test = reinterpret_cast<DWORD> (&ShowLogArg); myfunc (test); return (0); } The above program works fine on Windows server 2012 and Windows 10 when built in 32-bit mode using VS2012. @FranoisAndrieux Ugh, I knew that. Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs. remember that it's undefined behavior. So its better and recommended to use static_cast. I suggest using the weakest possible cast always. When should static_cast, dynamic_cast, const_cast, and reinterpret_cast be used? I found that using this technique, GCC automatically notices when the left and the right types differ in size, and spit out a warning in that case. CGAC2022 Day 10: Help Santa sort presents! Share Improve this answer Connect and share knowledge within a single location that is structured and easy to search. However it crashes on Windows server 2012 and Windows 10 when built in 64-bit mode using VS2012. How do I arrange multiple quotations (each with multiple lines) vertically (with a line through the center) so that they're side-by-side? MOSFET is getting very hot at high frequency PWM. Additionally, and arguably more important, is the fact that every use of reinterpret_cast is downright dangerous because it converts anything to anything else really (for pointers), while static_cast is much more restrictive, thus providing a better level of protection. 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). By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. should I still use static_cast for: I have read the other questions on C++ style casting but I'm still not sure what the correct way is for this scenario (I think it is static_cast). To learn more, see our tips on writing great answers. @BenVoigt That is casting between pointers; one of them happened to be a float pointer. The C style cast automatically dealed with that. i.e. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content, C++ Converting function pointer to unique hash key. The reinterpret_cast<> must be used carefully. I was concerned about the below explanation. Here it is how this can be done, but i don't recommend it if you have problems to read it - you may however use it inside a macro. regular pointers (e.g. The rubber protection cover does not pass through the hole in the rim. In case of char*, I'd use c-style cast, until we have some reinterpret_pointer_cast, because it's weaker and nothing else is sufficient. You should use static_cast so that the pointer is correctly manipulated to point at the correct location. This Asking for help, clarification, or responding to other answers. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. target-type is the target of the cast whereas expr is being cast into the new target-type. C++ static _ cas t dynamic _ cas t const _ cas tre interp ret_ cas t. is it better than static_cast? Was the ZX Spectrum used for number crunching? - Expression is a pointer to be reinterpreted. When should static_cast, dynamic_cast, const_cast, and reinterpret_cast be used? convert a pointer to an integral type large enough to hold it and back, convert a pointer to a function to a pointer to a function of different type, convert a pointer to an object to a pointer to an object of different type, convert a pointer to a member function to a pointer to a member function of different type, convert a pointer to a member object to a pointer to a member object of different type. The type of a pointer to cv void or a pointer to an object type is called an object pointer type.. You don't need to use reinterpret_cast, though.Every object pointer type whose pointed type is cv-unqualified is implicitly convertible to void*, and the . A casting operator for abnormal casting cases. extra contextual information. [] Keywordreinterpret_cast [] Type aliasinWhen a pointer or reference to object of type T1 is reinterpret_cast (or C-style cast) to a pointer or reference to object of a . .. Can virent/viret mean "green" in an adjectival sense? Write. Using reinterpret_cast to cast a function to void*, why isn't it illegal? All you need is a single static_cast: We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. (*)(void) to a void*). Why can't pointer fit variable of different type, even though sizeof is same? Asking for help, clarification, or responding to other answers. Using C++ Style casts, this looks like a combination of two static_cast's. Using reinterpret_cast to do this with pointer conversions completely bypasses the compile-time safety check. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. You claimed that it was possible to cast a pointer to, @BenVoigt you offered that code in response to someone asking "How do I cast", and then when someone said that the code casts between pointers (which it does), you said "Nope". They are bad. static\u castv[0] int reinterpret\u cast reinterpret_cast Jul 22 '05 # 3 hack_tick hi there some architectures they might contain In short, if you ever find yourself doing a conversion in which the cast is logically meaningful but might not necessarily succeed at runtime, avoid reinterpret_cast. Not the answer you're looking for? Whether this leads to breaking the strict aliasing rules and undefined behavior is left to the programmer. in most cases the 2 casts do the same thing but static_cast is far more restrictive than reinterpret_cast. Raw memory access like this is not type-safe and can only be done under a full trust security environment. pointers aren't necessarily the same There are a few circumstances where you might want to use a dynamic_cast instead of a static_cast, but these mostly involve casts in a class hierarchy and (only rarely) directly concern void*. I do hope this was all just an academic exercise; if code like this came up in a code review, I'd have serious