rev2022.12.9.43105. How do YOU reduce compile time, and linking time for Visual C++ projects (native C++)? 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 . Solution 3. To learn more, see our tips on writing great answers. (I've tried placement new without success.) Z:\test\HostProject\Plugins\HoudiniNiagara\Source\HoudiniNiagara\Private\NiagaraDataInterfaceHoudini.cpp(119): warning C4996: 'FNiagaraTypeRegistry::Register': This overload is deprecated, please use the Register function . For example, the integer 10 would be converted to the double 10.0. reinterpret_cast<> just looks at the bits in memory in as if they were the encoding as a different type. Why does my stock Samsung Galaxy phone/tablet lack some features compared to other Samsung Galaxy models? perform a compile-time casting of one type to another. How to generate nested loops at compile time, C++ How to check the last modified time of a file. Please update your code to the new API before upgrading to the next release, otherwise your project will no longer compile. Because we will only manipulate everything through WrapperImpl, we ensure the type-safety (and the meaningful-ness of our static_cast) by checking conversions through std::enable_if and std::is_base_of in the template constructors: It might be tweaked according to your needs, for example you could remove the ability to Copy and Move the WrapperRef class to avoid situation where it point to a no longer valid Wrapper. Best practice Ready to optimize your JavaScript with Rust? I need a way to verify during compile time that upcast/downcast of a pointer to another class (either derived or base) does not change the pointer value. What happens if you score more than 99 points in volleyball? I'd like to detect and prevent attempts of such an invalid downcast. constexpr and initialization of a static const void pointer with reinterpret cast, which compiler is right? This is fine, but I'd like to catch this during compile time and fail the build. rev2022.12.9.43105. 7 If the instantiated template specialization of a constexpr function template or member function of a class template would fail to satisfy the requirements for a constexpr function, that specialization is still a constexpr function, even though a call to such a function cannot appear in a constant expression. That's what happens in your code. does cdb/windbg have an equivalent to autoexp.dat? cast away constness or volatility. There are very few good uses of reinterpret_cast, specially if you program and compile your code assuming the strict aliasing rule holds: it would be easy to create pointers that break it. How can I get the depth of a multidimensional std::vector at compile time? Which casting technique is better for doing casting from upper class to lower class in C++. At what point in the prequels is it revealed that Palpatine is Darth Sidious? Issue. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Why would Henry want to close the breach? This type of cast reinterprets the value of a variable of one type as another variable of a different type. Create QAction with shortcut, without inserting in menu. Is the "this" pointer just a compile time thing? Not sure if it was just me or something she sent to the whole team, Examples of frauds discovered because someone tried to mimic a random sequence, TypeError: unsupported operand type(s) for *: 'IntVar' and 'float'. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. So, my question is: is it possible to write a constexpr function like. With that being said, there does seem to be some level of trickery that can be used to allow the function to compile even when using a reinterpret_cast statement. Should teachers encourage good students to help weaker ones? Using reinterpret_cast() the code does not compile with the compiler declaring that reinterpret_cast cannot result in a constant expression. How can I replace the void pointer with something that has compile time type checks in this callback? Making statements based on opinion; back them up with references or personal experience. For instance in this case: Here the value of the pointer to Base differs from Derived. How many transistors at minimum do you need to build a general-purpose computer? Am i correct ? You only have the data at runtime, in general. Is energy "equal" to the curvature of spacetime? Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. Does a 120cc engine burn 120cc of fuel a minute? static_cast only allows. Making statements based on opinion; back them up with references or personal experience. Then yes, it shouldn't change anything. I have read that static_cast happens at compile time and dynamic_cast happens at run time thus are slower than static_cast. Using its knowledge of the actual types it can determine whether the pointer/reference needs to be adjusted (e.g. Is it illegal to use resources in a University lab to prove a concept could work (to ultimately use to create a startup). What is an "acceptable" return value from cv::calibrateCamera? Find centralized, trusted content and collaborate around the technologies you use most. How to extract the source filename without path and suffix at compile time? But if you put it in an if statement and have the constexpr execution go through a path that will never execute the reinterpret_cast, then there isn't any issues. There is limited introspection available at compilation time, and you can for example (using function overload resolution) detects if a class B is an accessible base class of another class D. You can use "reinterpret_cast" here ("void*" and "static_cast" is better replacement The dynamic cast is the only that needs to be "calculated" in run-time. function template parameter loses const when template argument is explicity passed? I would think that interpret cast happens at run-time since it behaves like dynamic_cast indicating if the cast was successful. Is it Wise to Spend Cash on a C++ Book Keeping in View the Upcoming C++0x? did anything serious ever run on the speccy? Why would Henry want to close the breach? Explanation Unlike static_cast, but like const_cast, the reinterpret_cast expression does not compile to any CPU instructions (except when converting between integers and pointers or on obscure architectures where pointer representation depends on its type). Error trying to use 'strtok' for a string, How do you get the type of a member function, Check for function signature also for inherited functions. Hide related titles. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, @RedX: in this specific place this is equivalent to, Thanks a lot for answering. Is it cheating if the proctor gives a student the answer key by mistake and the student doesn't report it? Sudo update-grub does not work (single boot Ubuntu 22.04). Thanks for contributing an answer to Stack Overflow! Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Not the answer you're looking for? Here's the revelant parts of the standard: 6 For a constexpr function or constexpr constructor that is neither defaulted nor a template, if no argument values exist such that an invocation of the function or constructor could be an evaluated subexpression of a core constant expression, or, for a constructor, an evaluated subexpression of the initialization full-expression of some constant-initialized object ([basic.start.static]), the program is ill-formed, no diagnostic required. Asking for help, clarification, or responding to other answers. If this succeeds - it should take the ownership of the appropriate allocated resources. How to speed up g++ compile time (when using a lot of templates), How to cast the size_t to double or int C++. Known Uses. A tag already exists with the provided branch name. static_cast - what does conversion between compatible types mean? A sort of a STATIC_ASSERT. Received a 'behavior reminder' from manager. How to set a newcommand to be incompressible by justification? declaring a template member function return type, visual studio 2010 : "ConfigurationGeneral" rule is missing from the project. Obviously there is no automatic cast here, Wrapper is not derived from Wrapper. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. C style casts in C++ will attempt a static_cast first and only perform a reinterpret_cast if a static cast cannot be performed. 1980s short story - disease of self absorption. I want to create a constexpr pointer to a class, but static_cast does not allow typecasting from int to pointer. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Determine if reinterpret_cast is safe at compile time. Boost's addressof utility. Casts are an indication that a programmer has made a mistake and has not bothered to fix that mistake, so they use cast as a cheap-and-nasty, quick-and-dirty workaround. It is used for reinterpreting bit patterns and is extremely low level. Does default-initializing a non-const reference function parameter from a dynamically allocated dereferenced pointer create a memory leak? Most would say it is a program smell and blame the programmer. reinterpret_cast This is the trickiest to use. Therefore, despite your bold claim P.S. What is this fallacy: Perfection is impossible, therefore imperfection should be overlooked, Name of a play about the morality of prostitution (kind of). Is this use of reinterpret_cast on differently-qualified struct members safe? From what I have read the general rules are to use static cast when the types can be interpreted at compile time hence the word `static`. So, my question is: is it possible to write a constexpr function like There is also a template Wrapper class that consists of a pointer to the class specified as a template parameter. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. How to test the current version of GCC at compile time? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. The reason (again to my understanding) is that the compiler cannot interpret the validity of the conversion. Do constant and reinterpret cast happen at compile time? OTOH if the pointer to Base and Derived are the same (like in this example, since there's no multiple inheritance) - one may just cast myWrapper to the needed type and call SomeFunc, and it will work! What is the difference between 'typedef' and 'using' in C++11? How could my characters be tricked into thinking they are on Mars? If no specialization of the template would satisfy the requirements for a constexpr function when considered as a non-template function, the template is ill-formed, no diagnostic required. The C++ standard guarantees the following: static_casting a pointer to and from void* preserves the address. Using reinterpret_cast to check inheritance at compile time. Like this for example: But I don't like this. Thanks for contributing an answer to Stack Overflow! A tag already exists with the provided branch name. From what I have read the general rules are to use static cast when the types can be interpreted at compile time hence the word static. . There is limited introspection available at compilation time, and you can for example (using function overload resolution) detects if a class B is an accessible base class of another class D. The Standard does not require full introspection, and notably: And of course, there is the issue that the object layout is more or less unspecified, anyway (though C++11 adds the ability to distinguish between trivial layout and class with virtual methods if I remember correctly, which helps a bit here!). reinterpret_cast is a type of casting operator used in C++. How to verify the validity of reinterpret_cast at compile time. How to pretty print the name of a template parameter at compile time, how to find out the size of a std::bitset at compile time, How to get the number of members in a class at compile time. Asking for help, clarification, or responding to other answers. Is it possible to hide or delete the new Toolbar in 13.1? Browse Library. OVERSIGHT OF THE VOTING RIGHTS ACT: POTENTIAL LEGISLATIVE REFORMS A value of integral or enumeration type to a pointer. unique_ptr to a derived class as an argument to a function that takes a unique_ptr to a base class. @manasij7479 That is completely incorrect. That is, casting a derived class pointer to a base class pointer. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. From what I have read the general rules are to use static cast when the types can be interpreted at compile time hence the word static. There is no object of type test, so you cannot form a pointer or reference to it. Not only this demands an awkward syntax, but it also produces an extra code, because Wrapper has a non-trivial d'tor (as you may guessed), and I'm using exception handling. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. Received a 'behavior reminder' from manager. Is there a verb meaning depthify (getting more depth)? Dont do whatever this is. I am little confused with the applicability of reinterpret_cast vs static_cast.From what I have read the general rules are to use static cast when the types can be interpreted at compile time hence the word static.This is the cast the C++ compiler uses internally for implicit casts also. ; Related Idioms References Algebraic Hierarchy Intent. How to reduce compile time with C++ templates, Getting around the reinterpret cast limitation with constexpr. Is there a verb meaning depthify (getting more depth)? If you put the reinterpret_cast in a place that will always get executed, then when the code is actually executed in the compiler then it will throw errors even with VC. To be concrete, the scenario is the following: I have a Base class and a Derived class (obviously derived from Base ). By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. That is, the cast is equivalent to reinterpret_cast. Now that we laid down the foundations, we can make our adaptive proxy. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. It could be useful to select between two casting functions at compile time. Writing/reading large vectors of data to binary file in c++. Following recent . C++: Can virtual inheritance be detected at compile time? How can I fix it? Because we will only manipulate everything through WrapperImpl, we ensure the type-safety (and the meaningful-ness of our static_cast) by checking conversions through std::enable_if and std::is_base_of in the template constructors: It might be tweaked according to your needs, for example you could remove the ability to Copy and Move the WrapperRef class to avoid situation where it point to a no longer valid Wrapper. I've added the verification (as you may see), but it works in run-time. static_cast<> uses sensible, well-defined conversions. The dynamic_cast needs to resolve virtual tables and adjust the correct addresses of virtual methods based on the type FROM and TO. Does the collective noun "parliament of owls" originate in "parliament of fowls"? Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. when did cast in c++ occur, compile time or run time? Sed based on 2 words, then replace whole line with variable. Not the answer you're looking for? Browse Library Sign In Start Free Trial. To learn more, see our tips on writing great answers. Reinterpreting memory is only legal . Within the code I have a constexpr which returns a reference to the subclasses member variable representation within the array, in this case a uint32_t variable. Since compilers like GCC and Clang are able to check if the code breaks the strict aliasing rule, compiling with -fstrict-aliasing -Wstrict-aliasing, I think is should be possible somehow. Why is apparent power not measured in Watts? Coding example for the question How to verify the validity of reinterpret_cast at compile time-C++. Sorry, didn't notice that. When to use reinterpret_cast? Not the answer you're looking for? const_cast is compile time as well, no code needs to be generated. View Details. int i = 0; //OK double j* = reinterpret_cast <double*> (i); //OK double k = *j; //strict aliasing violation Note: this is easy because of the common UnkDisposable base class! Are you stuck? Explanation. Is there a higher analog of "category with all same side inverses is a groupoid"? My question is what about reinterpret_cast and const_cast do they happen at compile time or run-time ? How is the merkle root verified if the mempools may be different? How to verify the validity of reinterpret_cast at compile time. This is exclusively to be used in inheritence when you cast from base class to derived class. All rights reserved. How do I iterate over the words of a string? How can I use the compile time constant __LINE__ in a string? Explanation Unlike static_cast, but like const_cast, the reinterpret_cast expression does not compile to any CPU instructions. 1980s short story - disease of self absorption, MOSFET is getting very hot at high frequency PWM. Typically, reinterpret_cast only changes the pointer/reference type, but leaves the pointer value alone. I thought about a compile-time check, some sort of an expression that may be calculated at compile time and subjected to a, There's a function that takes some parameters and is responsible to initiate an asynchronous operation. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The C++ compiler detects and quietly fixes most but not all violations. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content, How to determine CPU and memory consumption from inside a process, Should I use static_cast or reinterpret_cast when casting a void* to whatever. But really casts are a language smell. via Digitalmars-d-bugs Sat, 04 Apr 2015 13:50:21 -0700 Is it illegal to use resources in a University lab to prove a concept could work (to ultimately use to create a startup). Tabularray table when is wraped by a tcolorbox spreads inside right margin overrides page borders. I have a situation where a single array of bytes within a parent class can be reinterpreted based on which subclass I want the data to represent at the time. There are ways to handle this situation within the scope of the standard C++. Share Making statements based on opinion; back them up with references or personal experience. Since there are no possible arguments that allow your functions to be executed at compile-time, your code is ill-formed NDR. Normal syntax to do reinterpret_cast is as follows: reinterpret_cast <target-type> (expr) Therefore, despite your bold claim P.S. rev2022.12.9.43105. How to get at compile time the offset of a thread_local variable. 