const_cast conversion
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Converte tra i tipi con diverse cv-qualificazione.
Original:
Converts between types with different cv-qualification.
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[modifica] Sintassi
const_cast < new_type > ( expression )
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Restituisce un valore di tipo
new_type.Original:
Returns a value of type
new_type.The text has been machine-translated via Google Translate.
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[modifica] Spiegazione
Solo le seguenti conversioni può essere fatto con const_cast. In particolare, solo const_cast può essere utilizzato per buttar via (rimuovere) constness o volatilità.
Original:
Only the following conversions can be done with const_cast. In particular, only const_cast may be used to cast away (remove) constness or volatility.
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1)
Due puntatori eventualmente multilivello stesso tipo possono essere convertiti tra loro, indipendentemente CV-qualificazione ad ogni livello.
Original:
Two possibly multilevel pointers to the same type may be converted between each other, regardless of cv-qualifiers at each level.
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2)
lvalue di qualsiasi tipo
T può essere convertito in un riferimento lvalue o rvalue al T stesso tipo, più o meno cv qualificati. Allo stesso modo, un rvalue può essere convertito in un più o meno cv qualificati riferimento rvalue.Original:
lvalue of any type
T may be converted to a lvalue or rvalue reference to the same type T, more or less cv-qualified. Likewise, an rvalue may be converted to a more or less cv-qualified rvalue reference.The text has been machine-translated via Google Translate.
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3)
Le stesse regole si applicano ai puntatori eventualmente multilivello ai membri di dati.
Original:
Same rules apply to possibly multilevel pointers to data members.
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4)
valore di puntatore nullo può essere convertito nel valore di puntatore nullo new_type
Original:
null pointer value may be converted to the null pointer value of new_type
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Come con tutti espressioni cast, il risultato è:
Original:
As with all cast expressions, the result is:
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- un lvalue se new_type è un tipo di riferimento o un riferimento lvalue rvalue un funzionamento tipo;Original:an lvalue if new_type is an lvalue reference type or an rvalue reference to function type;The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions. - un xValue se new_type è un riferimento rvalue per tipo di oggetto;Original:an xvalue if new_type is an rvalue reference to object type;The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions. - un prvalue altrimenti.Original:a prvalue otherwise.The text has been machine-translated via Google Translate.
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[modifica] Note
Puntatori a funzioni e puntatori a funzioni membro non sono soggetti a const_cast
Original:
Pointers to functions and pointers to member functions are not subject to const_cast
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Anche se const_cast può rimuovere constness da qualsiasi puntatore o un riferimento, utilizzando il puntatore risultante o il riferimento a scrivere a un oggetto che è stato dichiarato const richiama un comportamento indefinito.
Original:
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.
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[modifica] Parole chiave
[modifica] Esempio
#include <iostream> struct type { type() :i(3) {} void m1(int v) const { // this->i = v; // compile error: this is a pointer to const const_cast<type*>(this)->i = v; // OK } int i; }; int main() { int i = 3; // i is not declared const const int& cref_i = i; const_cast<int&>(cref_i) = 4; // OK: modifies i std::cout << "i = " << i << '\n'; type t; t.m1(4); std::cout << "type::i = " << t.i << '\n'; const int j = 3; // j is declared const int* pj = const_cast<int*>(&j); *pj = 4; // undefined behavior! void (type::*mfp)(int) const = &type::m1; // pointer to member function // const_cast<void(type::*)(int)>(mfp); // compiler error: const_cast does not // work on function pointers }
Output:
i = 4 type::i = 4