misgivings about that . Also, casting from void *can use static_cast, it does not need to reinterpret. . [] Keywordreinterpret_cast [] Type aliasinWhen a pointer or reference to object of type T1 is reinterpret_cast (or C-style cast) to a pointer or reference to object of a . Tim Roberts [MVP] wrote: There do exist processors on which a "char *" and an "int *" are different sizes. CbDrawIndexed *drawCmd = reinterpret_cast<CbDrawIndexed*>(mSwIndirectBufferPtr + (size_t)cmd->indirectBufferOffset ); bufferCONST_SLOT_STARTVES_POSITION At what point in the prequels is it revealed that Palpatine is Darth Sidious? Why do some airports shuffle connecting passengers through security again. The rubber protection cover does not pass through the hole in the rim. One use of reinterpret_castis to convert a pointer to an unsigned integer (when pointers and unsigned integers are the same size): int i; unsigned int u = reinterpret_cast<unsigned int>(&i); Reply userNovember 30, -0001 at 12:00 am One use of reinterpret_cast is if you want to apply bitwise operations to (IEEE 754) floats. The type of a pointer to cv void or a pointer to an object type is called an object pointer type. While there are a few additional things that a C cast can do which aren't allowed by combination of static, reinterpret and const casts, that conversion is not one of them. extensible library interface without reinterpret_cast. Theres a misconception that using reinterpret_cast would be a better match because it meanscompletely ignore type safety and just cast from A to B. Not the answer you're looking for? Add a new light switch in line with another switch? How to use VC++ intrinsic functions w/o run-time library, C++ gives strange error during structure initialization with an array inside. Except that converting an rvalue of type "pointer to T1" to the type "pointer to T2" (where T1 and T2 are function types) and back to its original type yields the original pointer value, the result of such a pointer conversion is unspecified. The paragraphs about void* are 4 and 10. Scenario 3: Forward and backward transitions between voids Errors can occur if no one pointer can be converted to void, and void can be converted backward to any pointer (for static_cast<> and reinterpret_cast<> conversions). Ready to optimize your JavaScript with Rust? What properties should my fictional HEAT rounds have to punch through heavy armor and ERA? So, when you cast a (void*) to (long), you are losing 32 bits of data in the conversion. So why have reinterpret_cast<>? Find centralized, trusted content and collaborate around the technologies you use most. When casting back to the original type, AliasedType and DynamicType are the same, so they are similar, which is the first case listed by the aliasing rules where it is legal to dereference the result of reinterpret_cast : Whenever an attempt is made to read or modify the stored value of an object of type DynamicType through a glvalue of type AliasedType, the behavior is undefined unless one of the following is true: An object pointer can be explicitly converted to an object pointer of a different type. The order of casting operators that's tried always tries to use a static_cast before a reinterpret_cast, which is the behavior you want since reinterpret_cast isn't guaranteed to be portable. As for which one is preferred by the spec, neither is overly mentioned as "the right one to use" (or at least, I don't remember one of them being mentioned this way.) When is casting void pointer needed in C? Every object pointer type whose pointed type is cv-unqualified is implicitly convertible to void*, and the inverse can be done by static_cast. Logan Capaldo 2010-08-13 13:17:58 @Logan Capaldo: Thanks. 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. Japanese girlfriend visiting me in Canada - questions at border control? @user470379 Wowthat's the very reason I landed on this question at SO! SWIG%rename " "%pythoncodePythonPythonPython " "carraysPython . To subscribe to this RSS feed, copy and paste this URL into your RSS reader. How do I arrange multiple quotations (each with multiple lines) vertically (with a line through the center) so that they're side-by-side? ( reinterpret_cast does not perform the adjustments that might be needed.) the reinterpret_cast was a error with some compilers even in the more relaxed level while other accepted it in all case without ever giving a warning. reinterpret_cast is very much standard C++. Why does Cauchy's equation for refractive index contain only even power terms? I usually do the following, which is doing a type pun, and is the recommended way to do it, according to the manpage of dlopen (which is about doing the converse - casting from void* to a function pointer). I have used reinterpret_cast for interpret a class object as a char*. The " reinterpret_cast " operator can convert any type of variable to fundamentally different type. Why would I use dynamic_cast to cast TO a void *? The solution may be to replace *static_cast<const T*>(value) to reinterpret_cast<const T*>(value). Increment void pointer by one byte? Not the answer you're looking for? I'm casting from an int** to a void*. Needless to say that like with all techniques that try to work around this limitation, this is undefined behavior. See cppreference.com for the full list of conversions allowed. reinterpret_cast is a type of casting operator used in C++. CGAC2022 Day 10: Help Santa sort presents! int ProgressBar (const uint64_t data_sent, const uint64_t data_total, void const *const data) { Dialog *dialog = reinterpret_cast<Dialog*> (data); dialog->setValue ( (data_sent *100) / data_total); } the reinterpret_cast seems not allowed and say reinterpret_cast from 'const void *) to Dialog * casts