Look here: > I agree that this integral promotion rule is pretty weird. Your code has to be generic and works properly on big endian (e.g. You only need to use it when you're casting to a derived class. First you have some data in a specific type like int here: Then you want to access the same variable as an other type like float: It is efficient because it does not copy the value. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The Input struct can be casted to the Buffer before being sent over the wire. ; AIPP; Batch; ; ; Shape Range; Profiling; . A reinterpret_cast operator handles conversions between unrelated types. This cast operator can also convert variable into totally incompatible type too. My way of describing static_cast is that it supports two functions: 1. So when you convert int* to float* with this keyword, the new value (after pointer dereferecing) has nothing to do with the old value in mathematical meaning (ignoring the fact that it is undefined behavior to read this value). The rubber protection cover does not pass through the hole in the rim. Reinterpret casts are only available in C++ and are the least safe form of cast, allowing the reinterpretation of the underlying bits of a value into another type. You should use it in cases like converting float to int, char to int, etc. 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. static_cast<type> (variable) . 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. In most cases the 2 casts do the same thing but static_cast is far more restrictive than reinterpret_cast. So the two variables can be seen as different projections over the same memory zone. reinterpret_cast The next kind of cast is reinterpret_cast. This cast operator can convert an integer to a pointer and so on. reinterpret_cast < > ( ) static_cast const_cast reinterpret_cast CPU reinterpret_cast 1) (C++11 ) . Note that this solution doesn't guarantee to cast pointers on a functions. x86) systems. In your first example, you are using reinterpret_cast to cast from unsigned int to int. Re: reinterpret_cast in OpenCL1.1 OpenCL C is, as the name says, C and not C++, so there is no reinterpret_cast. reinterpret_cast static_cast static_cast reinterpret_cast static_cast , . (which is not the same as a valid pointer to another type). s. Last modified: 2021-12-03 16:33:54 UTC. The normal cast like (int)x is C style typecasting where static_cast(x) is used in C++. Read the FAQ! The only cast that raises more flags is a const_cast. Others have pointed out that the standard defines different rules for the two kinds of cast. Unlike C, the C++ compiler allows implicit conversions TO a void * type, but to convert FROM a void * type requires an explicit cast. You can use pointers to constant data as function parameters to prevent the function from modifying a parameter passed through a pointer. The reinterpret_cast operator converts a null pointer value to the null pointer value of the destination type. a Question In C like cast sometimes we can cast some type pointer to point some other type data. Let's imagine the example: you have to read binary 32bit number from file, and you know it is big endian. In short, static_cast<> will try to convert, for example, float-to-integer, while reinterpret_cast<> simply changing the compiler's intent to reconsider that object as another type. Which typically means that it's the same size as a pointer. So for your use case, it seems fairly clear that the standardization committee intended for you to use static_cast. Why is it so much harder to run on a treadmill when not holding the handlebars? Ascend Graph. The only required parameter is the class identifier, as the next example shows: C++. Though it says to use `reinterpret_cast` to convert from one pointer type to another? What is this fallacy: Perfection is impossible, therefore imperfection should be overlooked, I want to be able to quit Finder but can't edit Finder's Info.plist after disabling SIP, Penrose diagram of hypothetical astrophysical white hole. Thanks. On the other hand, when you call reinterpret_cast the CPU does not invoke any calculations. https://bugs.llvm.org/show_bug.cgi?id=38201 Bug ID: 38201 Summary: incorrect reinterpret_cast from integer to pointer error on invalid constexpr initialization . Though from what I have been reading it appears `static` is better as the cast can happen at compile time? return reinterpret_cast<QTimerPrivate *>(qGetPtrHelper (d_ptr)); clang diagnostic pop } inline const QTimerPrivate* d_func() const noexcept { clang diagnostic push return reinterpret_cast The example is wrong. If we go ahead and replace the macro with a constant expression, we should get the warning at the exact location where the C-cast is written, not where the macros are expanded. The static_cast correctly returns the address of the embedded A object, and the pointer created by static_cast correctly gives the value of the data field. The result of a reinterpret_cast cannot safely be used for anything other than being cast back to its original type. