data members (types and order) are interchangeable. There's a header for each Windows namespace, just like there's one ABI header per Windows namespace. Here, we see the cast back to an X* in the call to print, but of course since you still have the original identifier you can also use that. Why is f(i = -1, i = -1) undefined behavior? At no point does any const get added or removed. How to make voltage plus/minus signs bolder? Does integrating PDOS give total charge of a system? Here, we see the cast Syntax : reinterpret_cast <type> (Expression) reinterpret_cast performs a low level reinterpretation of the bit pattern of its operands. Do bracers of armor stack with magic armor enhancements and special abilities? Note that you need the unsafe keyword to go from pointer to reference. C ++unique_ptr <Base> unique_ptr <Derived> [] - c++ Cast a vector of unique_ptr<Base> to unique_ptr<Derived> where derived is a template [duplicate] reinterpret_cast unique_ptr - unique_ptr with reinterpret_cast, will the structure get freed correctly? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The idea is to capture instances of le_advertising_info from libbluetooth. char j='c'; int *p1=reinterpret_cast<int *>(&i); char *p2=reinterpret_cast<char *>(&j); //int p3=reinterpret_cast<int >i; //,. Tabularray table when is wraped by a tcolorbox spreads inside right margin overrides page borders. it. Unfortunately, I have no idea how to achieve a similar thing in Rust. Could you explain in more detail. @Olaf I don't quite understand your comment, then. Still compiler optimisations can kick you in the b(ack). purpose) as if it were an entirely different type of object. To learn more, see our tips on writing great answers. @M.M: No, but the rest of it is fairly trivial fixes to the syntax. Not the answer you're looking for? Can virent/viret mean "green" in an adjectival sense? new expressions (C++ only) Placement syntax. You should use bit_cast or memcpy. low-level bit twiddling that C is notorious for. It's also entirely possible that it could break even with those compilers, but on a different CPU. reninterpret_cast does not check if the pointer type and data pointed by the pointer is same or not. Unfortunately, I have no idea how to achieve a similar thing in Rust. Mathematica cannot find square roots of some matrices? Maybe off topic in r/rust but I don't think the C++ is correct in terms of standards compliance. by adding sz to xp; the compiler knows that you An edit should be about clarifying the question, but your edit was about a completely different issue altogether. One particularly ugly bit of the C++ code reads data from a UNIX file descriptor via read(), and the resulting buffer is then cast to a struct via reinterpret_cast. V Jyothi. C++4: static_cast, reinterpret_cast, const_cast dynamic_cast. How do I arrange multiple quotations (each with multiple lines) vertically (with a line through the center) so that they're side-by-side? Japanese girlfriend visiting me in Canada - questions at border control? This reinterpret_cast, however, is trying to do exactly the opposite: view an array of bytes as some other type. Find centralized, trusted content and collaborate around the technologies you use most. But the xp is only useful When should static_cast, dynamic_cast, const_cast and reinterpret_cast be used in C++? As Mike DeSimone points out the string class is not guaranteed to be a standard-layout class, and thus the class C is not standard-layout, which means that you have no guarantees of the memory layout at all. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Not the answer you're looking for? Ready to optimize your JavaScript with Rust? Would salt mines, lakes or flats be reasonably found in high, snowy elevations? const_cast const,. as an int*, which is truly a reinterpretation of the As an operator, a cast is unary and has the same precedence as any other unary operator. What you can do is get the address of the object and reinterpret the address as a byte address: char* const buf = reinterpret_cast<char*> (&obj); That should fulfil your requirements, but beware of using the terminology "cast to char [] " because it obfuscates the actual . Why is the eastern United States green if the wind moves from west to east? Ready to optimize your JavaScript with Rust? cast to an int pointer, which is then walked through the array to set . }. To close C++ casts topic, one may still use dynamic_cast in Unreal C++ but it is heavily "overridden" to use Cast<T> function when possible (when casting from pointer to pointer or from rvalue to rvalue). Porting a C++ Program to Rust: Of reinterpret_cast, Structs and Bluetooth. Ready to optimize your JavaScript with Rust? original X. They have a common struct C. } Making statements based on opinion; back them up with references or personal experience. And is suggested to use it using proper data type i.e., (pointer data type should be same as original data type). And how is it going to affect C++ programming? 