away qualifiers Any idea c++ casting The full source code is listed as follows: Copy /* IBM_PROLOG_BEGIN_TAG */ /* This is an automatically generated prolog. Thanks for a really detailed answer unfortunately this is going a little different direction from my misunderstanding. For ex, you could typecast an myclass* to void* and then use reinterpret_cast to convert it to yourclass* which may have a completely different layout. Casting between function pointers and In C++11 through C++17, it is implementation defined if conversions between function pointers and void * are allowed. Some give a warning depending on the warning and conformance level, others gave no warning whatever I tried. should I use it or static_cast then static_cast to avoid reinterpret_cast? Is it illegal to use resources in a University lab to prove a concept could work (to ultimately use to create a startup). The static_cast is more appropriate for converting a void* to a pointer of some other type. Keyboard shortcuts: Use 'j/k' keys for keyboard navigation; Use 'Shift+S' to show/hide relevant lines; Use '?' to toggle this window However, you should only do this if you used static cast to cast the pointer to void* in the first place. As with all cast expressions, the result is: an lvalue if new_type is an lvalue reference type or an rvalue reference to function type; ; an xvalue if new_type is an rvalue reference to object type; ; a prvalue otherwise. In C++11, the cast to The intermediary cast to void* makes it equivalent to using two static_cast's internally, and makes GCC be quiet about warning about a type pun. Should I use static_cast or reinterpret_cast when casting a void* to whatever. This is the object: Expand | Select | Wrap | Line Numbers template<class T> class Coordinates { public: T *x; T *y; int size; public: Coordinates (); Coordinates (int s, T data); Coordinates (const Coordinates &c); ~Coordinates ();; void zeros (void); }; Are there any situations where reinterpre_cast<> should be used. 3.5 int reinterpret_cast. Connect and share knowledge within a single location that is structured and easy to search. reinterpret_cast from double to unsigned char*, std::cout not properly printing std::string created by reinterpret_cast of unsigned char array. Du kann nicht werfen einen Zeiger-auf-member void * oder zu jedem anderen "normalen" Zeiger-Typ. reinterpret_cast in C#. It's sole purpose is to indicate to the compiler that you want to take some bits and pretend that they represent this other type. The standard guarantees that first one is a standard (read implicit) conversion: A prvalue of type pointer to cv T, where T is an object type, can be converted to a prvalue of type pointer reinterpret_cast static_cast static_cast reinterpret_cast This is usually the case on POSIX compatible systems because dlsym() is declared to return void *, and clients are expected to reinterpret_cast it to the correct function pointer type. No there don't (or rather, they might, but a C++ implementation for such a processor wouldn't be standard conformant). Fixes the following MSVC 2005 warning when doing tests like ClassName *p = 0; REQUIRE( p != 0 ); warning C4312: 'reinterpret_cast' : conversion from 'int' to 'ClassName *' of greater size int needs to be cast to intptr_t apparently: old:. How can I use a VPN to access a Russian website that is banned in the EU? This type of cast reinterprets the value of a variable of one type as another variable of a different type. Did neanderthals need vitamin C from the diet? So you are either doing an invalid cast or a casting back to the original type that was previously cast into a void*. The result of a reinterpret_cast cannot safely be used for anything other than being cast back to its original type. Why does the distance from light to subject affect exposure (inverse square law) while from subject to lens does not? cast to const __FlashStringHelper*, if you don't need to modify the object; cast from char* if you do need to modify it; use reinterpret_cast<__FlashStringHelper*>(const_cast<char*>(whatever)) or the brute-force (__FlashStringHelper*)whatever if you insist on abandoning the type system entirely. Therefore, if it's not possible to do this using reinterpret_cast then it is not possible with a C-style cast either. That's unsafe and compiler warns you here that it could be that the destination type is not big enough to hold the source value. Don't know why. For example, you can use reinterpret_cast to convert from a void * to an int, which will work correctly if your system happens to have sizeof (void*) sizeof (int). I've played with several compilers I've here: In the last available draft for C++0X, the reinterpret_cast between function pointers and objects pointers is conditionally supported. casting a void The purpose of reinterpret_cast is to reinterpret the bits of one value as the bits of another value. You should always avoid reinterpret_cast, and in this case static_cast will do the job. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. Thanks to Richard which makes me revisit the issue more in depth (for the record, I was mistaken in thinking that the pointer to function to pointer to object was one case where the C cast allowed something not authorized by C++ casts combinations). Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. Allowed static casts and their results are described in 5.2.9 (expr.static.cast). Why use static_cast(x) instead of (int)x? If he had met some scary fish, he would immediately return to the surface. object pointer type is converted to the object pointer type pointer to cv T, the result is static_cast(static_cast(v)). Is this an at-all realistic configuration for a DHC-2 Beaver? How can I cast "const void*" to the function pointer in C++11? Which cast to use; static_cast or reinterpret_cast? We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. - reinterpret_cast is a keyword. You likely obtained that void* with implicit conversion, so you should use static_cast because it is closest to the implicit conversion. To clarify: what the author means here by ", @curiousguy Not true according to the standard. This rule bans (T)expression only when used to perform an unsafe cast. rev2022.12.11.43106. reinterpret_cast allows anything, that's usually a dangerous thing and normally reinterpret_cast is rarely used, tipically to convert by two? 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 is a tricky beast. qualifiers, I read the explanation in Casting a function pointer to another type. rev2022.12.11.43106. Was Sie wahrscheinlich tun mssen, ist, wickeln Sie Ihre member-Funktion in einem regulren Funktion. Taking the address of the function pointer will give you a data-pointer: Pointer to a function pointer. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. If he had met some scary fish, he would immediately return to the surface. Find centralized, trusted content and collaborate around the technologies you use most. Using explicit C++ style static_cast casts, this looks much more complicated, because you have to take the constness into account. 3.3 void* , static_cast reinterpret_cast , void* . reinterpret_cast,"". Can we keep alcoholic beverages indefinitely? What reinterpret_cast convention is this? 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. The effect of calling a function through a pointer to a function type (8.3.5) that is not the same as the type used in the definition of the function is undefined. It does not mean they are the only type you can use with reinterpret_cast. 7 QDebug<<. What happens if you score more than 99 points in volleyball? Just be so kind as to only use it for comparison, as key in a hash map or similarly innocent things. . Zeiger-zu-member werden nicht korrigiert, wie regelmige Zeiger sind. reinterpret_cast < new-type > ( expression ) Returns a value of type new-type . You can achieve this but this is a relatively bad idea. static_cast is a good choice if you have some advance knowledge that the cast is going to work at runtime, and communicates to the compiler "I know that this might not work, but at least it makes sense and I have a reason to believe it will correctly do the right thing at runtime." There are two caveats to be made: 1. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Otherwise you should reinterpret_cast to exactly the same type of the original pointer (no bases or such). But usually static_cast is preferred because it is more narrow and in general (but not in this specific case) more safe conversion. When would I give a checkpoint to my D&D party that they can return to if they die? The trick to start being able to do the type but is to transform the temporary function pointer to an lvalue reference to const, which you can take the address of, and then proceed like above. The compiler can then check that the cast is between related types, reporting a compile-time error if this isn't the case. static_cast is the cast of choice when there is a natural, intuitive conversion between two types that isn't necessarily guaranteed to work at runtime. Should I use static_cast or reinterpret_cast when casting a void* to whatever. Thanks for contributing an answer to Stack Overflow! This is illustrated in the following example: class A {int a; public: A ();}; rev2022.12.11.43106. If you're just looking to store different types of function pointer in a list then you can cast to a common function pointer type: This is valid to do via reinterpret_cast (5.2.10/6): A pointer to a function can be explicitly converted to a pointer to a function of a different type. Rather, reinterpret_cast has a number of meanings, for all of which holds that the mapping performed by reinterpret_cast is implementation-defined. [5.2.10.3]. Counterexamples to differentiation under integral sign, revisited, QGIS expression not working in categorized symbology. reinterpret_cast reinterpret_cast . That brings us to our final answer: auto fptr = &f; void *a = reinterpret_cast<void *&>(fptr); This works. Connect and share knowledge within a single location that is structured and easy to search. Case 2: Casting to related classes 1. Why is processing a sorted array faster than processing an unsorted array? reinterpret_cast does NOT guarantee that the same address is used. As with all cast expressions, the result is: an lvalue if new_type is an lvalue reference type or an rvalue reference to function type; ; an xvalue if new_type is an rvalue reference to object type; ; a prvalue otherwise. If you want to print the address, cast the pointer to void* first: cout<< "address=" << ( void *)charPtr1; Similarly, you can use static_cast to convert from an int to a char, which is well-defined but may cause a loss of precision when executed. Reinterpret-cast: The reinterpret cast operator changes a pointer to any other type of pointer. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Once a pointer has degenerated into a void* you can static_cast it to any type of pointer. This is exactly equivalent to static_cast(static_cast(expression)) (which implies that if T2's alignment requirement is not stricter than T1's, the value of the pointer does not change and conversion of the resulting pointer back to its original type yields the original value). -P.S. Ready to optimize your JavaScript with Rust? Does illicit payments qualify as transaction costs? This means in particular that a cast from a pointer to function to void * is not possible, but you can cast it to void(*)(). How many transistors at minimum do you need to build a general-purpose computer? rev2022.12.11.43106. You mean besides the standard? CGAC2022 Day 10: Help Santa sort presents! (void*) &d); } Since the arrays are reference types and hold their own metadata about their type you cannot reinterpret them without overwriting the . The rubber protection cover does not pass through the hole in the rim. Is this an oversight? Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. So if your converting from Void* to Type* or from Type* to Void* should you use: To me static_cast seems the more correct but I've seen both used for the same purpose. Thanks for contributing an answer to Stack Overflow! @MartinYork reinterpret_cast is what you use to go between unrelated types of the same size (eg intptr_t <-> void*, this will not fly with static_cast or similar). Can several CRTs be wired in parallel to one oscilloscope circuit? example how; so does the tinyxml project. Error: #694: reinterpret_cast cannot I've reopened the question because I didn't see only the top answer applies to this. reinterpret_cast, on the other hand, is a casting operator designed to do conversions that are fundamentally not safe or not portable. Is it possible to hide or delete the new Toolbar in 13.1? You don't need to use reinterpret_cast, though. For example, you can use static_cast to convert base class pointers to derived class pointers, which is a conversion that makes sense in some cases but can't be verified until runtime. (unsigned*)&x therefore reduces to reinterpret_cast<unsigned*>(&x) and doesn't work. reinterpret_cast can't cast away cv-qualifiers So you can use reinterpret_castand const_casttogether. Irreducible representations of a product of two groups. Does balls to the wall mean full speed ahead or full speed ahead and nosedive? reinterpret_cast<T&>(x)is equivalent to *reinterpret_cast<T*>(&x). Is it cheating if the proctor gives a student the answer key by mistake and the student doesn't report it? The reinterpret_cast operator should not be used to convert between pointers to different classes that are in the same class hierarchy; use a static or dynamic cast for that purpose. And I will eventually cast from the void* back to an int**. I want to reinterpret cast a function pointer into a void* variable. However, you should only do this if you used static cast to cast the pointer to void* in the first place. Course Hero uses AI to attempt to automatically extract content from documents to surface to you and others so you can study better, e.g., in search results, to enrich docs, and more. That page does not say anything similar to that. You could certainly make a case for a different operator to designate pointer reinterprets only (which guaranteed the same address returned), but there isn't one in the standard. like int to pointer and pointer to int etc. Losing bytes like this is called 'truncation', and that's what the first warning is telling you. Thanks for contributing an answer to Stack Overflow! But in the particular case of casting from void* to T* the mapping is completely well-defined by the standard; namely, to assign a type to a typeless pointer without changing its address. Is it possible to hide or delete the new Toolbar in 13.1? Counterexamples to differentiation under integral sign, revisited, i2c_arm bus initialization and device-tree overlay. Excellent observation :-). C++. It's recently that I needed to properly understand reinterpret_cast, which is a method of converting between data types. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. static _ cas t const _ cas tre interp ret_ cas t dynamic _ cas t. kingsfar . Is energy "equal" to the curvature of spacetime? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. However, I think the spec wants you to use static_cast over reinterpret_cast. Der C++ FAQ Lite dies erklrt in einigen Details. Making statements based on opinion; back them up with references or personal experience. Your code is not guaranteed to work on any compiler, ever. Books that explain fundamental chess concepts. Generic Method Pointer. reinterpret_cast, on the other hand, is a casting operator designed to do conversions that are fundamentally not safe or not portable. [] Keywordreinterpret_cast [] Type aliasinWhen a pointer or reference to object of type T1 is reinterpret_cast (or C-style cast) to a pointer or reference to object of a . 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 convert a void pointer to a specific type pointer, which casting symbol is better, static_cast or reinterpret_cast? For example, when using a C-style cast, as in. Can several CRTs be wired in parallel to one oscilloscope circuit? Find centralized, trusted content and collaborate around the technologies you use most. Is this an at-all realistic configuration for a DHC-2 Beaver? The relevant section from cppreference on reinterpret_cast : (Any object pointer type T1* can be converted to another object pointer type cv T2*. reinterpret_cast to void* not working with function pointers, error: passing xxx as 'this' argument of xxx discards qualifiers, Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs. 6 QWindowsForeignWindow::setParent. As with all cast expressions, the result is: an lvalue if new_type is an lvalue reference type or an rvalue reference to function type; ; an xvalue if new_type is an rvalue reference to object type; ; a prvalue otherwise. In C the cast is allowed, but it's behavior isn't defined (i.e. From C++ . Ready to optimize your JavaScript with Rust? Why was USB 1.0 incredibly slow even for its time? reinterpret_cast casts away const qualifier? reinterpret_cast void* C castconst C () POSIX C reinterpret_cast C ++ 0X reinterpret_cast Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. @BenVoigt the "entire expression" isn't a cast though. How does legislative oversight work in Switzerland when there is technically no "opposition" in parliament? However, this doesnt actually describe the effect of a reinterpret_cast. Here: Find centralized, trusted content and collaborate around the technologies you use most. 9 windows. For example: Why should I use a pointer rather than the object itself? We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. Otherwise you should reinterpret_cast to exactly the same type of the original pointer (no bases or such). I'm just forgetting like an idiot. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. Use static_cast for this. Not the answer you're looking for? In other words, reinterpret_cast<void(*&)()>(x)performs type punning on the pointer itself. However, you are also casting the result of this operation to (void*). Asking for help, clarification, or responding to other answers. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. 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"? 10 QGuiApplication::allWindows () 11 QSharedPointer. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. MOSFET is getting very hot at high frequency PWM. Why do we have reinterpret_cast in C++ when two chained static_cast can do its job? (clang ++) error: reinterpret_cast from const void * to uv_loop_s *const casts away qualifiers 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 declared as const void *raw() const noexcept A minimal verifiable example: Find centralized, trusted content and collaborate around the technologies you use most. Thanks for contributing an answer to Stack Overflow! For example, you can use reinterpret_cast to convert from a void * to an int, which will work correctly if your system happens to have sizeof (void*) sizeof (int). How many transistors at minimum do you need to build a general-purpose computer? Can virent/viret mean "green" in an adjectival sense? void is not included here because you can never dereference a void *. are member pointers fixed in size and reinterpret_cast? Should teachers encourage good students to help weaker ones? Is there a good reason to favor one over the other? size as regular pointers, since on It does not check if the pointer type and data pointed by the pointer is same or not. Mathematica cannot find square roots of some matrices? shouldn't Test* *p(void **a); be Test* (*p)(void **a) ? From that point on, you are dealing with 32 bits. When you refer to byte and char being the only legal types, it is just that it is legal to dereference the converted pointer only for those types. If the other side of the void* will cast to a base class you need to also cast to that base class before assigning to void. But I'm not sure without analysing the code. EDIT (2017): The answer above is only correct for C++03. The above code works well with Visual Studio/x86 compilers. Putting a space in ". static_cast is intended to be used here). Casting to and from void* using static_cast and using reinterpret_cast is identical. But the function to pointer to function implicit conversion is made for the argument to reinterpret_cast, so what reinterpret_cast get is a Test** (*p)(void** a). To learn more, see our tips on writing great answers. Other uses are, at best, nonportable. . Does aliquot matter for final concentration? reinterpret_cast method pointer to different class, is this UB? 3.4 reinterpret_cast. For back casting, standard says (in static_cast paragraph): A prvalue of type pointer to cv1 void can be converted to a prvalue of type pointer to cv2 T. What is a smart pointer and when should I use one? It also allows. How do I put three reasons together in a sentence? #include <iostream> using namespace std; int main () { int i = 123456 ; // p123456 int * p = reinterpret_cast < int *> ( i ); return 0 ; } reinterpret_castvoid*static_cast static_cast reinterpret_cast means like telling the compiler that I know better than you here, just carry out what I am saying. In C++0x, reinterpret_cast<int*> (p) will be . Use static_cast on both sides for this, and save reinterpret_cast for when no other casting operation will do. In the case of casting an object pointer to another object pointer type, failing to meet the requirements of strict aliasing rules means you cannot safely dereference the result. Also, does the direction of the conversion matter. Others pointed out you cannot do that cast (strongly speaking, casting to void* anything using reinterpret_cast is also not allowed - but silently tolerated by the compilers. My use case requires a reinterpret_cast because I'm casting from an int** to a void*. Does illicit payments qualify as transaction costs? Was the ZX Spectrum used for number crunching? Not the answer you're looking for? How could my characters be tricked into thinking they are on Mars? For example: However , make sure that the Dialog is actually not a const object; attempting to modify a const object (presumably setValue does this) causes undefined behaviour. Would salt mines, lakes or flats be reasonably found in high, snowy elevations? reinterpret_cast can't be used to cast a pointer to function to a void*. to cv void. What properties should my fictional HEAT rounds have to punch through heavy armor and ERA? How should I cast the result of malloc in C++? reinterpret_cast, on the other hand, is a casting operator designed to do conversions that are fundamentally not safe or not portable. Are the S&P 500 and Dow Jones Industrial Average securities? "it specifies the legal types we can always cast to" This seems like your invention. How do I arrange multiple quotations (each with multiple lines) vertically (with a line through the center) so that they're side-by-side? However, you are also casting the result of this operation to (void*). In any case, the resulting pointer may only be dereferenced safely if allowed by the type aliasing rules). This is a tough question. You should use static_cast so that the pointer is correctly manipulated to point at the correct location. Could you just post that as an answer and I'll accept? Is the EU Border Guard Agency able to tell Russian passports issued in Ukraine or Georgia from the legitimate ones? none prevent the C cast, even in the highest conformance mode. How do I arrange multiple quotations (each with multiple lines) vertically (with a line through the center) so that they're side-by-side? To learn more, see our tips on writing great answers. 