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. Why do we have reinterpret_cast in C++ when two chained static_cast can do its job? Note that a C-style (T)expression cast means to perform the first of the following that is possible: a const_cast , a static_cast , a static_cast followed by a const_cast , a reinterpret_cast , or a reinterpret_cast followed by a const_cast . It could not work as intended (or even crash) on other architectures -- for example it could be possible that floats and longs are stored in separate memory compartments (not that I know of any such architecture, it's just an argument). c-v qualified means const and volatileFor e.g:- // non cv_qualified int first; char *second; // cv-qualified const int third; volatile char * fourth; https://stackoverflow.com/questions/27527642/what-does-cv-qualified-mean/27527673#27527673. NOTE: In both cases you should save the casted value in a variable before cast! What is a smart pointer and when should I use one? Given a cast from a buffer to a struct: buffer is a pointer, thus its value is an address. Better way to check if an element only exists in one array. A pointer to a variable declared as const can be assigned only to a pointer that is also declared as const . For casting to and from void*, static_cast should be preferred. Though it says to use reinterpret_cast to convert from one pointer type to another? Huge difference. static\u castv[0] int reinterpret\u cast reinterpret_cast OK, true, but I don't care about a version from 13 years ago, and nor should most coders if (as is likely) they can avoid it. static_cast - dynamic_cast. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. If you use static-casting, it will always be 0000'0001, no matter what endianness is being used. Casting can also hide other subtle bugs. reinterpret_cast. A const_cast , dynamic_cast , or reinterpret_cast will never create a new class-type object, and thus will never call a constructor. This is the cast the C++ compiler uses internally for implicit casts also. One typical way to do type punning in C++ is to read the member of a union with a different type from the one with which it was written. Its basically only relevant&valid when reinterpreting raw bytes as objects (which has limitations) and vice versa. This is also the cast responsible for implicit type coercion and can also be called explicitly. Your example of converting a void* to a Class type should use static_cast as a conversion from void* to T* is a well defined conversion by the compiler as a void* is a valid pointer to a class type. As a rule of thumb, use reinterpret_cast if there is no implicit conversion and static_cast is rejected by the compiler - and you are really sure that it's the conversion you need. again, if like me you're happy to limit yourself only to platforms that play nice with the latest and greatest version of the language, your objection is a moot point. reinterpret_cast will permit a cast between any two pointers. One use of reinterpret_cast is to convert a pointer to an unsigned integer (when pointers and unsigned integers are the same size): int i; One case when reinterpret_cast is necessary is when interfacing with opaque data types. For example, in the spoof checker API, you deal with pointers of type, @yeputons that's the reason why reinterpret_cast'ing. The meaning of reinterpret_cast is not defined by the C++ standard. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. The typecasting using this is done at compile time. The " reinterpret_cast " operator can convert any type of variable to fundamentally different type. reinterpret_cast operator syntax reinterpret_cast < Type > ( expression ) With the right angle bracket feature, you may specify a template_id as Typr in the reinterpret_cast operator with the >> token in place of two consecutive > tokens. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. It is used to change the constant value of any object or we can say it is used to remove the constant nature of any object. Manually incrementing and decrementing a boost::shared_ptr? One practical use of reinterpret_cast is in a hash function, which maps a value to an index in such a way that two distinct values rarely end up with the same index. reinterpret_cast is not allowed in constexpr functions, First of all, this code is rejected by both latest clang (7.0.0) and gcc (8.2.0). When a pointer or reference to object of type T1is reinterpret_cast(or C-style cast) to a pointer or reference to object of a different type T2, the cast always succeeds, but the resulting pointer or reference may only be accessed if one of the following is true: T2 is the (possibly cv-qualified) dynamic type of the object ; Operator . Note that the type of the pointer has to match the type of the variable you're working with. The C++ standard library gained some new concurrency features with C++20: Wait and notify operations on std::atomic<T>; Semaphores; Latches; Barriers; In this article, I will cover the current implementation approach for atomic wait/notify, as these are basis operations required to implement the remaining coordination primitives introduced with C++20. (in practice it will typically contain the same address as a and c, but that's not specified in the standard, and it may not be true on machines with more complex memory systems.). Asking for help, clarification, or responding to other answers. reinterpret_cast , . This prevents possible data loss. You can decide between. I have seen usage of both static_cast and reinterpret_cast? This is exclusively to be used in inheritence when you cast from base class to derived class. @HeretoLearn, is it possible to add the relevant code pieces from the *.c and *.cpp file? If you continue to use this site we will assume that you are happy with it. After reinterpret-casting the byte under p pointer could be respectively 0000'0000 or 0000'0001. There are no run-time checks. This is another "free" cast that generates no CPU instructions. Get a free answer to a quick problem. answered 05/05/20, Senior Software Engineer Specializing in Systems Programming. Choose an expert and meet online. Your email address will not be published. 