reinterpret_cast conversion

These bullets were eventually removed via CWG2051. @litb This is an interesting comment. Note that many C++ compilers relax this rule, as a non-standard language extension, to allow wrong-type access through the inactive member of a union (such access is not undefined in C). You can freely cast any type, it just might not do what you hope it does, and might not be guaranteed to do anything at all. Reinterpret_cast in c++ allows any pointer to be converted into any other pointer type. Appropriate translation of "puer territus pedes nudos aspicit"? . The following does not violate strict aliasing, and is OK provided that the bit pattern in randomUintNumber is a valid representation of a value of long long: So on implementations where int64_t and uint64_t are typedefs for long long and unsigned long long, then my reinterpret_cast is OK. And as with the implementation-defined conversion of out-of-range values to signed types, you would expect that the sensible thing for implementations to do is to make them corresponding signed/unsigned types. Why did the Council of Elrond debate hiding or sending the Ring away, if Sauron wins eventually in that scenario? If you need to work around that, and you don't trust the implementation to be sensible about converting out-of-range unsigned values to signed types, then something like this: Now, I'm in favour of writing truly portable code where possible, but even so I think this verges on paranoia. Add a new light switch in line with another switch? I checked the assembly code produced by VC2008 and it omits the same code. Let's confirm the output above makes sense, anyway. Differing cases of compile time error and undefined behavior: If you do eg float x; return (int)(x)+1; you should see it emit the proper fld/fistp sequence. Should I give a brutally honest feedback on course evaluations? In your specific case, all options yield the same result. The conversion from const char* as returned by c_str() to std . It also permits any integral type to be converted into any pointer type and vice versa. A small bolt/nut came off my mtn bike while washing it, can someone help me identify it? Why I can't compile this code? Don't make your code unprovoked complexer. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Type aliasing . It does not check if the pointer type and data pointed by the pointer is same or not. In this case the standard treats reinterpret_cast as a static_cast to void* first and then a static_cast to the desination type. What is the difference between const int*, const int * const, and int const *? Where do I find the current C or C++ standard documents? That means that when it acts like a reinterpret_cast, it has the exact same problems as a reinterpret_cast. From cppreference.com . http://en.wikipedia.org/wiki/Single_precision_floating-point_format#IEEE_754_single-precision_binary_floating-point_format:_binary32. How do I convert a String to an int in Java? So like the static_cast and the implicit conversion, you expect it to work in any sensible implementation but it is not actually guaranteed. The purpose of strict aliasing and related rules is to enable type-based alias analysis, which would be decimated if a program can validly create a situation where two pointers to unrelated types (e.g., an int* and a float*) could simultaneously exist and both can be used to load or store the same memory (see this email on SG12 reflector). Why is it so much harder to run on a treadmill when not holding the handlebars? Add a new light switch in line with another switch? Connect and share knowledge within a single location that is structured and easy to search. Conversely, a C-style cast (as in (int)42.0) is much harder to find reliably by searching To answer the other part of your question, yes, reinterpret_cast is implementation-defined. Syntax : As mentioned in the previous section, implicit type conversion is safe, and explicit type conversion is risky. 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.. Only the following conversions can be done with reinterpret_cast . Would it be possible, given current technology, ten years, and an infinite amount of money, to construct a 7,000 foot (2200 meter) aircraft carrier? It can cast integer and floating point types into each other. However, this is not guaranteed for a function pointer. Why are elementwise additions much faster in separate loops than in a combined loop? What's the difference between undefined and implementation defined? [] ExplanatioUnlike static_cast, but like const_cast, the reinterpret_cast expression does not compile to any CPU instructions. Don't conclude from the answers that (type)expression in C++ is equivalent to a reinterpret_cast. Why should someone do this? Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. @edA-qamort-ora-y: Yes it is 5.2.10/4 "A pointer can be explicitly converted to any integral type. 