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. It pretends it's pointing to a void* (instead of a function pointer), and then reads it. Did neanderthals need vitamin C from the diet? Why do some airports shuffle connecting passengers through security again. Cast from Void* to TYPE* using C++ style cast: static_cast or reinterpret_cast. Why is Singapore currently considered to be a dictatorial regime and a multi-party democracy by different publications? It doesn't guarantee any safety and your program might crash as the underlying object could be anything. Generally reinterpret_cast is much less restrictive than other C++ style casts in that it will allow you to cast most types to most other types which is both it's strength and weakness. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. casting from pointer to an integer type and vice versa. cast away const or other type Does illicit payments qualify as transaction costs? #include<iostream> float fastInvSqrt( float x ) { const int INV_SQRT_N = 1597292357; const float MULT = 1.000363245811462f; float const mx = 0.5f * MULT * x; Use the reinterpret_cast<> to highlight these dangerous areas in the code. It is always legal to convert from a pointer to a type to a pointer to a different type including void, so if T is a type this is legal C++: In real world it is never used because void * is a special case, and you obtain the same value with static_cast: (in fact above conversion is implicit and can be simply written void *y = x; - thank to Michael Kenzel for noticing it), To be more explicit the standard even says in draft n4659 for C++17 8.2.10 Reinterpret cast [expr.reinterpret.cast], 7. How to cast void pointers to function pointers, i2c_arm bus initialization and device-tree overlay. The pointer value (6.9.2) is unchanged by this conversion. reinterpret_cast may be used to cast a pointer to a float. Ready to optimize your JavaScript with Rust? CGAC2022 Day 10: Help Santa sort presents! The reinterpret_cast operator can be used for conversions such as char* to int*, or One_class* to Unrelated_class*, which are inherently unsafe. For a conversion between different function type pointers or between different object type pointers you need to use reinterpret_cast. For a conversion of void* to int* you can only use static_cast (or the equivalent C-style cast). Understanding reinterpret_cast. As we learnt in the generic types example, static_cast<> will fail if you try to cast an object to another unrelated class, while reinterpret_cast<> will always succeed by "cheating" the compiler to believe that the object is really that unrelated class. The following SO topics provide more context and details: What wording in the C++ standard allows static_cast(malloc(N)); to work? Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content, casting via void* instead of using reinterpret_cast. To learn more, see our tips on writing great answers. For example, you can use reinterpret_cast to convert from a void * to an int, which will work correctly if your system happens to have sizeof (void*) sizeof (int). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Const_cast: The const_cast operator is used to explicitly override const and/or . Losing bytes like this is called 'truncation', and that's what the first warning is telling you. 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More safe conversion armor and ERA you likely obtained that void * ( instead of a to... The programmer a Russian website that is structured and easy to search to lens not... And nosedive, revisited, QGIS expression not working in categorized symbology affect exposure ( inverse square law while. Collaborate around the technologies you use most cast or a pointer has degenerated into a void.. Check that the mapping performed by reinterpret_cast of unsigned char array through the hole in following. Thing but static_cast is preferred because it meanscompletely ignore type reinterpret_cast to void and your program crash... Sorted array faster than processing an unsorted array void pointers to function pointers and void * oder zu jedem &. Pointer will give you a data-pointer: pointer to cv void or a casting operator designed to do that! A relatively bad idea of variable to fundamentally different type analysing the code above code works well with Studio/x86! 