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. Type punning is the possibility of a programming language intentionally subvert the type system to treat a type as a different type. This is a serious pitfall if alignment does not match that *will* lead to crashes on even medium optimization levels 3 reflexpr-sarah- 3 yr. ago no, the second one has defined behavior, as long as the object is trivially copyable https://en.cppreference.com/w/cpp/string/byte/memcpy 1 2 more replies Gotebe 3 yr. ago A tag already exists with the provided branch name. Update: As I was told, the sizes of the two types should be equal. That is, in the following, a, b and c all point to the same address: reinterpret_cast only guarantees that if you cast a pointer to a different type, and then reinterpret_cast it back to the original type, you get the original value. Required fields are marked *. const_cast,dynamic_cast,reinterpret_cast,static_castconst_castdynamic_castreinterpret_caststatic_cast C++CNewTypeExpressionC++. Casting implies a pointer copy, which is very cheap. Too much to remember. You should use bit_cast or memcpy. Save my name, email, and website in this browser for the next time I comment. Now, we have got a complete detailed explanation and answer for everyone, who is interested! We can only use this in particular situations. A use case for reinterpret_cast is transporting data through a buffer. The Strict aliasing rule allows us to avoid redundant machine code in cases in which it should be safe to assume that two pointers don't point to the same memory block (see also the restrict keyword). 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. 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. Similarly, something like -Wunsafe-functional-cast for any functional-style cast T(x) . If you are unable to find uses for these casts, then count your blessings. Although the reinterpret_cast itself might be unspecified behaviour, attempting to access the parameters once you've done the cast is undefined behaviour. hr = pFileOpen.CoCreateInstance (__uuidof (FileOpenDialog)); The CComPtr::CoCreateInstance method is provided purely as a convenience; you can still call the COM CoCreateInstance function, if you prefer. For example, if you want to dump the double with value 5.14 as the 8 bytes it's made of in memory, and not as the four bytes of its decimal text representation (like I did in the first example): #include <fstream> int main(){ double d = 5.14; std::ofstream("terca.bin", std::ios::binary).write( reinterpret_cast<char*>(&d), sizeof d); } This . ICU is an example of a library that does this in several places. It compiles fine on the newest gcc (8.3.0) but the standard says it is illegal. Be aware that reading or modifying values after reinterprt_cast'ing are very often Undefined Behavior. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. This may be a late question, but why doesn't the vendor API use. Please note: ALL of this happens at compile time. reinterpret_cast<> () is used for casting between unrelated types. The result is then bit-shifted and XORed with itself to produce a unique index (unique to a high degree of probability). Misuse of the reinterpret_cast operator can easily be unsafe. Pointer Type Pointer conversion is a bit complicated, and we'll use the following classes for the rest of this article: class CBaseX { public: int x; It is used to change the constant value of any object or we can say it is used to remove the constant nature of any object. const_cast can be used in programs that have any object with some constant value which need to be changed occasionally at some point. All I could find was. reinterpret_cast indicates non-portable code any time it is used. However, the OpenCL C standard defines a class of functions that has very similar functionality (and is, in fact, significantly more powerful): as_ type (), that includes both a vector and scalar version for each of the built-in types. A link to the app was sent to your phone. In fact you can always avoid reinterpret_cast in these pointer situations by doing void* beginPos = beginMemory + bytePos; uint32_t lockTime = *(static_cast<uint32_t*>(beginPos)); Of course this will only work if the memory is really a block of type uint32_t*. The reinterpret_cast operator cannot be used to cast away const; use const_cast for that purpose. In cases of multiple inheritance reinterpret_cast will never perform delta arithmetic. Apr 11 '06 # 2 yuvalif you can make your IO more portable by converting to network endian A tag already exists with the provided branch name. This does not actually answer the question of "when to use reinterpret_cast". const_cast is one of the type casting operators. Holding C++ data in C can be risky. Our team has collected thousands of questions that people keep asking in forums, blogs and in Google questions. The reinterpret_cast allows the pointer to be treated as an integral type. C* is not on the path so static_cast will produce compile-time error. Also allows any integral type to be converted into any pointer type and vice versa. How to say "patience" in latin in the modern sense of "virtue of waiting or being able to wait"? To learn more, see our tips on writing great answers. Syntax : Is this an at-all realistic configuration for a DHC-2 Beaver? reinterpret_cast reinterpret_cast . reinterpret_cast allows anything, that's usually a dangerous thing and normally reinterpret_cast is rarely used, tipically to convert