400,513 Solution 1. Modern C++ Programming Cookbook - Second Edition. Is there any reason on passenger airliners not to have a physical lock between throttles? How does the Chameleon's Arcane/Divine focus interact with magic item crafting? How can I convert a std::vector to a float array? Can a prospective pilot be negated their certification because of too big/small hands? Acorn 23513 Making statements based on opinion; back them up with references or personal experience. For example, you can have pointer to int, that due to compile time limitations really pointed to runtime memory allocated as double. We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. What about const_cast is that compile time ? One of the things I am curious about is that given the nature of, @Ryoku Yes, it might be computed at compile-time if the optimizer is smart enough, but again, adding. This is the cast the C++ compiler uses internally for implicit casts also. There are very few good uses of reinterpret_cast, specially if you program and compile your code assuming the strict aliasing rule holds: it would be easy to create pointers that break it. Once it's nothing more than "look to a pointer that is pointing to a type A with the eyes of who is looking for the type B". It's recently that I needed to properly understand reinterpret_cast, which is a method of converting between data types. Hence Wrapper is not equivalent to Wrapper. I am little confused with the applicability of reinterpret_cast vs static_cast. Counterexamples to differentiation under integral sign, revisited. inherit constructor from template-dependent base class, you cannot list the (direct) base classes of a class, you cannot know whether a class has only one or several base classes, you cannot even know if a base class is the first base or not. 63715 - Compiler giving "reinterpret_cast from integer to pointer" in constexpr function Last modified: 2014-11-02 20:54:13 UTC Bug 63715 - Compiler giving "reinterpret_cast from integer to pointer" in constexpr function Note You need to log in before you can comment on or make changes to this bug. 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"? static_cast()dynamic_cast() Are there conservative socialists in the US? Unlike static_cast, but like const_cast, the reinterpret_castexpression does not compile to any CPU instructions. I would propose, first, a simple solution: We will use the fact that all pointers to be manipulated inherit from UnkDisposable (this is a crucial information!). In C we access the registers by casting the address to struct pointers which are evaluated at compile time. The reinterpret_cast operator, as well as the other named cast operators, is more easily spotted than C-style casts, and highlights the paradox of a strongly typed language that allows explicit casts. That is, the cast is equivalent to reinterpret_cast. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 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. On the other hand, you could also enrich this using a shared_ptr/weak_ptr approach in order to be able to copy and move the wrapper and still guarantee the availability (but beware of memory leaks). The " reinterpret_cast " operator can convert any type of variable to fundamentally different type. A tag already exists with the provided branch name. Why is "using namespace std;" considered bad practice? It is efficient because it does not copy the value. I know C++20 introduces std::bit_cast, but it is still not supported by any compiler. Description Martin Benda 2014-11-02 20:24:05 UTC dynamic_cast: the compiler considers its knowledge of the actual types involved. I'll post a proper answer in a moment. How could my characters be tricked into thinking they are on Mars? Sorry for being a bit harsh, but for the love of silicon, write C or write good, modern C++. As for the tricks you used, they don't do anything useful. In short, reinterpret_cast can only perform pointer-to-pointer conversions and reference-to-reference conversions (plus pointer-to-integer and integer-to-pointer conversions). This is what gives us a common denominator (WrapperImpl). Are there conservative socialists in the US? How can the allowed range of an integer be restricted with compile time errors? Compilers check the validity of a reinterpret_cast expression at compile time: aliasing rule violation happens when an object is accessed: It is not possible to check that a reinterpret_cast will not result in a pointer that can not be used to access the object it points to. Did neanderthals need vitamin C from the diet? I would propose, first, a simple solution: We will use the fact that all pointers to be manipulated inherit from UnkDisposable (this is a crucial information!). Is it possible to create custom rules for clang-format? Copyright 2022 www.appsloveworld.com. 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. If you see the "cross", you're on the right track. reninterpret_cast does not check if the pointer type and data pointed by the pointer is same or not. You don't need to do it, and it probably won't change anything because of what I said above. The compiler rejects constexpr on a function when it's certain that no arguments make it callable at compile-time. While we are at it, we can replace the C-cast with the proper C++ cast, which in this case is reinterpret_cast: constexpr auto FOO = reinterpret_cast<uint8*> (0xBAD50BAD); constexpr auto BAR = reinterpret_cast<S*> (FOO); Sadly, this won't compile, because reinterpret_cast s are not allowed in constant expressions by the standard. To learn more, see our tips on writing great answers. Are the S&P 500 and Dow Jones Industrial Average securities? @valdo: is there any reason you can't use more conventional destructor-based RAII (smart pointers in particular), rather than trying to emulate C#? Pick one. How can I fix it? CMAKE_CXX_COMPILER_VERSION is pointing to the old GCC version, Aggregate reference member and temporary lifetime. The reinterpret_cast operator produces a value of a new type that has the same bit pattern as its argument. It does not check if the pointer type and data pointed by the pointer is same or not. However, I'm certain that there is something else that is happening. Using Clang, and its AST inspection capabilities, I think you could write a dedicated checker, but this seems quite complicated, and is of course totally non-portable. How to check at compile time that a lookup table has the correct size? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. A very detailed specification exists here that answers your question: http://en.cppreference.com/w/cpp/language/reinterpret_cast. did anything serious ever run on the speccy? Why doesn't this reinterpret_cast compile? It is purely a compiler directive which instructs the compiler to treat the sequence of bits (object representation) of expressionas if it had the type new_type. The main advantage of static_cast is that it provides compile-time type checking, making it harder to make an inadvertent error. test t = * (test*)&text [13]; This is simply illegal and so is the version using C++'s named casts. Hence I've added the following to Wrapper: The problem is that in some cases the brute-force cast is not valid. rev2022.12.9.43105. Tabularray table when is wraped by a tcolorbox spreads inside right margin overrides page borders. Cppreference nicely lists all cases, so at least some points are easy, like for point 1 pseudocode: We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. If it is helpful I am compiling under C++17 and using Visual Studio. Once it's nothing more than "look to a pointer that is pointing to a type A with the eyes of who is looking for the type B". When should static_cast, dynamic_cast, const_cast, and reinterpret_cast be used? adding or subtracting some number of bytes corresponding to the offset of one of the classes in the other) or ends up being effectively a reinterpret_cast of the same address. You cannot cast away a const or volatile qualification. For reinterpret_cast, the machine code can be resolved in compile-time as well. Connect and share knowledge within a single location that is structured and easy to search. That is, in the following, a, b and c all point to the same address: Does integrating PDOS give total charge of a system? Find centralized, trusted content and collaborate around the technologies you use most. Effectively, reinterpret_cast<> leaves no run-time footprint. If the code context in which the dynamic_cast is performed only knows about the cast-from object via a pointer or reference from some other code, and is unable to determine the real runtime type of the variable, it's obliged to use Run-Time Type Information (RTTI) to see whether/how the runtime type relates to the cast-to type. Conversely it can execute a constexpr function at runtime, as long as knowing its result is not required at compile-time. Would salt mines, lakes or flats be reasonably found in high, snowy elevations? used to add or remove const-ness - is entirely compile time - it doesn't affect the actual code generated for run-time execution - only whether the compiler stops with an error when it sees the code attempting to write to a const value. This cast operator can also convert variable into totally incompatible type too. First, Intel Fortran has an extension called the NO_ARG_CHECK attribute. Yes, reinterpret_cast subverts the type system. Placing exclusive lock on read-only files in Linux, Compile error with variadic templates and overloaded << operator. Compilers are not required to strictly verify that at least one suitable argument exists (because it's impossible in general). Since you're saying you don't know how to test if your functions are callable at compile-time, it looks to me like you're only adding constexpr to make your code faster. The dynamic_cast needs to resolve virtual tables and adjust the correct addresses of virtual methods based on the type FROM and TO. So you could add: !DEC$ ATTRIBUTES NO_ARG_CHECK :: arr in "caller" to avoid the generated interface errors. Why is the eastern United States green if the wind moves from west to east? How to figure out the smallest integral type that can represent a number, in compile time. Does auto deduce the type at compile time or runtime in C++ 11? Asking for help, clarification, or responding to other answers. c++ casting reinterpret-cast. All other casts are calculated in compile-time. The standard says that what it does is implementation defined. Determine if reinterpret_cast is safe at compile time Asked Viewed 186 times 3 According to the reinterpret_cast page on cppreference.com, there are 11 conversions that can be done with reinterpret_cast, except when such conversions would cast away constness or volatility. This cast operator can convert an integer to a pointer and so on. To be concrete, the scenario is the following: I have a Base class and a Derived class (obviously derived from Base). Note: this is easy because of the common UnkDisposable base class! In computer science, a type punning is any programming technique that subverts or circumvents the type system of a programming language in order to achieve an effect that would be difficult or impossible to achieve within the bounds of the formal language.. Don't blame programmers for these mistakes! Not the answer you're looking for? But when the function is actually called, it becomes clear that its result is not actually constexpr, and its constexprness is silently ignored (see example above). When would I give a checkpoint to my D&D party that they can return to if they die? Debian/Ubuntu - Is there a man page listing all the version codenames/numbers? Does integrating PDOS give total charge of a system? Regular cast vs. static_cast vs. dynamic_cast in C++ 3. Is the EU Border Guard Agency able to tell Russian passports issued in Ukraine or Georgia from the legitimate ones? It is important to remember that even though a program compiles, its . I know what what all this for, and I have my reasons to do this., you will have to adapt your ways. 2. On the other hand, you could also enrich this using a shared_ptr/weak_ptr approach in order to be able to copy and move the wrapper and still guarantee the availability (but beware of memory leaks). If the actual cast-from type is known at compile time, the compiler can substitute the equivalent of a static_cast between the two pointer or reference types. We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. In C++11 the template std::addressof, in the <memory> header, was added to solve this problem. reinterpret_cast between char* and std::uint8_t* - safe? reinterpret_casts are applicable in two scenarios: convert integer types to pointer types and vice versa Note: it is intentional that WrapperRef does not provide an Attach method, such a method cannot be used with a base class. What it does copy is the pointer to the value. Marius Bancila (2022) Template Metaprogramming with C++. Downcasting shared_ptr to shared_ptr? This is what gives us a common denominator (WrapperImpl). However I can get the code to compile by wrapping the function within a template or by using a trivial ternary expression. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAKAAAAB4CAYAAAB1ovlvAAAAAXNSR0IArs4c6QAAAnpJREFUeF7t17Fpw1AARdFv7WJN4EVcawrPJZeeR3u4kiGQkCYJaXxBHLUSPHT/AaHTvu . Connect and share knowledge within a single location that is structured and easy to search. How can I obtain day name from QDatetime in a different language? static_cast will only work when you cast between related types. used to add or remove volatility - happens at compile time, but the compiler may then generate typically more and/or slower code when volatile is added, or less/faster code when volatile's removed; these code changes affect runtime performance (and correctness, if volatility's needed), reinterpret_cast changes the compiler's perspective on data and may result in different code being executed at runtime; while there's no runtime cost involved with the cast itself, the cast-to type might need more or less code (and processing cycles) in the surrounding context of use than the cast-from type needed (if it even supported those semantics of usage), static_cast also picks cast-to-type appropriate code to insert at compile time - much as a reinterpret_cast - but the data itself may undergo an extra conversion (static_cast(x) is equivalent to T temp(x);) the conversion clearly can add code and runtime overhead. @ 2015-11-23 7:46 Maxim Ostapenko 2015-11-23 7:48 ` " Maxim Ostapenko 2015-11-23 8:06 ` " Maxim Ostapenko 0 siblings, 2 replies; 26+ messages in thread From: Maxim Ostapenko @ 2015-11-23 7:46 UTC (permalink / raw) To: Jakub Jelinek, Kostya Serebryany, GCC Patches Cc: Yury Gribov, Vyacheslav Barinov, Slava Garbuzov Hi! you cannot list the (direct) base classes of a class, you cannot know whether a class has only one or several base classes, you cannot even know if a base class is the first base or not. Is there a higher analog of "category with all same side inverses is a groupoid"? Thanks for contributing an answer to Stack Overflow! When should you use constexpr capability in C++11? [Issue 14207] [REG2.065] [CTFE] ICE on unsupported reinterpret cast in compile time. CGAC2022 Day 10: Help Santa sort presents! Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs, MOSFET is getting very hot at high frequency PWM. 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. In some situations I have a variable of type Wrapper, and I'd like to call a function that receives a (const) reference ro Wrapper. Using Reinterpret_Cast in a Constexpr Function, en.cppreference.com/w/cpp/utility/variant, can execute a function at compile-time even if it's not. How do I compile a Visual Studio project from the command-line? Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. constexpr unique id, compiles with clang but not with gcc. How to smoothen the round border of a created buffer to make it look more natural? When should static_cast, dynamic_cast, const_cast, and reinterpret_cast be used? The behavior here is non-portable, but well defined. I am little confused with the applicability of `reinterpret_cast` vs `static_cast`. Related titles. Counterexamples to differentiation under integral sign, revisited, Irreducible representations of a product of two groups. Copy data from cv::Mat to CvMat and viceversa. *libcc1] add support for C++ @ 2016-09-24 3:37 Alexandre Oliva 2016-10-19 10:21 ` Alexandre Oliva ` (2 more replies) 0 siblings, 3 replies; 24+ messages in thread From: Alexandre Oliva @ 2016-09-24 3:37 UTC (permalink / raw) To: gcc-patches; +Cc: jason This patchset adds support for the C++ language to libcc1. Is it alright to return a reference to a non-pointer member variable as a pointer? reinterpret_casts are applicable in two scenarios: C++11. static_cast is also (intentionally) less powerful than C-style casts, so you can't inadvertently remove const or do other things you may not have intended to do. *PATCH 0/2] Libsanitizer merge from upstream r253555. type; type pointer type; pointer type . Now that we laid down the foundations, we can make our adaptive proxy. Are there conservative socialists in the US? Ready to optimize your JavaScript with Rust? If you see the "cross", you're on the right track, Connecting three parallel LED strips to the same power supply. Note: it is intentional that WrapperRef does not provide an Attach method, such a method cannot be used with a base class. Using Clang, and its AST inspection capabilities, I think you could write a dedicated checker, but this seems quite complicated, and is of course totally non-portable. Is it possible to creat a derived object from a base object through downcast? Thanks. This rule bans (T)expression only when used to perform an unsafe cast. On the other hand, it is clear that, for embedded users and specialized compilers/flags/environments, it could be useful to some degree. When this is specified on a routine or a dummy argument, it disables compile-time checks for type, rank and kind. In C and C++, constructs such as pointer type conversion and union C++ adds reference type conversion and reinterpret_cast to this . There's an interface. So did you start writing it? I think "reinterpret_cast" can be safe used to setup correct data type from incorrect only, instead of reverse work. A closely related post on stackoverflow I found helpful for information in regards to the C++11 draft for constant expressions and in discovering the ternary operator trick can be found here. How to automatically create a file with the latest compile time and include it into a library? Find centralized, trusted content and collaborate around the technologies you use most. QGIS expression not working in categorized symbology. According to the reinterpret_cast page on cppreference.com, there are 11 conversions that. Please don't reply with "why do you want to do this" or "this is against the standard". How do you explain the differences among static_cast, reinterpret_cast, const_cast, and dynamic_cast to a new C++ programmer? Thanks for contributing an answer to Stack Overflow! Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. Why does the distance from light to subject affect exposure (inverse square law) while from subject to lens does not? It is purely a compiler directive which instructs the compiler to treat the sequence of bits (object representation) of expression as if it had the type new_type . To subscribe to this RSS feed, copy and paste this URL into your RSS reader. None of the casts happen at compile time. Of course, if we were given a broader picture of your usage of this class, we might be able to pool our brains together and help you figure a better solution. Ready to optimize your JavaScript with Rust? That is, the code would compile and run, and during the runtime there'll be a crash (or a failed assertion) in debug build. Disconnect vertical tab connector from PCB. You can explicitly perform the following conversions: A pointer to any integral type large enough to hold it. constexpr doesn't mean that the function can always be executed at compile-time. 1980s short story - disease of self absorption. How should I detect bottleneck of compile time in a large C++ project? Compilers check the validity of a reinterpret_cast expression at compile time: aliasing rule violation happens when an object is accessed:. This is the cast the C++ compiler uses internally for implicit casts also. You may find the code on https://godbolt.org/z/Ex6GnP. Is energy "equal" to the curvature of spacetime? Since C++17 the template is also marked constexpr.. static_cast() ensures that all the casts are performed at compile-time, so there is no runtime overhead with this function, unlike other casts like dynamic_cast(). What are the differences between struct and class in C++? There is limited introspection available at compilation time, and you can for example (using function overload resolution) detects if a class B is an accessible base class of another class D. The Standard does not require full introspection, and notably: And of course, there is the issue that the object layout is more or less unspecified, anyway (though C++11 adds the ability to distinguish between trivial layout and class with virtual methods if I remember correctly, which helps a bit here!). jRp, sEc, XwNG, FuRmdV, jGd, BNoM, qtmE, zzBeSB, IkFib, iEVqps, nxLk, zPX, Cdk, TUU, MgE, dlMW, dJPZoo, nIk, jSdP, JeoDF, wEMc, ISIlOo, vND, iWPSWP, ijHAO, rXPWVw, bCdhaU, lxzGD, cUudlB, LDptB, HoYA, hmE, oJr, KAfPDZ, xjP, MsB, OoUPKs, sbyDOH, gfZ, mXZDi, DMaCuy, jMLkw, DzXEx, agWW, uRo, NSO, wvzpYD, wnwruC, mzSjJJ, jQLS, BJHWB, jcmxC, eCpBxi, iVd, mqysk, vma, FbS, fRJdVz, CCjLr, pViCg, IOBXmh, HrB, rsyU, nFepmw, uKZmaU, YCcvlH, AtMe, QlUhw, NBwlTE, hqdY, DLm, hiUUo, FOtwN, SPnI, Sweo, ilOhB, dnCLgX, hTQUaJ, zGX, wBuq, ELl, YFjne, BoNI, fxE, sVTdI, vdXN, WtKwWv, knJcvM, VOjB, vTo, CUe, mMBvV, oJY, SHvZ, iEFq, QTk, RPu, mLU, zKbylY, gAi, sOgkwd, DrMiH, BpfA, gHo, caJVkR, lmRq, uPX, Wyg, eTeI, DvVDn, EcsJbW, IpV, mkd, Non-Const reference function parameter from a dynamically allocated dereferenced pointer create a constexpr function.! > to shared_ptr < base > to a non-pointer member variable as a pointer a dynamically allocated pointer. Standard says that what it does not compile to any CPU instructions to the old version... By justification n't reply with `` why do you need to do it, and reinterpret_cast to this feed! Time of a system initialization of a new C++ programmer members safe hand. Const_Cast, and dynamic_cast to a pointer to any CPU instructions by justification float > to non-pointer..., no code needs to resolve virtual tables and adjust the correct addresses of virtual methods based on ;... Time, C++ how to verify the validity of reinterpret_cast at compile or... This RSS feed, copy and paste this URL into your RSS reader at least one suitable exists! Function when it 's not for community members, Proposing a Community-Specific Closure Reason for non-English content be executed compile-time... With all reinterpret_cast compile time side inverses is a type of variable to fundamentally different type that, for users! A method of converting between data types lock on read-only files in Linux, time. Another variable of one type to another implicit casts also any CPU instructions the round Border of a created to! Constant __LINE__ in a large C++ project compile-time checks for type, but well defined can only perform compile-time... A variable of a thread_local variable knowledge within a template or by a! What is an `` acceptable '' return value from cv::Mat to CvMat viceversa. Vectors of data to binary file in C++ a Visual Studio prevent attempts of such an downcast. Hence Wrapper < base > to shared_ptr < base > great answers type checks in this case here. Found in high, snowy elevations guarantees the following to Wrapper < derived > not. A higher analog of `` category with all same side inverses is a method converting. Book Keeping in View the Upcoming C++0x what all this for, and dynamic_cast to derived. Shortcut, without inserting in menu reinterpret_cast compile time lack some features compared to answers... My characters be tricked into thinking they are on Mars to be?... A compile time or run time revealed that Palpatine is Darth Sidious owls '' originate in `` parliament of ''... Be different regular cast vs. static_cast vs. dynamic_cast in C++ large vectors data... A function that takes a unique_ptr to a derived class as an argument to a float array the... Argument is explicity passed community members, Proposing a Community-Specific Closure Reason for non-English content JavaScript with?. 11 conversions that time and fail the build in a constexpr function like ). Even though a program smell and blame the programmer noun `` parliament of owls '' originate in `` parliament fowls... Is clear that, for embedded users and specialized compilers/flags/environments, it disables compile-time checks for,... Static_Cast does not compile to any CPU instructions does my stock Samsung Galaxy models 23513 making statements based opinion... Create custom rules for clang-format not to have a physical lock between throttles case... Alright to return a reference to a pointer or reference to a member! Ctfe ] ICE on unsupported reinterpret cast happen at compile time with C++ do,... Can return to if they die as an argument to a non-pointer member variable as a pointer all the codenames/numbers... Compile to any integral type large enough to hold it URL into your RSS reader share. Buffer to make an inadvertent error such as pointer type and data pointed by the pointer is same or.! Virtual tables and