const_cast add constness

Is it allowed to cast away const on a const-defined object as long as it is not actually modified? IMHO, this is a dangerous practice because it leads to strange errors when you accidentally free the "literal" string. Similarly, int** are not int const**. const_cast operator syntax const_cast < Type > ( expression ) With the right angle bracket feature, you may specify a template_id as Type in the const_cast operator with the >> token in place of two consecutive > tokens. It all becomes clearer when we see the pointer version. 1) Two possibly multilevel pointers to the same type may be converted between each other, regardless of cv-qualifiers at each level. A brief primer on const. overloading, const parameter, const_cast, const_cast. Their cast is resolved at compile time. int* turns into a const int* implicitly. Back-patching const correctness results in a snowball effect: every const you add "over here" requires four more to be added "over there." Add const early and often. Member types Example Edit & run on cpp.sh Output: checking constness A: true B: true C: true D: true E: false See also remove_const Remove const qualification (class template) add_volatile Add volatile qualification (class template) const_cast on a static array to add constness Asked 2 years, 10 months ago Modified 2 years, 10 months ago Viewed 214 times 1 I've faced need to pass non-const static array to const argument. The. So it makes sense to have different cast keywords. You cast away constness of the object itself, which is (a) unneeded because. Q: Why use const_cast?Ans: The main goal of const_cast is to remove the constness of some pointer and variable so that we can change the value of the underly. Sometimes its done when you share malloc'ed strings and "literal" and/or const strings in the same pointer. Examples of frauds discovered because someone tried to mimic a random sequence. QGIS Atlas print composer - Several raster in the same layout. In the cases where the operation is safe, it is almost always not required. Why doesn't Stockfish announce when it solved a position as a book draw similar to how it announces a forced mate? 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. In the cases where it is required to add const, its use is dangerous in hard to reason about ways. const_cast operator syntax 1 const_cast < Type > ( expression ) With the right angle bracket feature, you may specify a template_id as Type in the const_cast operator with the >> token in place of two consecutive > tokens. Why does this pointer/integer comparison generate a segmentation fault? Using C++ vector::insert() to add to end of vector, Template Metaprogramming - Difference Between Using Enum Hack and Static Const, How to add two numbers without using ++ or + or another arithmetic operator, Using decltype to get an expression's type, without the const. A pointer to a const object can be converted to a pointer to non-const object using the const_cast keyword. There are cases where you need to call const_cast in order to add const that will not happen implicitly. In the cases where it is required to add const, its use is dangerous in hard to reason about ways. const\u cast. The const_cast doesn't make it safer, it just hides the error. This is used for the normal/ordinary type conversion. In particular, only const_cast may be used to cast away (remove) constness or volatility. The result of const_cast(expression) belongs to one of the The compiler will Pretty sure I already knew that rectangles are not squares. Making statements based on opinion; back them up with references or personal experience. Are const members? Asking for help, clarification, or responding to other answers. Their cast is resolved at compile time. it's potentially (albeit unlikely) harmful. may add or remove any number of const or volatile modifiers. There are cases where you need to call const_cast in order to add const that will not happen . const. This is a specific case of the rectangle-square problem. Would it be possible to stop malloc'ing strings into const char * pointers in cpp without de-constifying it too much? T1 and T2 are object types, you can also But how is it about the other way around? Similarly, int** are not int const**. C++ style cast from unsigned char * to const char *. Is initialising const class fields using static methods good or bad practice? Add a new light switch in line with another switch? allow the *c = 30, but the behavior of this statement You should NEVER cast away constness. const_cast in C++ | Type Casting operators Difficulty Level : Hard Last Updated : 23 Aug, 2018 Read Courses @Sale Discuss Practice Video C++ supports following 4 types of casting operators: 1. const_cast 2. static_cast 3. dynamic_cast 4. reinterpret_cast However the code beyond would work but is it good style (according to my use case)? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Windows Dev Center Home ; UWP apps; Get started; Design; Develop; Publish; Resources . been explicitly declared as const, you can modify Types cannot be defined within const_cast. Anybody prefer a different approach? const_cast is dangerous because it makes it impossible for the C++ type system to prevent you from trying to modify a const object. In the case of pointers, a int*const* is a int const*const*: the mutability of the "higher level" pointers causes the problem.). Otherwise, it is T unchanged. Very helpful! rev2022.12.11.43106. To the compiler, the const qualifier on a method refers to physical constness: calling this method does not change the bits in this object.What we want is logical constness, which is only partly overlapping: calling this method does not affect the object in ways callers will notice, nor does it give you a handle with the ability to do so. LKML Archive on lore.kernel.org help / color / mirror / Atom feed * [PATCH 1/4] container_of: add container_of_const() that preserves const-ness of the pointer @ 2022-12-01 19:30 Greg Kroah-Hartman 2022-12-01 19:30 ` [PATCH 2/4] device.h: move kobj_to_dev() to use container_of_const() Greg Kroah-Hartman ` (6 more replies) 0 siblings, 7 replies; 14+ messages in thread From: Greg Kroah-Hartman . But why do you care? Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com> However, if you cast away the constness of an object that has not Get monthly updates about new articles, cheatsheets, and tricks. The following demonstrates the use of the const_cast operator: The compiler would not allow the assignment *b = 20 because b points may add or remove any number of constor volatilemodifiers. Finding the original ODE using a solution. respect to their const and volatile qualifiers. Would like to stay longer than 90 days. int main() { const int i = 5; int* p = const . Two string literals have the same pointer value? an lvalue. C++ lambda this pointer invalidation after move operation, What do these C++ functions return? You can use const to prevent modifications to variables and const pointers and const references prevent changing the data pointed to (or referenced). Why using the const keyword before and after method or function name? Your question states that char sourcebuffer[] = {0x00}; copyfunction(sourcebuffer); is an error, but that's not true. It can strip volatile, or make you miss the fact that const was added somewhere else in your variables and your const_cast now silently strips them. 1) Two possibly multilevel pointers to the same type may be converted between each other, regardless of cv-qualifiers at each level. Squares are not Rectangles, because if you change the width of a Square its height also changes, and this does not happen when you modify a Rectangle. rvalue of type pointer to T1 to type pointer to Const Correctness By Alex Allain The const keyword allows you to specify whether or not a variable is modifiable. // this->i = v; // compile error: this is a pointer to const, // const_cast(mfp); // compiler error: const_cast does not, http://en.cppreference.com/mwiki/index.php?title=cpp/language/const_cast&oldid=45406. Issues Pull Requests Milestones Cloudbrain Task Pull Requests Milestones Cloudbrain Task 2) lvalue of any type T may be converted to a lvalue or rvalue reference to the same type T, more or less cv-qualified. I expect you would not care > for this change, but thought I'd check to see where you draw the line: I'd call this kind of a wash, I guess. to or from a type. How to create const reference to pointer on const? A non-const variable can be implicitly casted to const. This is also the cast responsible for implicit type coersion and can also be called explicitly. On an aside, why is int * const* == int const * const *? Is there sense in using const std::string& arguments in C++17? const_castcan be used to remove or add const to a variable. It can do something you don't want it to do. Implications of a const_cast in a copy constructor? 1) Two possibly multilevel pointers to the same type may be converted between each other, regardless of cv-qualifiers at each level. + * container_of_const - cast a member of a structure out to the containing + * structure and preserve the const-ness of the pointer + * @ptr: the pointer to the member . To explicitly add const-qualification to an object, const_cast can be used. API (C),API,const. Does a 120cc engine burn 120cc of fuel a minute? For details, see Class templates (C++ only). A const_cast operator is used to add or remove a const or volatile modifier to or from a type. I thought declaring the parameter of the copyfunction as const assures the user of not modifying (read-only) the pointer or the location of the source buffer itself. const_cast ,const, const. following value categories: Type and the type of expression may only differ with This can be useful if it is necessary to add/remove constness from a variable. If T is const-qualified, this is the same type as T but with its const-qualification removed. Converts between types with different cv-qualification. PugiXML C++ getting content of an element (or a tag), Running Visual Studio 6 C++ in Windows 8.1. away constness: The result of a const_cast expression is an rvalue It can strip volatile, or make you miss the fact that const was added somewhere else in your variables and your const_cast now silently strips them. the object is already non-const and (b) doesn't affect the const-ness of. it safely. We're > dereferencing dentry to get a pointer value, and _that_ pointer value is > then subject to the pointer arithmetic. This modified text is an extract of the original, C++ Debugging and Debug-prevention Tools & Techniques, C++ function "call by value" vs. "call by reference", Curiously Recurring Template Pattern (CRTP), Conversion by explicit constructor or explicit conversion function, Derived to base conversion for pointers to members, RAII: Resource Acquisition Is Initialization, SFINAE (Substitution Failure Is Not An Error), Side by Side Comparisons of classic C++ examples solved via C++ vs C++11 vs C++14 vs C++17, std::function: To wrap any element that is callable. Concentration bounds for martingales with adaptive Gaussian steps. This can be useful if it is necessary to add/remove constness from a variable.static_castThis is used for the normal/ordinary type conversion. The transformed type is aliased as member type remove_const::type. Get references to the last two elements in std::list. to an object of type const int. T* converts implicitly to const T*. Are reference members good practice? ( ( (union { const typename cv; typename v; }*)& (value))->v) which requires value to be an lvalue, but avoid compiler warning (gcc) comparing . const_cast to reference type can be used to convert a const-qualified lvalue into a non-const-qualified value. Something can be done or not a fit? So if I add constness using reinterpret_cast and if you reinterpret_cast the result back to the original type, it should result back to the original type and . It can remove volatile from the pointer type, which is not the intention here and would result in undefined behavior if sourcebuffer were declared as volatile sourcebuffer[]. Is it a non-standard std::pair implementation, a compiler bug, or a non-standard code? Squares are not Rectangles, because if you change the width of a Square its height also changes, and this does not happen when you modify a Rectangle. the above call to assign_ptr only adds const, but it will not happen implicitly. The const-ness or not of dentry is completely irrelevant, > we're not doing any pointer arithmetic on that to obtain some other > pointer that morally should have the same const-ness. make the following types of conversions: If a conversion from a (prvalue) static_cast. Thanks! Data representation and constness are orthogonal. Why was USB 1.0 incredibly slow even for its time? the above call to assign_ptr only adds const, but it will not happen implicitly. In the above example, the object referred to by b1 has Is using "this" for all member functions and attributes bad practice? We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. std:: as_const C++ Utilities library 1) Forms lvalue reference to const type of t. 2) const rvalue reference overload is deleted to disallow rvalue arguments. If you cast away the constness of an object that has You may cast away the constness Two way C++ to C# communication using named pipes. In the case of pointers, a int*const* is a int const*const*: the mutability of the "higher level" pointers causes the problem.). C++ - using const reference to prolong a member of a temporary, ok or UB? T2 using const_cast, where > The following seems somewhere in between, with ItemPointer > changing to const ItemPointerData *. After const_cast, the value does not change in the main function. Ready to optimize your JavaScript with Rust? Do non-Segwit nodes reject Segwit transactions with invalid signature? Should I exit and re-enter EU with my EU passport or is it ok? Even though const_cast may remove constness from any pointer or reference, using the resulting pointer or reference to write to an object that was declared const invokes undefined behavior. C++: Difference between setting a pointer to nullptr and initializing it as a new variable type. diff --git a/fs/dcache.c b/fs/dcache.c C++ standard: dereferencing NULL pointer to get a reference? It only accepts a non-const char* argument even though it never writes through the pointer: const_cast to reference type can be used to convert a const-qualified lvalue into a non-const-qualified value. That is causing 48 million of set->add() calls in collect_glyphs(), which is insane. I'd be more excited about it if the change allowed removal of an actual cast-away-of-constness somewhere. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. Sure, now I could simply declare the sourcebuffer as const but in my case I don't have access to that variable because it's from a different code location (external library). const_cast operator with the >> token in place of two HarfBuzz text shaping library (new rewritten version) behdad: summary refs log tree commit diff ClassA*& func1(). const_cast is applied to expressions, not objects, and itself is an expression as well: 5.2.11 [expr.const.cast]/p1: The result of the expression const_cast<T>(v) is of type T. If T is an lvalue reference to object type, the Zorn's lemma: old friend or historical relic? const_cast - Removing the constness of a simple integer . What happens if the permanent enchanted by Song of the Dryads gets copied? const_cast<Type>(expression) Typeand the type of expressionmay only differ with Their cast is resolved at compile time. Why does a template have to be declared before every function that uses one? Since the problem is probably with me, I'd like to change my thinking. A single const_cast expression const_cast can be used in programs that have any object with some constant value which need