pointers to/from integers or to allow some kind of low level memory manipulation. There are more explicit methods which allow us to describe the intention of our cast. I thought that reinterpret_cast<> guaranteed the same bit pattern. Everything here but the last example is undefined behavior; its interesting only as a (not reliable) means of illustrating implementation details of the language. A reinterpret_cast is unnecessary here and static_cast should be preferred. This rule bans (T)expression only when used to perform an unsafe cast. In some cases, using reinterpret_cast does not scale well, though apparently could help to design decoupled components. static_cast only allows conversions like int to float or base class pointer to derived class pointer. If you know what the compilers you are going to use do with reinterpret_cast you can use it, but to say that it is portable would be lying. If B has more than one base class, and A is not the first base class, reinterpret cast will do the wrong thing and fail to perform necessary adjustment to the pointer. Executing tasks based on static polymorphism, A more decoupled approach on static polymorphism. Memory allocation. The reinterpret_cast operator can be used for conversions such as char* to int*, or One_class* to Unrelated_class*, which are inherently unsafe. Reinterpret cast will always return a pointer. A tag already exists with the provided branch name. What it does copy is the pointer to the value. The purpose of reinterpret_cast is to reinterpret the bits of one value as the bits of another value. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content, Getting around the reinterpret cast limitation with constexpr, casting via void* instead of using reinterpret_cast, C++ gives strange error during structure initialization with an array inside. The reinterpret_cast operator cannot cast away the const, volatile, or __unaligned attributes. reinterpret_cast is used when you want to convert one type to another fundamentally different type without changing the bits. When should static_cast, dynamic_cast, const_cast, and reinterpret_cast be used? Unfortunately I did not find the limitation in formal language. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The standard offers a few guarantees about reinterpret_cast. As such, any time you do use it you need to ask yourself if what you are doing is in fact correct. The reinterpret_cast operator converts a null pointer value to the null pointer value of the destination type. And using this C++ cast the intensions are conveyed much better. Ready to optimize your JavaScript with Rust? Here's a contrived example where a vendor provides an API for storing and retrieving arbitrary global data: To use this API, the programmer must cast their data to VendorGlobalUserData and back again. That address is loaded into the rax registry: input is also a pointer (Input*). dynamic_cast is used with polymorphic & inherited types which are C++ only idioms. Answers and comments should really reflect the latest available Standard unless otherwise specified IMHO. JOIN ME:youtube https://www.youtube.com/channel/UCs6sf4iRhhE875T1QjG3wPQ/joinpatreon https://www.patreon.com/cppnutsplay list for smart pointers: https:/. const_cast can be used in programs that have any object with some constant value which need to be changed occasionally at some point. The clang compiler refuses to compile it (which is correct). It's probably incorporated in one of the next WPs. One example of this was the Fast Inverse Square-Root trick: https://en.wikipedia.org/wiki/Fast_inverse_square_root#Overview_of_the_code. The general rule is that you should only use reinterpret_cast when you have to. If you don't know what reinterpret_cast stands for, don't use it. It's a misconception that reinterpret_cast<T*> (p) would interpret the bits of p as if they were representing a T*. Are the S&P 500 and Dow Jones Industrial Average securities? The general idea I get is this is unportable and should be avoided. What happens if you score more than 99 points in volleyball? Keywords. 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. It only stop you when you remember it's unspecified. Most questions answered within 4 hours. This type of cast reinterprets the value of a variable of one type as another variable of a different type. No packages or subscriptions, pay only for the time you need. @Xeo They don't use void * because then they lose (some) type-checking at compile time. reinterpret_cast This is the trickiest to use. 0x80000000 is -0 for example (the mantissa and exponent are null but the sign, the msb, is one. This is what static_cast stands for. (str,) > input.read (reinterpret_cast<char *> (&value), sizeof (value)); // Whereinput > "has" > int It is and it isn't. About all you can say is that you're more or less guaranted to pass the address. It allows you to change the type of a pointer or reference haphazardly and provides no checks. Other uses are, at best, nonportable. Our experts have done a research to get accurate and detailed answers for you. This occurs frequently in vendor APIs over which the programmer has no control. From what I have read the general rules are to use static cast when the types can be interpreted at compile time hence the word `static`. Next use reinterpret_cast to cast the starting address of your array to an unsigned char*, and set each byte of the array to 1 (hint: you'll need to use sizeof to calculate the number of bytes in a double). I think it can improve the exposition of the question. Can Reinterpret_cast