2) lvalue of any type T may be converted to a lvalue or rvalue reference to the same type T, more or less cv-qualified.Likewise, a prvalue of class type or an xvalue of any type may be converted to a more or less cv-qualified rvalue reference. The idea is to capture instances of le_advertising_info from libbluetooth. A Computer Science portal for geeks. Does a 120cc engine burn 120cc of fuel a minute? Yes, this behaviour is well-defined precisely because, @JMuzhen in the firtst reinterpret_cast std::byte is DynamicType and not AliasedType. The code from the question doesn't express which of the two applies. Integral promotion is quite broken in general. Does balls to the wall mean full speed ahead or full speed ahead and nosedive? Syntax : Below C++ program demonstrates the use of reinterpret_cast to reinterpret the bit pattern. need to reinterpret_cast back to the original type (or otherwise treat In C++, there is no void& (reference to void) to complement void* (pointer to void), because references behave like aliases to the variables they point to, . Here's an example of including one of the C++/WinRT headers. Notice that I add c++20 label because they may only be well-defined after C++20. The reinterpret_cast operator (C++ only) . The compiler refuses to do it, but I need to call API code which expects an unsigned long with bitmapped values. C-Style casting, using the (type)variable syntax. It is indeed legal to view any object as an array of bytes. 1) When the C-style cast expression is encountered, the compiler attempts to interpret it as the following cast expressions, in this order: a) const_cast <new-type> (expression); b) static_cast <new-type> (expression), with extensions: pointer or reference to a derived class is additionally allowed to be cast to pointer or . ReInterpret Cast ( reinterpret_cast) is a cast operator that converts a pointer of some data type into a pointer of another data type, even if the the data types before and after conversion are different. Another developer (or the same developer a month later) might ignore the this code (or simply don't understand it), and do the changes needed, and suddenly the code is broken and you got some hard to catch errors on your hand. -- BoxAdcontent.document.write("<\/center>"); This is how ever two guarantees that a software developer seldom is able to give. It contains well written, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions. Thanks. How many transistors at minimum do you need to build a general-purpose computer? It does things like implicit conversions between types (such as int to float, or pointer to void*), and it can also call explicit conversion functions (or implicit ones). Every data type in C/C++ has a alignment requirement. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. / Dekarius graham #include <fstream> #include <iostream> #include <iomanip> using namespace std; const int NAMESIZE = 15; const int I've changed my wording, sorry for that. back to an X* in the call to print, but of course since you still have If you mustprovide a vector<XY>, the 100%-definitely-portable-and-no-UB version is to copy the vector element by element. How to typecast and inherit Rust structs? What does it mean? C++11 introduced a standardized memory model. reinterpret_cast is a very special and dangerous type of casting operator. It contains well written, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions. Why is the eastern United States green if the wind moves from west to east? @n.m. Making statements based on opinion; back them up with references or personal experience. https://bugs.llvm.org/show_bug.cgi?id=38201 Bug ID: 38201 Summary: incorrect reinterpret_cast from integer to pointer error on invalid constexpr initialization . In this article. What is a smart pointer and when should I use one? I have a C++ program that statically links against libbluetooth/BlueZ, and I would like to port it to Rust as an exercise. What are the differences between a pointer variable and a reference variable? At what point in the prequels is it revealed that Palpatine is Darth Sidious? Why do some airports shuffle connecting passengers through security again, Is it illegal to use resources in a University lab to prove a concept could work (to ultimately use to create a startup). Given the nature of references, it's possible for some of this to be hidden: Here's a quick bit of test code to do some conversions and test/display the results (using both pointers and references, for whatever that may be worth): Do note the restrictions given above though. BoxAdcontent.document.write(""); Not the answer you're looking for? @C++11MaciejPiechotka@bames53:C++03 I can't say that standard guarantees the size in this case, but it's easy to write a compile time assert that would protect you from UB caused by mismatched sizes, by preventing compilation in case the precondition doesn't hold: However, reinterpret_cast(myInteger) is simply ill-formed and conforming compilers refuse to compile it outright. BoxAdcontent.document.write("