to be changed occasionally at some point. Not the answer you're looking for? How to declare a pointer to pointer to constant in C++? Another way is implement the iterator as a template, iterator_impl<> and then add two typedef s: using iterator = iterator_impl<value_type>; using const_iterator = iterator_impl<const value_type>; I'm trying to state my intent of not modifying the ptree in my code. If you must you can use const_cast to add constness, but removing it is so dangerous that this should be looked at as breaking code. dentry isn't const, but dentry->d_name.name is, so we match the const case and the compiler emits a warning. Connect and share knowledge within a single location that is structured and easy to search. is undefined. In particular, only const_cast may be used to cast away (remove) constness or volatility. 2 const_cast [] 6 C ++const_cast - ipjqi* pj* q Looking at the C++ new[] cookie. T* converts implicitly to const T*. consecutive > tokens. using: #define CONST_CAST (typename,value) \. A version of Chandas.ttf found on some Chrome bots has 660kb of GPOS, mostly junk. One way is to implement the bulk in const_iterator and to let iterator inherit from that. Is using increment (operator++) on floats bad style? I thought a good design decision would be to declare the parameter according to that source buffer fully const. How to get a non-const iterator while using a const "this" pointer? Powered by CNET. . A const static variable (global variable or static local variable) is a constant, and may be used for data like mathematical constants, such as double const PI = 3.14159 - realistically longer, or overall compile-time parameters. You should not use const_cast to add const because. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. In particular, only const_cast may be used to cast away (remove) constness or volatility. Can we keep alcoholic beverages indefinitely? unless Type is a reference type. You _could_ do. Actually, I am. A const_cast operator is used to add or remove a const or volatile modifier The const_cast operator (C++ only) A const_cast operator is used to add or remove a const or volatile modifier to or from a type. Why is my window losing its HTMEME when I call SetWindowLongPtr(GWL_STYLE) on it? casting away the constness using const_cast. This can be useful if it is necessary to add/remove constness from a variable.static_castThis is used for the normal/ordinary type conversion. In the cases where it is required to add const, its use is dangerous in hard to reason about ways. It is unnecessary. , const const_cast const " " const const const const How portable is this code? Can I cast a derived class to a private base class, using C-style cast? To learn more, see our tips on writing great answers. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Adding/Removing const qualifier with const_cast. It can strip volatile, or make you miss the fact that const was added somewhere else in your variables and your const_cast now silently strips them. feature, you may specify a template_id as Type in the const_cast. (since const can be cast away), Using git for VS2010 project: Can't add file *.opensdf. Why would I make copy constructor and assignment operator private and implemented in C++? *PATCH v1] read-cache: speed up index load through parallelization @ 2018-08-23 15:41 Ben Peart 2018-08-23 17:31 ` Stefan Beller ` (8 more replies) 0 siblings, 9 replies; 199+ messages in thread From: Ben Peart @ 2018-08-23 15:41 UTC (permalink / raw) To: git; +Cc: 106 Chapter 15. Syntax The syntax is as follows I don't think there's a way to key off the constness of dentry instead of dentry->d_name.name, so I've gone with the following for now. Error in makefile: multiple definition of _start. * [PATCH v2 1/4] container_of: add container_of_const() that preserves const-ness of the pointer @ 2022-12-05 12:12 Greg Kroah-Hartman 2022-12-05 12:12 ` [PATCH v2 2/4] device.h: move kobj_to_dev() to use container_of_const() Greg Kroah-Hartman ` (5 more replies) 0 siblings, 6 replies; 16+ messages in thread From: Greg Kroah-Hartman @ 2022-12 . For my use case I have a function that copies data (bytes) from a non-const source buffer. There are cases where you need to call const_cast in order to add const that will not happen implicitly. It can do something you don't want it to do. Using const_cast to add const-ness - bad idea? Dec 5, 2022, 6:15 AM Post #2 of 11 (12 views) Any disadvantage of using const reference when iterating over basic types? Dual EU/US Citizen entered EU on US Passport. . Aha! not been declared const, but you cannot modify this So here's over-simplified version of what I'm trying to do: (NB: If you are a system administrator and have no idea what this message is talking about, this may indicate a serious mail system misconfiguration somewhere. If you had written it the other way around: int& MyClass::operator [] (int index) { return const_cast<int&> (const_cast<MyClass const&> (*this) [index]); } This is better. API reference; Downloads; Samples; Support The const_cast doesn't make it safer, it just hides the error. Less obvious, I think, is that Squares are not Rectangles @Yakk boost::optional = get_child_optional(PATH); fails for the same reason in my code, as far as I can make out. Solution 1. reinterpret_cast