return null? The worst ever invented. dynamic_cast This cast is used for handling polymorphism. So, feel free to use this information and benefit from expert answers to the questions you are interested in! The general idea I get is this is unportable and should be avoided. . If you had used static_cast<> above what use is the 'b' anyway? In C++, a pointer to an object can be converted to void * without any casts. This also works for doubles and long doubles. This is your one-stop encyclopedia that has numerous frequently asked questions answered. It is efficient because it does not copy the value. Even if the Input is const. It is used to convert one pointer of another pointer of any type, no matter either the class is related to each other or not. Then the buffer, when received, can be converted back to the Input struct. Anyway, I guess the Committee felt the need to explicitly add this after 2003. It is true that "it means that the same memory is used as a different type" but it is restricted to specific pair of types. dynamic_cast (expr) The dynamic_cast performs a runtime cast that verifies the validity of the cast. I am little confused with the applicability of `reinterpret_cast` vs `static_cast`. What cast should be used to convert between the void * and the Class type? What cast should be used to convert between the `void *` and the Class type? reninterpret_cast does not check if the pointer type and data pointed by the pointer is same or not. It treats the binary representation of the float as an integer, shifts it right and subtracts it from a constant, thereby halving and negating the exponent. std::string my_std_string (my_txt, my_txt + my_txt_len); . Now use your array-printing function to print the results. You'd need a static_cast to get the original pointer back. It is dynamic_cast that is a static_cast with a run . en.cppreference.com/w/cpp/language/reinterpret_cast, social.msdn.microsoft.com/Forums/vstudio/en-US/, en.cppreference.com/w/cpp/language/constant_expression, github.com/cplusplus/draft/blob/master/papers/N3797.pdf, Using reinterpret_cast to check inheritance at compile time. , . Using reinterpret_cast to check inheritance at compile time. Connect and share knowledge within a single location that is structured and easy to search. The purpose of reinterpret_cast is to reinterpret the bits of one value as the bits of another value. The reinterpret_cast operator can be used for conversions such as char* to int*, or One_class* to Unrelated_class*, which are inherently unsafe. This type of cast reinterprets the value of a variable of one type as another variable of a different type. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. It is well-known on compile time so you can write constexpr function: You can write a function to achieve this: Explanation: the binary representation of x in memory could be 0000'0000'0000'0001 (big) or 0000'0001'0000'0000 (little endian). It may just not be a valid pointer in the sense that it actually points to an object of type B. . This will work, but this style of cast is not recommended in C++. This is exclusively to be used in inheritence when you cast from base class to derived class. Other uses are, at best, nonportable. Normal syntax to do reinterpret_cast is as follows: reinterpret_cast <target-type> (expr) reinterpret_cast is usually used for casting unrelated types. static_cast only allows conversions like int to float or base class pointer to derived class pointer. But reinterpret_cast won't. . We don't actually use that code, I was just trying to demonstrate what the actual value should be. More info about Internet Explorer and Microsoft Edge. Obviously, since both constructs are about as unsafe as it gets, dereferencing the result pointer ap could cause undefined behavior. If you cast something to another pointer type you are asking for problems and the fact that you can not depend on it makes you more careful. BRIEF: it means that the same memory is used as a different type. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. That is, reinterpret_cast from A to B to A is perfectly safe and well-defined. reinterpret_cast allows anything, that's usually a dangerous thing and normally reinterpret_cast is rarely used, tipically to convert poi. A practical use case of "opaque" data types is when you want to expose an API to C but write the implementation in C++. convert one pointer type to another. The standard says that this is undefined behavior: @sandthorn: This is UB according to the standard, but if it works for your architecture, don't worry about it. . The reinterpret_cast is UB. Welcome to FAQ Blog! [] 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 . But the cast itself is safe enough, as long as you only used it in the way the standard allows. In that case it will read the value of p using p 's type, and that value is then converted to a T*. Thanks for contributing an answer to Stack Overflow! 