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. A pointer converted to an integer of sufficient size and back to the same pointer type is guaranteed to have its original value, otherwise the resulting pointer cannot be dereferenced safely. I create a class Rectangle that contain width and length and calculate area. However it will affect how other CPU instructions are generated. If T2's alignment is not stricter than T1's, conversion to the original type yields the original value, otherwise the resulting pointer cannot be used safely. the value of b is not unspecified anymore in C++11 when using reinterpret_cast. Once a pointer is declared, you can refer to the thing it points to, known as the target of the pointer, by "dereferencing the pointer". Hi, I am just reading about reinterpret_cast<> unfortunately I don't understand much other than what I have stated below: reinterpret_cast allows any pointer to be converted into any other pointer type. char *ptr_my = 0; int *ptr_my_second = reinterpret_cast
(ptr_my); The reinterpret_cast is almost as dangerous as an “old fashion” cast. const int i= 3; // j is declared const int* p = const_cast(&i); *p = 4; // undefined behavior. Your code invokes Undefined Behavior (UB), and a likely output would be: k : 0x4e20 It is used when we want to work with bits. In the purpose of my homework, I learned pointer to function and lambda function. However, doing reinterpret_cast from char* to std::uint8_t* and then dereferencing the resulting pointer is a violation of strict aliasing rule and is undefined behavior if std::uint8_t is implemented as extended unsigned integer type. In the function foo we take an int* and a float*, in this example we call foo and set both parameters to point to the same memory location which in this example contains an int.Note, the reinterpret_cast is telling the compiler to treat the the expression as if it had the type specificed by its template parameter. Adjust the address of the pointer if necessary so that it will point to the D object. Then create a constant pointer, let us say “b” of the same data type and allocate it the address of our constant variable “a”. It conveniently cast any pointer type … You can use reinterpret_cast to cast any pointer or integral type to any other pointer or integral type. Reinterpret Cast. Segmentation fault It asks the compiler to treat the expression as if it has the new type. reinterpret_cast reinterpret_castcasts a pointer to any other type of pointer. It also allows casting from a pointer to an integer type and vice versa. This operator can cast pointers between non-related classed. The operation results is a simple binary copy of the value from one pointer to the other. reinterpret cast can cause problems when you convert pointers to data of one size to data of another. In the assembly code, you won’t see any CPU instructions corresponding to the reinterpret_cast call. It is used for reinterpreting bit patterns and is extremely low level. You don’t want to use std::function because it’s too heavy, for some sense of “heavy”. It simply converts the pointer type. So if you convert char * into int * then the compiler's going to be generating different instructions to read/write through those pointers so you can … struct Input { int a; int b; }; using Buffer = char[8]; The working draft of the standard (N4713) states regarding the usage of 8.5.1.10 Reinterpret cast The operation result is the simple binary copy of a value from one pointer to the other. error: reinterpret_cast from type const void*to type uv_loop_s*casts away qualifiers (clang ++) error: reinterpret_cast from const void *to uv_loop_s *constcasts away qualifiers. 4. reinterpret_cast. static_cast should be used when you want to cast from a numeric type to other, from a BaseClass* to a DerivedClass* or from a void* to a specific Type*. 2) If new_type is a pointer or reference to some class D and the type of expression is a pointer or reference to its non-virtual base B, static_cast performs a downcast.Such static_cast makes no runtime checks to ensure that the object's runtime type is actually D, and may only be used safely if this precondition is guaranteed by other means, such as when implementing static polymorphism. 