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. Is Energy "equal" to the curvature of Space-Time? If they were pointers, maybe it would matter that they pointed to things of the same size, but they're not pointers. Does balls to the wall mean full speed ahead or full speed ahead and nosedive? . C-style casts just look like type names in parenthesis: Obviously there are better uses for casts than this, but that's the basic syntax. Use static_cast in these cases. @curiousguy [expr.reinterpret.cast.11], although that says it needs to be cast to a reference. You can freely cast pointer types in C as you would any other type. is a great article, describing the problem and its solution (maybe skip the lengthy part "Now, to the Rule-Book" ;) ). To learn more, see our tips on writing great answers. At what point in the prequels is it revealed that Palpatine is Darth Sidious? Other uses are, at best, nonportable. 1980s short story - disease of self absorption. We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. This is used a lot when doing binary protocols where data structures often have the same header information and allows you to convert types which have the same layout, but differ in C++ class structure. 1)An expression of integral, enumeration, pointer, or pointer-to-member type can be converted to its own type. Returns a value of type new_type.. mathk 28 Note that the (type)exression equivalent of C can do much more than reinterpret_cast in C++ (well, after all, they are two different languages - so we can't expect much anyway). 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. Sed based on 2 words, then replace whole line with variable. Asking for help, clarification, or responding to other answers. When you convert for example int (12) to unsigned float (12.0f) your processor needs to invoke some calculations as both numbers has different bit representation. Both are valid statements, and both will compile only because of the cast. This page was last modified on 29 June 2022, at 23:21. C++11 introduced a standardized memory model. So it's really a very platform specific for conversions like: It is intended to be unsurprising to those who know the addressing structure It is not possible to do with c-style casts. That part is implementation-defined. reinterpret_cast < new-type > ( expression ) Returns a value of type new-type . It recommends memcpy and argues, that compiler optimization will skip the copying anyway. How to connect 2 VMware instance running on same Linux host machine via emulated ethernet cable (accessible via mac address)? How to smoothen the round border of a created buffer to make it look more natural? And how is it going to affect C++ programming? reinterpret_cast. It's misleading. Iteration statements (loops) for: range-for (C++11)while: do-while Demonstrates some uses of reinterpret_cast: The following behavior-changing defect reports were applied retroactively to previously published C++ standards. A cast between signed and unsigned integral types does, and so does a cast from. So it is implementation-specific whether or not this code violates strict aliasing. rev2022.12.9.43105. Better way to check if an element only exists in one array. Improve INSERT-per-second performance of SQLite, Obtain closed paths using Tikz random decoration on circles. This page has been accessed 1,191,892 times. Even if randomUintNumber is a compile-time constant, unfortunately here randomIntNumber is not a compile-time constant. Not the answer you're looking for? To learn more, see our tips on writing great answers. Unlike static_cast, but like const_cast, the reinterpret_cast expression does not compile to any CPU instructions. In C, aggregate copy and assignment access the aggregate object as a whole. When would I give a checkpoint to my D&D party that they can return to if they die? Better way to check if an element only exists in one array. How did muzzle-loaded rifled artillery solve the problems of the hand-held rifle? Except that converting a prvalue 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. We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. For those cases, you can use reinterpret_cast. Of course, if you want something to happen other than compiling, you'd use '='. 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). The resulting value is the same as the value of expression. For example, dk.cpp: In function 'int main()': But if you compile using a different compiler, or targeting a difference CPU, it might do something else (which, again, has to be documented). Find centralized, trusted content and collaborate around the technologies you use most. Only the following conversions can be done with reinterpret_cast, except when such conversions would cast away constness or volatility . Note that this is probably not guaranteed to work by the C standard. So yes, if you rely on the intermediate value, your code is non-portable. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Whenever an attempt is made to read or modify the stored value of an object of type DynamicType through a glvalue of type . Both reinterpret_cast and c-style casts are implementation defined and they do almost the same thing. No If you want randomIntNumber to have the same bit-pattern as randomUintNumber, then you can do this: Since int64_t is guaranteed to use two's complement representation, you would hope that the implementation defines static_cast to have the same result as this for out-of-range values of uint64_t. The resulting value is the same as the value of expression. Only the following conversions can be done with reinterpret_cast, except when such conversions would cast away constness or volatility. If you want to be portable, you have to do the full round-trip. both types have the same bit length, isn't it what reinterpret_cast is intended for? did anything serious ever run on the speccy? Would the implementation-defined result differ if i run it on a different compiler or on the same one again? It can do many different things, and it's not always clear from reading the code which type of cast will be invoked (it might behave like a, Consequently, changing the surrounding code might change the behaviour of the cast, It's hard to find when reading or searching the code -. That's usually all well and good, but when you want to cast a double to a uint64_t, sometimes you want the value and sometimes you want the bits. From [expr.reinterpret.cast].6 (emphasis mine):. [.] Interactive code here. error C2440: 'reinterpret_cast' : cannot convert from 'const uint64_t' What is the C equivalent for reinterpret_cast? Did neanderthals need vitamin C from the diet? 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.. Only the following conversions can be done with reintepret_cast . isn't it what reinterpret_cast is intended for? they are both arrays of the same size or at least one of them is array of unknown bound, and the array element types are similar. The exponent is 0. The paragraph defining the strict aliasing rule in the standard used to contain two additional bullets partially inherited from C: These bullets describe situations that cannot arise in C++ and therefore are omitted from the discussion above. Asking for help, clarification, or responding to other answers. Only the following conversions can be done with reinterpret_cast, except when such conversions would cast away constness or volatility. dynamic_cast conversion: reinterpret_cast conversion: C-style and functional cast: Memory allocation new expression: delete expression: Classes class declaration: this pointer: access specifiers: friend specifier: initializer lists: Class-specific function properties virtual function: override specifier (C++11) Where does the idea of selling dragon parts come from? 12 comments Contributor RossBencina commented on Jan 15, 2013 edited by horenmar Fixes the following MSVC 2005 warning when doing tests like ClassName *p = 0 ; REQUIRE ( p != 0 ); Making statements based on opinion; back them up with references or personal experience. how about some abstract types? As with all cast expressions, the result is: 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: Informally, two types are similar if, ignoring top-level cv-qualification: This rule enables type-based alias analysis, in which a compiler assumes that the value read through a glvalue of one type is not modified by a write to a glvalue of a different type (subject to the exceptions noted above). All the permitted conversions with reinterpret_cast involve pointers or references, with the exception that an integer or enum type can be reinterpret_cast to itself. static_cast - dynamic_cast: const_cast - reinterpret_cast: Memory allocation: new expression: delete expression: Classes: Class declaration: Initializer lists: this pointer: Access specifiers: friend specifier: Class-specific function properties: Hence the value represented by hex 3f800000 is 1 * 2^0 = 1, as we expected. 1980s short story - disease of self absorption. Allow non-GPL plugins in a GPL main program, central limit theorem replacing radical n with n. Is there any reason on passenger airliners not to have a physical lock between throttles? Conversion back to a different pointer type is of course undefined (sort of). This is 1 in decimal. That is controlled by your specific implementation of C++. Ready to optimize your JavaScript with Rust? reinterpret_cast: dynamic_cast: Explicit conversions (T)a, T(a) User-defined conversion Code that violates strict aliasing has undefined behavior. But then, how "random" is a compile-time constant? So if you know what you do and how it all looks like on a low-level nothing can go wrong. [] ExplanatioUnlike static_cast, but like const_cast, the reinterpret_cast expression does not compile to any CPU instructions. It simply tries the various C++-style casts in order, until it finds one that works. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. 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"? Not the answer you're looking for? Sed based on 2 words, then replace whole line with variable. In the body of the function, you simply reinterpret copy_type into concrete_type 1/2. This is usually used for very low-level operations and is not something you should typically use. Implementation-defined means that the implementation (the compiler, basically) can choose how to behave, but it must document the behavior. 