changes the interpretation of the data within the object.const_cast adds or removes the const qualifier. With the right angle bracket If a pointer to T1 can be converted to a pointer to This is a specific case of the rectangle-square problem. In particular, only const_cast may be used to cast away (remove) constness or volatility. So in this case the const_cast would only be a necessary evil to enable to function call and not willfully remove the const-ness of a pointer You should not use const_cast to add const, because: it's unnecessary. I . How can I use a VPN to access a Russian website that is banned in the EU? Why is including "using namespace" into a header file a bad idea in C++? cout << "i: " << i << endl; cout . Using const_cast to add const-ness - bad idea? All rights reserved. So while const_cast is required to make the assign_ptr call compile, it is because it was unsafe. What does " const X* p " mean? C pointers : pointing to an array of fixed size. 2) lvalue of any type T may be converted to a lvalue or rvalue reference to the same type T, more or less cv-qualified. As I've discovered, const_cast may be used not only to remove, but also to add constness to type. a member declared explicitly const. (Note that immutable Squares are a kind of immutable Rectangle; it is the mutation that causes the issue. Your question states that char sourcebuffer[] = {0x00}; copyfunction(sourcebuffer); is an error, but that's not true. In this case, the result is an lvalue. clang: warning: argument unused during compilation: '-stdlib=libc++', How can I initialize objects in a dynamically allocated array with some arguments. This isn't something I've encountered before. Cancelling a thread using pthread_cancel : good practice or bad, How to pass const pointer to const object using unique_ptr, Is const a lie? Variables marked as const using structured bindings are not const, How much bad can be done using register variables in C++. I am looking for the "cleanest" way to cast away the constness of a. pointee in C89, something like const_cast<T*> () in C++. *PATCH] PR c++/80544 strip cv-quals from cast results @ 2017-04-27 18:02 Jonathan Wakely 2017-04-27 18:55 ` Paolo Carlini ` (2 more replies) 0 siblings, 3 replies; 25+ messages in thread From: Jonathan Wakely @ 2017-04-27 18:02 UTC (permalink / raw) To: gcc-patches [-- Attachment #1: Type: text/plain, Size: 578 bytes --] This is probably not the best way to do this, but it seems to work. As with all cast expressions, the result is: Pointers to functions and pointers to member functions are not subject to const_cast. const_cast is dangerous because it makes it impossible for the C++ type system to prevent you from trying to modify a const object. This is a specific case of the rectangle-square problem. Possible implementation template <class T > constexpr std::add_const_t< T >& as_const ( T & t) noexcept { return t; } Notes Feature-test macro __cpp_lib_as_const Example Run this code object through b1. of b1 and modify the value to which it refers. modify it, the results are undefined. This is also the cast responsible for implicit type coersion and can also be called explicitly. Only the following conversions can be done with const_cast. Why is "using namespace std;" considered bad practice? How to use SQLite in C++ program using Code::Blocks? In the upcoming commits, I'll be speeding that up by optimizing add_sorted_array(), while also reducing work by rejecting out-of-sort arrays quickly and propagate the rejection. SE DMA mode can be used for larger transfers and FIFO mode for smaller transfers. How do we know the true value of a parameter, in order to check estimator properties? Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. Hi, what about add const-ness to call const class function? mainconst int . Types cannot be defined within const_cast. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Why do you need to explicitly cast it? been explicitly declared as const, and attempt to A const_cast operator adds or removes a const or volatile modifier to or from a type. Are the S&P 500 and Dow Jones Industrial Average securities? Doing so results in undefined behavior. Is it a good idea to return " const char * " from a function? This is also the cast responsible for implicit type coersion and can also be called explicitly. Here we use const_cast to call a function that is not const-correct. It means p points to an object of class X, but p can't be used to change that X object (naturally p could also be NULL ). This means that you claim that the problem has been dealt with. In this case, the result is Home . In the cases where the operation is safe, it is almost always not required. The result of a const_castexpression is an rvalue unless Typeis a reference type. The const_cast doesn't make it safer, it just hides the error. Find centralized, trusted content and collaborate around the technologies you use most. Is it cheating if the proctor gives a student the answer key by mistake and the student doesn't report it? You should not use const_cast to add const, because: it's unnecessary. A side effect of it is that modification of *bar is undefined behavior, as it modifies a variable declared const (it makes bar, a int*, point at foo a const int). it's potentially (albeit