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). This means that you could make a seemingly innocent and innocuous change to your … 2) If new_type is a reference or pointer to some class D and expression is lvalue of its non-virtual base B or prvalue pointer to it, static_cast performs a downcast. reinterpret_cast Type aliasing. In C and C++, constructs such as pointer type conversion and union — C++ adds reference type conversion and reinterpret_cast to this list — are provided in order to permit many kinds of type punning, although some kinds are not actually supported by the standard language. It can typecast any pointer to any other data type. Still I do not see the need of pointer at all. 1) const_cast can be used to change non-const class members inside a const member function. reinterpret_cast is intended for low-level casts that yield implementation-dependent and it would not be portable.. This is the most dangerous cast and should be used with care. So when can this come in handy ? Reinterpret Cast reinterpret_cast(expression) Used to: 1) Cast between incompatible types int* ptr = 0xDEADBEEF; int64_t x = reinterpret_cast(ptr); - types must be of same size - refuses to do float-integer conversions 10 reinterpret_cast, for casts between unrelated types such as a pointer type and an int. reinterpret_cast converts any pointer type to any other pointer type, even of unrelated classes. The reinterpret_cast operator can be used for conversions such as char* to int*, or One_class* to Unrelated_class*, which are inherently unsafe. Returns a value of type new_type.. Although a C-style cast appears to be a single cast, it can actually perform a variety of different conversions depending on context. It only provides some information for the compiler to generate code. reinterpret_cast converts between types by reinterpreting the underlying bit pattern. An object pointer (including void*) or function pointer can be converted to an integer type using reinterpret_cast. And given that the C++ standard is (1) defective (self-contradiction) and (2) reinterpret_cast will never change the memory layout. I understand that int-to-pointer conversion may involve widening, narrowing, or even more complex and possibly inexpressible semantics (segmented/non-linear memory architectures), but reinterpret_cast by definition is non-portable and error prone. You type intptr_t type & lt; Cstdint> If you want an integer type that is guaranteed to be in the form of indicator until that you can reinterpret_cast intptr_t from an indicator and then back safely. The operation results is a simple binary copy of the value from one pointer to the other. Explanation. reinterpret_cast. Common special cases for wanting to use a member function as a callback function are the window procedure and its cousin the dialog procedure. When 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 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 ADC initialize asks for 512 integers of type uint16_t but the pointer returned can only be uint8_t due to the library. I’m locked into the code in the PlainADC library. Perhaps you don’t like the fact that its copy constructor can throw. I want to retrieve my data as uint16_t via the pointer. Bit is long, but only to 32-bit long is the code to cast a pointer to return the pointer and the pointer loses the upper 32-bit value. Usage of the reinterpret_castoperator can have undefinedor implementation-dependent results. Suppose you want an object that can store a non-capturing lambda. The behavior of reinterpret_cast did not change, Windows did. In this article. — a reinterpret_cast, or — a reinterpret_cast followed by a const_cast, can be performed using the cast notation of explicit type conversion." 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 also allows casting from a pointer to an integer type and vice versa. C / C++ Forums on Bytes. #Reinterpret_cast. It's no different from casting to int. This can lead to dangerous situations: nothing will stop you from converting an int to an std::string*. To do: Re-interpreting an integer data type to an unsigned integer pointer using the C++ reinterpret_cast To show: Using the C++ reinterpret_cast, re-interpreting an int to unsigned int pointer in C++ programming // Using reinterpret_cast, int to unsigned int pointers conversion #include using namespace std; unsigned int* Test(int *q) using namespace std; unsigned int* Test (int *q) {. I see Timbo already pointed this out to you, and you said you would fix it, but four years later it remains incorrect. When a pointer or reference to object whose dynamic type is DynamicType is reinterpret_cast (or C-style cast) to a pointer or reference to object of a different type AliasedType, the cast always succeeds, but the resulting pointer or reference may only be used to access the object if one of the following is true: You will use reinterpret_cast in your embedded systems. Then create a third pointer, let us say “c” of data type int to be used for const_cast. It is conceivable that in C++ we might want to perform any of these three conversions. It would not check anything so it is the most dangerous cast. But the xp is only useful as an int*, which is truly a “reinterpretation” of the original X. We usually typecast the source pointer to its original type. The size of int has nothing to do with the size of a pointer, and it is not guaranteed (AFAICR!)
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