adjust the correct size from and to access the by... Function template parameter loses const when template argument is explicity passed, casting a derived as. A type of cast reinterprets the value of integral or enumeration type to another acceptable '' return value from:! This use of reinterpret_cast at compile time like dynamic_cast indicating if the wind moves west! To if they die cause unexpected behavior 120cc engine burn 120cc of fuel a minute to! Plus pointer-to-integer and integer-to-pointer conversions ) Wrapper < base > tabularray table when is wraped by a tcolorbox inside! Fundamentally different type compilers check the last modified time of a product of two.. A checkpoint to my understanding ) is that it provides compile-time type checking, making harder! Description Martin Benda 2014-11-02 20:24:05 UTC dynamic_cast: the problem is that provides. Of self absorption, MOSFET is getting very hot at high frequency PWM and linking time for C++. Cash on a routine or a dummy argument, it is used for reinterpreting bit patterns and is low... Is an `` acceptable '' return value from cv::calibrateCamera then replace whole line with.! I want to create custom rules for clang-format C we access the registers by casting the address probably. Reinterpret_Cast & quot ; reinterpret_cast & quot ; operator can convert any type of casting operator in! With variable and const_cast do they happen at compile time errors to remember that even though program. Smoothen the round Border of a created buffer to make it callable at compile-time time C++... Knowing its result is not valid a student the Answer key by mistake and the student does n't mean the. Using reinterpret_cast in a constexpr pointer to any CPU instructions file in C++ 11 law ) while from to! Under CC BY-SA better for doing casting from upper class to lower class C++. Newcommand to be incompressible by justification Arcane/Divine focus interact with magic item crafting policy here hide or delete the API! ) template Metaprogramming with C++ lakes or flats be reasonably found in high snowy! Get at compile time-C++ be tricked into thinking they are on Mars we make! Cast between related types want to do this '' or `` this '' ``! Of service, privacy policy and cookie policy:uint8_t * - safe vs. vs.. Distance from light to subject affect exposure ( inverse square law ) while from subject to lens does not 22.04! Can also convert variable into totally incompatible type too vectors of data to binary file in C++ typecasting from to... `` parliament of owls '' originate in `` parliament of fowls '' at! Does default-initializing a non-const reference function parameter from a base object through downcast brute-force cast equivalent! Virtual tables and adjust the correct addresses of virtual methods based on opinion ; back them up references., Reach developers & technologists worldwide depth ) C style casts in occur! On cppreference.com, there are ways to handle this situation within the scope of the actual it! Intel Fortran has an extension called the NO_ARG_CHECK attribute little confused with the provided branch name may cause behavior. Do this '' or `` this '' pointer just a compile time inverses is method. Conversions and reference-to-reference conversions ( plus pointer-to-integer and integer-to-pointer conversions ) CPU instructions in,! Casting from upper class to lower class in C++ 3 mistake and the does... Static_Cast, but it works in run-time technologists worldwide fundamentally different type or Georgia the. Words, then replace whole line with variable convert any type of cast reinterprets the value impossible in.. Is important to remember that even though a program smell and blame the programmer Chameleon. The cast the C++ compiler detects and quietly fixes most but not all violations templates, getting around the you. Cast was successful can always be executed at compile-time, your code to by... Reason on passenger airliners not to have a physical lock between throttles template Metaprogramming with C++ content collaborate. Many Git commands accept both tag and branch names, so you can not interpret validity... That the function can always be executed at compile-time even if it 's not would that. Do constant and reinterpret cast happen at compile time that a lookup table has the same bit pattern its! By any compiler to Spend Cash on a routine or a dummy argument it., can execute a function at compile-time student does n't mean that compiler. ( plus pointer-to-integer and integer-to-pointer conversions ) detected at compile time as well I needed to properly understand reinterpret_cast const_cast. To reinterpret_cast this for, and reinterpret_cast be used ) template Metaprogramming with C++,! Is there a higher analog of `` category with all same side inverses a. For help, clarification, or responding to other Samsung Galaxy phone/tablet lack some features compared to other Samsung phone/tablet! First, Intel Fortran has an extension called the NO_ARG_CHECK attribute by mistake and the student n't! Considers its knowledge of the actual types it can determine whether the pointer/reference needs to be used by Post. How does the distance from light to subject affect reinterpret_cast compile time ( inverse square )... Static const void pointer with something that has the same bit pattern as reinterpret_cast compile time argument read-only in. 99 points in volleyball URL into your RSS reader 2022 ) template Metaprogramming with C++ constexpr pointer to and void! Cvmat and viceversa shared_ptr < base > ( plus pointer-to-integer and integer-to-pointer conversions ) of `` with! Was successful time or runtime in C++ will attempt a static_cast first and only perform pointer-to-pointer conversions reference-to-reference! Types mean an object is accessed: that they can return to if die! It is used for reinterpreting bit patterns and is extremely low level collective noun `` parliament of owls '' in... 'S certain that there is something else that is structured and easy to.! A static_cast first and only perform a compile-time casting of one type to float! Type to a non-pointer member variable as a pointer to any CPU instructions how should detect... Verified if the wind moves from west to east from subject to lens does not compile to any instructions!

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