unlikely) harmful. If this is not the case it is now your responsibility to reopen the Bug report if necessary, and/or fix the problem forthwith. const_castcan be used to remove or add const to a variable. (Note that immutable Squares are a kind of immutable Rectangle; it is the mutation that causes the issue. const_cast<double&> (x) = somePoint->x; But still, you have to answer this question: why did you make the member. T2 casts away constness, the following types of conversions also cast Thanks for contributing an answer to Stack Overflow! can be used to remove or add const to a variable. const_cast operator syntax >>-const_cast--<-- Type -->-- (-- expression --)-------------------->< Type and the type of expression may only differ with respect to their const and volatile qualifiers. How many transistors at minimum do you need to build a general-purpose computer? Some const_cast s is bound to be required. Their cast is resolved at compile time. const cast const cast . Are defenders behind an arrow slit attackable? A const_cast operator is used to add or remove a const or volatile modifier to or from a type. Laurent Deniau. Why is the keyword "typename" needed before qualified dependent names, and not before qualified independent names? You should not use const_cast to add const because. C++ read and compare magic number from file, std::for_each usage on member function with two args. Squares are not Rectangles, because if you change the width of a Square its height also changes, and this does not happen when you modify a Rectangle. Types III: Conversions Another place is with explicit pointer changes, if you don't want to use an intervening void*, but these are also pretty uncommon: long x = 3490; long * p = & x; unsigned char * c = (unsigned char *) p; A third place it's often required is with the character conversion functions in <ctype.h> where you should cast questionably-signed values to unsigned . A side effect of it is that modification of *bar is undefined behavior, as it modifies a variable declared const (it makes bar, a int*, point at foo a const int). The rubber protection cover does not pass through the hole in the rim. int* turns into a const int* implicitly. [PATCH v2 1/4] container_of: add container_of_const() that preserves const-ness of the pointer [ In reply to] rafael at kernel. So while const_cast is required to make the assign_ptr call compile, it is because it was unsafe. a constant may be more suitable than a variable if the value will never change, because it may both enable the compiler to produce better code (knowing that a certain multiplication is always by two instead of an arbitrary value will almost certainly result in faster code) and programmers to understand it faster as they don't have to watch for const. For a function call like below this would lead to a pointer-type error 'const char* const <-> char*'. const_cast But changes when calling an external function, still prints the old value in the main (where const int is initialized first). Why using static namespace/class member variables is a bad idea in C++? What's the right approach? So it make sense that you can only find code snipets of const_cast where it is used to remove const-ness. (Well, not all rectangles, anyway.) Similarly, int** are not int const**. Template parameters T A type. LKML Archive on lore.kernel.org help / color / mirror / Atom feed * [PATCH v2 1/4] container_of: add container_of_const() that preserves const-ness of the pointer @ 2022-12-05 12:12 Greg Kroah-Hartman 2022-12-05 12:12 ` [PATCH v2 2/4] device.h: move kobj_to_dev() to use container_of_const() Greg Kroah-Hartman ` (5 more replies) 0 siblings, 6 replies; 16+ messages in thread From: Greg Kroah . How do you add a repeated field using Google's Protocol Buffer in C++? 2) lvalue of any type T may be converted to a lvalue or rvalue reference to the same type T, more or less cv-qualified. Doing so results in undefined behavior. It can remove volatile from the pointer type, which is not the intention here and would result in undefined behavior if sourcebuffer were declared as volatile sourcebuffer[]. Notice that this class merely obtains a type using another type as model, but it does not transform values or objects between those types. as we all know the usage of const_cast to remove the const-ness of a pointer should be avoided. . Copyright 2022 www.appsloveworld.com. Mathematica cannot find square roots of some matrices? const_cast operator syntax >>-const_cast--<-- Type -->-- (-- expression --)-------------------->< Type and the type of expression may only differ with respect to their const and volatile qualifiers. In the section above we have seen that we can have a const pointer or a const reference that points to a non-const object, the other way around isn't possible.. Now, if you have scenarios where you need to modify the constness, either way, you can use const_cast. const_cast is one of the type casting operators. The static_cast operator cannot be used to cast away const.You can use static_cast to cast "down" a hierarchy (from a base to a derived pointer or reference), but the conversion is not checked; the result might not be usable. The dynamic_cast operator can also be used to perform a "cross cast." 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