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. When you use this cast you are saying to your compiler, 'I know better than you do, I want you to reinterpret the bit pattern of this object as a different type'. It measure bytes of any object's size and is returned by sizeof operator. It is used for reinterpreting bit patterns and is extremely low level. Example: It is true that reinterpret_cast is not portable because of one reason - byte order (endianness). reinterpret_cast in C# You can achieve this but this is a relatively bad idea. (because IIRC, it was the same in C++11). This approach solves the requirements, but there is (at least) one design particularity that makes it hard to scale. Bug 95307 - Compiler accepts reinterpret_cast in constexpr. We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. Shorter syntax for casting from a List to a List? Yep, that's about the only meaningful use of reinterpret_cast I can think of. After converting back to a float, it's subjected to a Newton-Raphson iteration to make this approximation more exact: This was originally written in C, so uses C casts, but the analogous C++ cast is the reinterpret_cast. While this looks straightforward, playing with memory by converting from one type to another can be error-prone. See const_cast Operator for information on removing these attributes. ;), lol, I suspect that reinterpret_crash might indeed crash your program. Its recently that I needed to properly understand reinterpret_cast, which is a method of converting between data types. For the most part reinterpret_cast is only there to satisfy the compiler when you are doing an inherently unsafe conversion and an analog in C# would depends on what the actual types are as it is ultimately up to the CLR to decide if the type conversion can and will occur. reinterpret_cast allows anything, that's usually a dangerous thing and normally reinterpret_cast is rarely used, tipically to convert poi. This is a bad use of reinterpret_cast. We use cookies to ensure that we give you the best experience on our website. Does the collective noun "parliament of owls" originate in "parliament of fowls"? In the first version I made example function is_little_endian to be constexpr. size_t is an unsigned integer data type which can assign only 0 and greater than 0 integer values. It is similar in use to a plain C-style cast and generally static_cast should be preferred if possible because it will prevent you from accidentally trying to convert one type to an incompatible type like converting a struct type to a pointer type. static_cast only allows conversions like int to float or base class pointer to derived class pointer. Allows any pointer to be converted into any other pointer type. C++ _,c++,language-lawyer,reinterpret-cast,strict-aliasing,C++,Language Lawyer,Reinterpret Cast,Strict Aliasing What it does copy is the pointer to the value. unsigned int u = reinterpret_cast(&i); You could use reinterprete_cast to check inheritance at compile time. Making statements based on opinion; back them up with references or personal experience. Type alias declaration (C++11) Casts. In your example. Therefore, if your static_cast is between unrelated types then it will fail at compile type but the same cast will succeed using a reinterpret_cast. Not if you use it properly. Unless the desired conversion is inherently low-level, you should use one of the other cast operators. If a new property is added to the Message struct anywhere before or between the others, it will break one, multiple, or all the consumers. Its basically only relevant&valid when reinterpreting raw bytes as objects (which has limitations) and vice versa. Not quite crash your program. Similarly, -Whidden-const-cast. Connecting three parallel LED strips to the same power supply, Name of a play about the morality of prostitution (kind of), convert integer types to pointer types and vice versa. In C++0x, reinterpret_cast<int*> (p) will be equivalent to static_cast<int*> (p). This static_cast<>() can be spotted anywhere inside a C++ code. If you will need it in the future, you will know. If you will need it in the future, you will know. A value of type pointer to object converted to pointer to cv void and back to the original pointer type will have its original value. Just not as many as people often expect. reinterpret_cast: Casts anything which has the same size, for example, int to FancyClass* on x86. Your email address will not be published. Where I am a little confused is one usage which I need, I am calling C++ from C and the C code needs to hold on to the C++ object so basically it holds a `void*`. I like the fact that 'b' is undefined. Most of the use cases for reinterpret_cast are for old-style C pseudo-unions: struct sockaddr { unsigned short sa_family; char sa_data []; }; struct sockaddr_in { unsigned short sin_family; unsigned short sin_port; I have seen usage of both `static_cast` and `reinterpret_cast`? reinterpret_cast is the dangerous one. Why can't I reinterpret_cast uint to int? This can cast related type classes. The address loaded into rax is copied into the input pointer, which now points at the same memory zone as the buffer does. The index is then truncated by a standard C-style cast to the return type of the function. The const keyword can also be used in pointer declarations. `reinterpret_cast`s are applicable in two scenarios, convert integer types to pointer types and vice versa or to convert one pointer type to another. rev2022.12.9.43105. In most cases the 2 casts do the same thing but static_cast is far more restrictive than reinterpret_cast. So you could convert binary representations of floats as int type like above to floats. Not the answer you're looking for? It's used primarily for things like turning a raw data bit stream into actual data or storing data in the low bits of an aligned pointer. This is the cast the C++ compiler uses internally for implicit casts also. const_cast - reinterpret_cast. const_cast (expr) The const_cast operator is used to explicitly override const and/or volatile in a cast. 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. 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