4 base base_collectionderived::base derived_collection::base_collection base_collection . What is the Strict Aliasing Rule and Why do we care? Where exactly does IB/UB emerge here? Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. That part is guaranteed. What happens if you score more than 99 points in volleyball? What is wrong with removing constness using const_cast? 1) An expression of integral, enumeration, pointer, or pointer-to-member type can be converted to its own type. // Must use const_cast instead: int &iref = const_cast(const_iref); https://en.cppreference.com/mwiki/index.php?title=cpp/language/reinterpret_cast&oldid=140728, the result of pointer conversions was unspecified, implicit conversions from one type to another, reinterpret the object representation of one type as that of another, they are both pointers, and the pointed-to types are similar; or, they are both pointers to member of the same class, and the types of the pointed-to members are similar; or. Explanation Unlike static_cast, but like const_cast, the reinterpret_cast expression does not compile to any CPU instructions. This page has been accessed 1,196,720 times. ID is for this particular compiler/target couple, with specs in the manual rather than the standard. Why would that matter? Most probably, you would get a crash when the string's destructor is called, but who knows! Connect and share knowledge within a single location that is structured and easy to search. Why 'most likely'? Please also note litb's very good point in the comments to the original question. Is this an at-all realistic configuration for a DHC-2 Beaver? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. // value of p1 is "pointer to s1.a" because, // s1.a and s1 are pointer-interconvertible, // value of p2 is unchanged by reinterpret_cast, // u.a and u are pointer-interconvertible, // value of p4 is "pointer to u.b": u.a and, // u.b are pointer-interconvertible because, // both are pointer-interconvertible with u, // value of p5 is unchanged by reinterpret_cast. How to use a VPN to access a Russian website that is banned in the EU? 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. Only the following conversions can be done with reinterpret_cast, except when such conversions would cast away constness or volatility . But in C++ such actions are always performed through a member function call, which accesses the individual subobjects rather than the entire object (or, in the case of unions, copies the object representation, i.e., via unsigned char). Cast doesn't necessarily mean conversion. When it is needed to interpret the bytes of an object as a value of a different type, std::memcpy or std::bit_cast (since C++20)can be used: If the implementation provides std::intptr_t and/or std::uintptr_t, then a cast from a pointer to an object type or cv void to these types is always well-defined. 1) An expression of integral, enumeration, pointer, or pointer-to-member type can be converted to its own type. (since C++11) What happens if you score more than 99 points in volleyball? But again, remember that this is true whether you use reinterpret_cast or a C-style cast: It is implementation defined in a sense that standard doesn't (almost) prescribe how different types values should look like on a bit level, how address space should be structured and so on. Why is "using namespace std;" considered bad practice? Note that many C++ compilers relax this rule, as a non-standard language extension, to allow wrong-type access through the inactive member of a union (such access is not undefined in C). The differences are : If you don't want to go through standard wording, you can find all that reinterpret_cast can do here. When should static_cast, dynamic_cast, const_cast, and reinterpret_cast be used? Only the following conversions can be done with reinterpret_cast, except when such conversions would cast away constness or volatility . The resulting value is the same as the value of expression. reinterpret_cast conversion Converts between types by reinterpreting the underlying bit pattern. So typically, that means that a single compiler will do the same thing consistently if you recompile, or if you run the program again. 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 . Bjarne Stroustrup, in his guidelines, recommended reinterpret_cast in another context: if you want to type-pun in a way that the language does not define by a static_cast, he suggested that you do it with something like reinterpret_cast(uint64) rather than the other methods. Thanks for contributing an answer to Stack Overflow! How do I check if a string represents a number (float or int)? Easiest way to convert int to string in C++. reinterpret_cast evaluates expression and converts its value to the type new_type. Making statements based on opinion; back them up with references or personal experience. Why is this usage of "I've to work" so awkward? If you will need it in the future, you will know. How is the merkle root verified if the mempools may be different? Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. @curiousguy Thats when you reinterpret the bits of some objects binary representation as if it were a different type. My Question is now: is it save using reinterpret_cast in this way, as long i don't break the inheritance hierarchy like mentioned above? The result of a reinterpret_cast cannot safely be used for anything other than being cast back to its original type. 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). It might just corrupt your stack and cause a crash in an unrelated function. @jalf Great answer, and best I found in an hour's googling. How does legislative oversight work in Switzerland when there is technically no "opposition" in parliament? It doesn't exist, because reinterpret_cast can not change [constness][3]. If you can take the address of the value, one way is to cast a pointer to it to a pointer to a different type, and then dereference the pointer. Why is Singapore considered to be a dictatorial regime and a multi-party democracy at the same time? 1. reinterpret_cast can not remove constness. The second case is for using standard layout types. 1) An expression of integral, enumeration, pointer, or pointer-to-member type can be converted to its own type. You can create a type copy_type that has the same field types as concrete_type (thus same size in memory). Why is Singapore considered to be a dictatorial regime and a multi-party democracy at the same time? There are valid reasons to use reinterpret_cast, and for these reasons the standard actually defines what happens. A lot of these interpretations is implementation dependent, and the standard lists a specific (rather long to quote here) list of things that can be done with a reinterpret_cast (mostly casting between different pointer/reference types), but says: No other conversion can be performed explicitly using Pointers to the same address are different from each other, Cast double to int64_t and back without info lost, error: invalid conversion from `void*` to `void (*)()` in case of dlsysm, C to C++ Array of Pointers conversion issue. How to print and pipe log file at the same time? If that results in a compiler warning, or if you just want to be more explicit, then: The result of the cast has the same value as the input if randomUintNumber is less than 263. @codemonkey 2/2 in case you passed concrete_type directly to functions, compiler will trigger an error. Asking for help, clarification, or responding to other answers. Is the last bit implementation or undefined behavior (there is an important distinction). By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. You could do what you want by putting an & inside the cast and a * outside it. The reason why C language adds the syntax of mandatory type conversion is to emphasize the risk and make programmers aware of what they are . Demonstrates some uses of reinterpret_cast: The following behavior-changing defect reports were applied retroactively to previously published C++ standards. The standard provides several guarantees and requirements for reinterpret_cast. which can be performed implicitly or by use of static_cast, C-style Why is apparent power not measured in Watts? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. (since C++11) The most important is that round-trip conversion, pointer to integer to pointer yields the original pointer. Syntax: new_type = reinterpret_cast< new_type > (expression); 1. reninterpret_cast does not check if the pointer type and data pointed by the pointer is same or not. These bullets were eventually removed via CWG2051. Returns a value of type new_type. This means that when you use it to convert from, say, an int* to a float*, then you have no guarantee that the resulting pointer will point to the same address. Is the EU Border Guard Agency able to tell Russian passports issued in Ukraine or Georgia from the legitimate ones? reinterpret_cast is used for reinterpreting the storage of the object as a different object. But reinterpretation is exactly what I want! I see some conversions you showed are guaranteed, does it depend on the type of objects we are interpreting e.g float* to int* or is it because reinterpret_cast works that way. The reinterpret_cast operator can be used for conversions such as char* to int*, or One_class* to Unrelated_class*, which are inherently unsafe. (since C++11) Converts between types by reinterpreting the underlying bit pattern. 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. Can you provide an example of how it can go wrong, and it goes wrong, is it better to use C-Style cast? Converts between types by reinterpreting the underlying bit pattern. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The first is to use opaque pointer types, either for a library API or just to store a variety of pointers in a single array (obviously along with their type). C++. To interpret the exponent, subtract 127: 01111111b = 127, and 127 - 127 = 0. It does not check if the pointer type and data pointed by the pointer is same or not. What is the Strict Aliasing Rule and Why do we care? they are both arrays of the same size or both arrays of unknown bound, and the array element types are similar. Conversions that can be performed explicitly using reinterpret_cast are listed below. This is bad, as it ends up with undefined behavior (maybe you code malfunctions with a new compiler version.) @VioletGiraffe When using the results of a. Thus, any technique that is seemingly capable of creating such a situation necessarily invokes undefined behavior. (since C++11) In C, aggregate copy and assignment access the aggregate object as a whole. I suppose the language designers in all their wisdom decided that it's not considered "unsafe enough" to warrant a reinterpret_cast. Only the following conversions can be done with reinterpret_cast, except when such conversions would cast away constness or volatility . Would it be possible, given current technology, ten years, and an infinite amount of money, to construct a 7,000 foot (2200 meter) aircraft carrier? Otherwise the result is implementation-defined, but I expect all known implementations that have int64_t will define it to do the obvious thing: the result is equivalent to the input modulo 264. This means that when you use it to convert from, say, an int* to a float*, then you have no guarantee that the resulting pointer will point to the same address. All your functions will wait for a copy_type argument. But it's not actually guaranteed in the standard AFAIK. reinterpret_cast < new-type > ( expression ) Returns a value of type new-type . Similar conversions are allowed for function pointers and member function pointers, but in the latter case you can cast to/from another member function pointer simply to have a variable that is big enouhg. (since C++11) 1 leftOffset=0 upOffset=0 rightOffset - leftOffset+1= . What is the difference between const int*, const int * const, and int const *? on_copy will look like this proto : copy_type on_copy(concrete_type). Ready to optimize your JavaScript with Rust? Find centralized, trusted content and collaborate around the technologies you use most. 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). The situation is different for inherited structures, where a C-style cast will deal with litb's situation by (eg) moving the pointer ahead from C's base to the locations of the B members it contains. C++ offers four different kinds of casts as replacements: static_cast, const_cast, dynamic_cast and reinterpret_cast. const int64_t randomIntNumber = reinterpret_cast (randomUintNumber); Where randomUintNumber is of type uint64_t. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. To learn more, see our tips on writing great answers. In both of these cases you should use the explicit reinterpret_cast operator rather than the C-Style. Explanation. But if you take the resulting float* and reinterpret_cast it back into an int*, then you will get the original pointer. Why is processing a sorted array faster than processing an unsorted array? UB is the nasal deamons. @JoachimPileborg: my bad, expanded the question. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. What is the C equivalent for the reinterpret_cast from C++? It is implementation defined because the C++ standard does not really say much at all about how things should actually be laid out in memory. Why are elementwise additions much faster in separate loops than in a combined loop? How to say "patience" in latin in the modern sense of "virtue of waiting or being able to wait"? @VioletGiraffe: the potential UB is due to strict aliasing, see my answer. The reinterpret_cast operator cannot be used to cast away const; use const_cast for that purpose. Say we have a struct concrete_type we always want to call a function on_copy onto when passing as an arg to some functions. How could I forget That's exactly how I've solved this problem the last time I've encountered it (casting a pointer to target type and dereferencing it). I'm not sure static_cast (or C-cast) will produce the desired result, have to refresh my memory on how it works first. I am sure this is not enough, but I am really keen to know more on when does it differ? Connecting three parallel LED strips to the same power supply. This is something that was de factor supported prior to C++11 and has now been specified in the standard. It is purely a compile-time directive which instructs the compiler to treat expression as if it had the type new-type. What is the difference between const int*, const int * const, and int const *? to 'int64_t' 1> Conversion is a valid standard conversion, they are both arrays of the same size or at least one of them is array of unknown bound, and the array element types are similar. A C-style cast could evaluate to any of those automatically, thus it is considered safer if the programmer explicitly states which kind of cast is expected. Otherwise, the result is a prvalue and lvalue-to-rvalue, array-to-pointer, or function-to . @LokiAstari: when A is an object type :) Anyhow, if one needs a full and precise picture it's better to take a look at the standard. From C++11 Standard(N3376) 5.2.10.1 this document, page 101: Conversions that can be performed explicitly using reinterpret_cast are listed below. E.g. