const_cast conversion
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Convertidos entre os tipos com diferentes cv-qualificação.
Original:
Converts between types with different cv-qualification.
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[editar] Sintaxe
const_cast < new_type > ( expression )
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Retorna um valor de
new_type tipo.Original:
Returns a value of type
new_type.The text has been machine-translated via Google Translate.
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[editar] Explicação
Apenas as conversões que se seguem podem ser feitas com const_cast. Em particular, apenas const_cast pode ser usado para jogar fora (remover) constness ou volatilidade.
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)
Dois ponteiros, possivelmente em vários níveis para o mesmo tipo podem ser convertidas entre si, independentemente do CV-eliminatórias em cada nível.
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 de qualquer
T tipo pode ser convertida para uma referência lvalue ou rvalue ao T mesmo tipo, mais ou menos cv-qualificado. Da mesma forma, um rvalue pode ser convertida para uma referência rvalue mais ou menos cv qualificado.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)
Mesmas regras se aplicam aos ponteiros possivelmente a vários níveis como membros de dados.
Original:
Same rules apply to possibly multilevel pointers to data members.
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4)
valor de ponteiro nulo pode ser convertido para o valor de ponteiro nulo new_type
Original:
null pointer value may be converted to the null pointer value of new_type
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Tal como acontece com todas as expressões fundido, o resultado é:
Original:
As with all cast expressions, the result is:
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- um lvalue se new_type é um tipo de referência ou uma referência lvalue rvalue a funcionar 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. - um xValue se new_type é uma referência para rvalue tipo de objeto;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. - uma outra forma prvalue.Original:a prvalue otherwise.The text has been machine-translated via Google Translate.
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[editar] Notas
Ponteiros para funções e ponteiros para as funções de membro não estão sujeitos a const_cast
Original:
Pointers to functions and pointers to member functions are not subject to const_cast
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Mesmo que const_cast pode remover constness de qualquer ponteiro ou referência, usando o ponteiro resultante ou referência a escrever para um objeto que foi declarado const invoca comportamento indefinido.
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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[editar] Palavras-chave
[editar] Exemplo
#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 }
Saída:
i = 4 type::i = 4
