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static_cast conversion

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static_cast conversion
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Convertidos entre os tipos usando uma combinação de conversões implícitas e definidos pelo usuário.
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Converts between types using a combination of implicit and user-defined conversions.
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Índice

[editar] Sintaxe

static_cast < new_type > ( expression )
Retorna um valor de new_type tipo.
Original:
Returns a value of type new_type.
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[editar] Explicação

Apenas as seguintes conversões podem ser feitas com static_cast, excepto quando essas conversões seria lançado fora constness''' ou volatilidade.
Original:
Only the following conversions can be done with static_cast, except when such conversions would cast away constness or volatility.
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1)
Se um objeto temporário de new_type tipo pode ser declarada e inicializada com expression, como por new_type Temp(expression);, que pode envolver conversões implícitas, uma chamada para o construtor de new_type ou uma chamada para um operador definido pelo usuário conversão, então static_cast<type>(expression) calcula e retorna o valor do objeto temporário.
Original:
If a temporary object of type new_type can be declared and initialized with expression, as by new_type Temp(expression);, which may involve implicit conversions, a call to the constructor of new_type or a call to a user-defined conversion operator, then static_cast<type>(expression) computes and returns the value of that temporary object.
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2)
Se new_type é um ponteiro ou referência a alguns D classe e o tipo de expression é um ponteiro ou referência a sua base não-virtual B, static_cast executa uma' abatido. static_cast tal, não faz verificações de tempo de execução para garantir que tipo de tempo de execução do objeto é realmente D, e só pode ser usado com segurança se essa condição é garantida por outros meios, como na implementação polimorfismo estático. Abatida seguro pode ser feito com dynamic_cast.
Original:
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 polimorfismo estático. Safe downcast may be done with dynamic_cast.
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3)
Se new_type é um tipo de referência rvalue, static_cast converte o valor de expression para xValue. Este tipo de static_cast é usada para implementar a semântica de se mover em std::move. (a partir do C++ 11)
Original:
If new_type is an rvalue reference type, static_cast converts the value of expression to xvalue. This type of static_cast is used to implement move semantics in std::move. (a partir do C++ 11)
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4)
Se new_type é o tipo void (possivelmente cv qualificado), static_cast descarta o valor de expression depois avaliá-lo.
Original:
If new_type is the type void (possibly cv-qualified), static_cast discards the value of expression after evaluating it.
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5) new_type com o tipo de expression existe, que não inclui lvalue-a-rvalue, array para ponteiro, função para-ponteiro, ponteiro nulo, membro ponteiro nulo, ou conversão boolean, então static_cast pode realizar o inverso do que a conversão implícita.
Original:
If an
conversão implícita
Original:
implicit conversion
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</div>
sequence from new_type to the type of expression exists, that does not include lvalue-to-rvalue, array-to-pointer, function-to-pointer, null pointer, null member pointer, or boolean conversion, then static_cast can perform the inverse of that implicit conversion.
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6)
Se a conversão de expression new_type envolve lvalue para rvalue, matriz-to-ponteiro, ou uma função-para-ponteiro de conversão, pode ser realizado por explicitamente static_cast.
Original:
If conversion of expression to new_type involves lvalue-to-rvalue, array-to-pointer, or function-to-pointer conversion, it can be performed explicitly by static_cast.
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7)
Tipo de enumeração escopo pode ser convertido para um tipo inteiro ou de ponto flutuante. (a partir do C++ 11)
Original:
Scoped enumeration type can be converted to an integer or floating-point type. (a partir do C++ 11)
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8)
Tipo, um número inteiro de ponto flutuante, ou enumeração pode ser convertido para qualquer tipo de enumeração (o resultado não é especificado, se o valor de expression, convertido para o tipo subjacente da enumeração, não é um dos valores de enumeração de destino)
Original:
Integer, floating-point, or enumeration type can be converted to any enumeration type (the result is unspecified if the value of expression, converted to the enumeration's underlying type, is not one of the target enumeration values)
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9)
Um ponteiro para membro de alguma D classe pode ser upcast para um ponteiro para membro do seu B classe base. Este static_cast não faz verificações para garantir o membro realmente existe no tipo de tempo de execução do objeto pontiagudo para.
Original:
A pointer to member of some class D can be upcast to a pointer to member of its base class B. This static_cast makes no checks to ensure the member actually exists in the runtime type of the pointed-to object.
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10)
Um ponteiro de tipo de prvalue para void (possivelmente cv qualificado) pode ser convertido para qualquer tipo de ponteiro. Conversão de qualquer ponteiro para ponteiro para anular e voltar para ponteiro para o tipo (ou mais cv qualificado) original preserva seu valor original.
Original:
A prvalue of type pointer to void (possibly cv-qualified) can be converted to pointer to any type. Conversion of any pointer to pointer to void and back to pointer to the original (or more cv-qualified) type preserves its original value.
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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;
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  • 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;
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  • uma outra forma prvalue.
    Original:
    a prvalue otherwise.
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[editar] Notas

static_cast também pode ser utilizado para resolver a ambiguidade sobrecargas de função, realizando uma função de conversão-para-ponteiro de tipo específico, como em std::transform(s.begin(), s.end(), s.begin(), static_cast<int(*)(int)>(std::toupper));
Original:
static_cast may also be used to disambiguate function overloads by performing a function-to-pointer conversion to specific type, as in std::transform(s.begin(), s.end(), s.begin(), static_cast<int(*)(int)>(std::toupper));
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[editar] Palavras-chave

static_cast

[editar] Exemplo

#include <vector>
#include <iostream>
 
struct B {};
struct D : B {};
 
enum class E { ONE, TWO, THREE };
enum EU { ONE, TWO, THREE };
 
int main()
{
    // 1: initializing conversion
    int n = static_cast<int>(3.14); 
    std::cout << "n = " << n << '\n';
    std::vector<int> v = static_cast<std::vector<int>>(10);
    std::cout << "v.size() = " << v.size() << '\n';
 
    // 2: static downcast
    D d;
    B& br = d; // upcast via implicit conversion
    D& another_d = static_cast<D&>(br); // downcast
 
    // 3: lvalue to xvalue
    std::vector<int> v2 = static_cast<std::vector<int>&&>(v);
    std::cout << "after move, v.size() = " << v.size() << '\n';
 
    // 4: discarded-value expression
    static_cast<void>(v2.size());
 
    // 5. inverse of implicit conversion
    // todo
 
    // 6. array-to-pointer followed by upcast
    D a[10];
    B* dp = static_cast<B*>(a);
 
    // 7. scoped enum to int or float
    E e = E::ONE;
    int one = static_cast<int>(e);
 
    // 8. int to enum, enum to another enum
    E e2 = static_cast<E>(one);
    EU eu = static_cast<EU>(e2);
 
    // 9. pointer to member upcast
    // todo
 
    // 10. void* to any type
    void* voidp = &e;
    std::vector<int>* p = static_cast<std::vector<int>*>(voidp);
}

Output:

n = 3
v.size() = 10
after move, v.size() = 0

[editar] Veja também