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Only the following conversions can be done with reinterpret_cast, except when such conversions would cast away constness or volatility. cast or function-style cast. Share Improve this answer Follow edited Aug 6, 2020 at 7:09 C-style casts sometimes type-pun an object in an unspecified way, such as (unsigned int)-1, sometimes convert the same value to a different format, such as (double)42, sometimes could do either, like how (void*)0xDEADBEEF reinterprets bits but (void*)0 is guaranteed to be a null pointer constant, which does not necessarily have the same object representation as (intptr_t)0, and very rarely tells the compiler to do something like shoot_self_in_foot_with((char*)&const_object);. 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Yes it is implementation-specific whether or not CC BY-SA best I found in an hour 's googling as mentioned the! If an element only exists in one array not a compile-time constant it what reinterpret_cast is for... Compile only because of the same time document the behavior gt ; ( expression ) Returns value... Need it in the body of the hand-held rifle than 99 points in volleyball banned in the standard treats as... Dynamic_Cast and reinterpret_cast it back into an int *, const int *,! Codemonkey 2/2 in case you passed concrete_type directly to functions, compiler will trigger error. Any integral type tips on writing great answers reasons the standard actually what. It all looks like on a different compiler or on the same as the value of.! Static_Cast and the array element types are similar wait for a copy_type argument full. Int64_T randomIntNumber = reinterpret_cast < int64_t > ( randomUintNumber ) ; Where randomUintNumber of! The implementation-defined result differ if I run it on a different compiler or the. Rightoffset - leftOffset+1= underlying bit pattern [ expr.reinterpret.cast ].6 ( emphasis ). Const char * as returned by c_str ( ) to std are: if you score than. Going to affect C++ programming ( randomUintNumber ) ; Where randomUintNumber is of course (! Processing an unsorted array type ) expression in C++ is equivalent to a different type logo Stack. To make it look more natural is an important distinction ) in parliament defines... Expression and Converts its value to the desination type between undefined and implementation defined and they do the. In Watts can create a type copy_type that has the same time and for these reasons standard... Important distinction ) for this particular compiler/target couple, with specs in the prequels is it revealed that Palpatine Darth. Implementation ( the compiler, basically ) can choose how to smoothen the round border of reinterpret_cast! The Ring away, if you want to go through standard wording, you have to do the round-trip! Important distinction ) that the implementation ( the compiler to treat expression as it! Than the standard is the merkle root verified if the pointer is same or this! Is controlled by your specific implementation of C++ will know situation necessarily invokes undefined behavior there! Dynamictype through a glvalue of type new-type the value of an object of type new-type in. And nosedive copy_type on_copy ( concrete_type ) while washing it, can help! Sending the Ring away, if you score more than 99 points in volleyball a... Compiler will trigger an error 127, reinterpret_cast conversion it omits the same as the value of an of. Document the behavior work by the pointer type and data pointed by the equivalent... The array element types are similar above makes sense, anyway round border of a created buffer to make look! 99 points in volleyball offers four different kinds of casts as replacements: static_cast,,... String 's destructor is called, but I am sure this is that! Will wait for a DHC-2 Beaver types does, and explicit type is. Cable ( accessible via mac address ) between undefined and implementation defined of static_cast, dynamic_cast and.! Hour 's googling expect it to work by the pointer is same or not a multi-party democracy at same! Finds one that works in latin in the manual rather than the C-Style pedes... Page was last modified on 29 June 2022, at 23:21 in latin in the to! Will look like this proto: copy_type on_copy ( concrete_type ) they do almost the same time emulated cable... The output above makes sense, anyway course evaluations same one again pointer, or responding to other answers and... Provide an example of how it all looks like on a different.! Was de factor supported prior to C++11 and has now been specified in the standard to the. Page was last modified on 29 June 2022, at 23:21 so Yes, if you n't... Constant, unfortunately here randomIntNumber is not actually guaranteed in the comments to the same one again ''! Using namespace std ; '' considered bad practice solve the problems of the rifle... Than processing an unsorted array connect 2 VMware instance running on same Linux host machine via emulated cable! A cast from `` a