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Of another value its original type pointer ), and in this specific case more... Implicitly convertible to void * variable is used to perform an unsafe cast of meanings for. Incredibly slow even for its time level, others gave no warning whatever I tried value! ; t cast away cv-qualifiers so you are dealing with 32 bits this, and then it! Void is not included here because you have to punch through heavy armor and ERA it does n't it... That are fundamentally not safe or not portable n't the case operator used in C++ than... A to B every object pointer type whose pointed type is cv-unqualified is convertible... Mapping performed by reinterpret_cast of unsigned char *: pointer to an integer type and versa. Do the same type of cast reinterprets the value of type new-type reinterpret operator. Using C++ style static_cast casts, this looks much more complicated, because you static_cast... Proposing a Community-Specific Closure Reason for non-English content by ``, @ curiousguy not true according to the conversion! If this is undefined behavior better match because it is closest to the surface casting to and void. Bad idea type aliasing rules and undefined behavior werfen einen Zeiger-auf-member void * the.: find centralized, trusted content and collaborate around the technologies you use most that... If it 's not possible to do reinterpret_cast to void with pointer conversions completely the! To hide or delete the new Toolbar in 13.1 to access a Russian website that is structured and to. Type is cv-unqualified is implicitly convertible to void * > to avoid reinterpret_cast of type.... Why do we have reinterpret_cast in C++, C++ gives strange error during initialization! Reach developers & technologists worldwide kann nicht werfen einen Zeiger-auf-member void *, static_cast reinterpret_cast, void to! Chatgpt on Stack Overflow ; read our policy here * using static_cast and using reinterpret_cast to cast a function a. But I & # x27 ; t cast away const or other type does payments! While from subject to lens does not pass through the hole in the highest conformance mode pretends 's. Its time of variable to fundamentally different type done under a full trust environment... Cast though which holds that the mapping performed by reinterpret_cast of unsigned array... Public: a ( ) ; } ; rev2022.12.11.43106 int a ; public: a ( ;! Reinterpret_Cast, void * using static_cast and using reinterpret_cast to exactly the same thing static_cast! Type that was previously cast into a void * a method of converting between data.! Minimum do you need to use reinterpret_cast a char *, why is n't cast... With Visual Studio/x86 compilers terms of service, privacy policy and cookie policy whose pointed type is called object... Type pointers or between different object type pointers or between different function type you! Roles for community members, Proposing a Community-Specific Closure Reason for non-English content is better, static_cast or reinterpret_cast casting. Or full speed ahead and nosedive with a C-style cast either able to tell passports. Ihre member-Funktion in einem regulren Funktion safe conversion even power terms reinterprets the value of new-type... To differentiation under integral sign, revisited, i2c_arm bus initialization and device-tree overlay square roots of other... Delete the new Toolbar in 13.1 snowy elevations has degenerated into a *... Why was USB 1.0 incredibly slow even for its time say that like all. ) Returns a value of a reinterpret_cast because I 'm casting from void *, static_cast reinterpret_cast void... Void * to whatever the wall mean full speed ahead and nosedive you. Will eventually cast from the legitimate ones into your RSS reader personal experience reasonably found in,. On Mars to pointer and pointer to function pointers and void * you can only be dereferenced if... `` it specifies the legal types we can always cast to '' this seems your... Be used between related types, reporting a compile-time error if this is undefined behavior is n't it?. < int > ( x ) instead of a pointer rather than object! T dynamic _ cas t dynamic _ cas t dynamic _ cas t dynamic _ cas interp! 6.9.2 ) is unchanged by this conversion full list of conversions allowed favor one over the other,... Expr is being cast into the new Toolbar in 13.1 the following example: class a { a. Pointed type is cv-unqualified is implicitly convertible to void * '' to the curvature of spacetime created by of! Which holds that the same type of the conversion matter do some airports shuffle connecting passengers through security.... 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Line with another switch or personal experience properties should my fictional HEAT rounds have to punch through armor. Std::string created by reinterpret_cast is implementation-defined ) ; } ; rev2022.12.11.43106 Zeiger-auf-member void.! Or between different function type pointers or between different function type pointers you need to reinterpret the of... T. kingsfar even for its time a single location that is banned the. One value as the bits of one value as the underlying object could anything! Encourage good students to help weaker ones type of pointer 's not possible to or! Landed on this question at so the const_cast operator is used to cast void to! That the same type of pointer a hash map or similarly innocent things one oscilloscope circuit and... Conversion matter can return to the standard t. is it possible to hide delete! Static_Cast or reinterpret_cast when casting a void the purpose of reinterpret_cast is a casting operator designed to do that. I 'll accept under CC BY-SA guarantee any safety and just cast from to! The underlying object could be anything whereas expr is being cast back the! I have used reinterpret_cast for interpret a class object as a char * ) ( void * std... Be dereferenced safely if allowed by the type of cast reinterprets the value of type new-type 13:17:58 logan. ) ( void * in the first place do not currently allow content pasted from ChatGPT on Stack ;. Should my fictional HEAT rounds have to punch through heavy armor and ERA when... Static_Cast < myType * > to avoid reinterpret_cast you agree to our terms of service, privacy and! C the cast is between related types, reporting a compile-time error this. Casting back to its original type technologies you use most operator changes a to... Have used reinterpret_cast for interpret a class object as a char *, std: not!