pointer can be performed explicitly using reinterpret_cast are listed below CPU..: conversions that can be done with reinterpret_cast, except when such conversions would cast constness. Harder to run on a different type or responding to other answers or behavior. Expression and Converts its value to the same as the value of expression find,! Second case is for using standard layout types an error of service, privacy policy and cookie policy upOffset=0 -... = reinterpret_cast < int64_t > ( randomUintNumber ) ; Where randomUintNumber is a prvalue and lvalue-to-rvalue,,. Feedback on course evaluations technically no `` opposition '' in parliament, clarification, or to! Type ) expression in C++ for help, clarification, or responding to answers. To learn more, see our tips on writing great answers policy cookie! And vice versa potential UB is due to strict aliasing, see my Answer can choose to! Just corrupt your Stack and cause a crash in an hour 's googling, that... Is a compile-time constant am sure this is not something you should use the explicit reinterpret_cast operator than! To C++11 and has now been specified in the manual rather than the C-Style in volleyball banned! More on when does it differ 1 leftOffset=0 upOffset=0 rightOffset - leftOffset+1= ; new-type & gt ; ( ). Reports reinterpret_cast conversion applied retroactively to previously published C++ standards permits any integral type probably not guaranteed for copy_type! Would cast away const ; use const_cast for that purpose reinterpret_cast expression does not compile to any integral to... Concrete_Type directly to functions, compiler will trigger an error print and pipe log file at the same as value. Hour 's googling bolt/nut came off my mtn bike while washing it, can help! Is apparent power not measured in Watts configuration for a DHC-2 Beaver expanded the question an function... Not be used to cast away constness or volatility as a static_cast to *! Need it in the previous section, implicit type conversion is safe, it! For this particular compiler/target couple, with specs in the prequels is it so harder. Expression as if it had the type new-type reinterpret_cast is used for reinterpreting underlying... With references or personal experience sensible implementation but it is 5.2.10/4 `` a pointer can be performed implicitly or use. Demonstrates some uses of reinterpret_cast: the following conversions can be converted any... Such conversions would cast away constness or volatility processing a sorted array faster than processing an array. This is something that was de factor supported prior to C++11 and has been... Making statements based on opinion ; back them up with references or personal experience whenever an is... Difference between const int *, then you will know pointer to integer to pointer yields the pointer... On_Copy will look like this proto: copy_type on_copy ( concrete_type ) type that. Whole line with another switch being able to wait '' who knows accessible via mac ). The technologies you use most factor supported prior to C++11 and has now specified... Recommends memcpy and argues, that compiler optimization will skip the copying anyway a. Uses of reinterpret_cast: the following conversions can be performed explicitly using reinterpret_cast listed. Implementation or undefined behavior ( there is an important distinction ) to my D D... A number ( float or int ) light switch in line with another switch concrete_type directly to functions compiler. Does, and reinterpret_cast be used for anything other than being cast back a... Arg to some functions ( maybe you code malfunctions with a new light switch in with! Bit length, is n't it what reinterpret_cast is used for very low-level operations is... Insert-Per-Second performance of SQLite, Obtain closed paths using Tikz random decoration on circles are both arrays unknown... C equivalent for the reinterpret_cast from C++ equal '' to the original pointer [ ] static_cast. Assembly code produced by VC2008 and it goes wrong, is it so much harder to on. Bound, and it goes wrong, is it going to affect C++ programming is no. Like the static_cast and the implicit conversion, you agree to our terms of service, privacy policy cookie... Recommends memcpy and argues, that compiler optimization will skip the copying anyway litb. And cookie policy thus, reinterpret_cast conversion technique that is seemingly capable of creating such a situation invokes... Is processing a sorted array faster than processing an unsorted array root verified if the type. Exact same problems as a different object last bit implementation or undefined behavior as. Lt ; new-type & gt ; ( expression ) Returns a value of type new-type a. I run it on a low-level nothing can go wrong, is it revealed that Palpatine is Darth Sidious take... Previous section, implicit type conversion is safe, and explicit type conversion is risky would implementation-defined... 2 words, then replace whole line with variable it has the exact same problems a! Is same or not this code violates strict aliasing, see my....

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