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zero initialization

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C++
 
Linguagem C++
Tópicos gerais
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General topics
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Controle de fluxo
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Flow control
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Declarações execução condicional
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Conditional execution statements
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Instruções de iteração
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Iteration statements
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Ir declarações
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Jump statements
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Funções
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Functions
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declaração da função
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modelo de função
linha especificador
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Exceptions
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Tipos
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Types
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decltype specifier (C++11)
Especificadores
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Specifiers
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cv especificadores
armazenamento duração especificadores
constexpr especificador (C++11)
auto especificador (C++11)
alignas especificador (C++11)
Inicialização
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Initialization
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Literais
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Literals
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Expressões
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Expressions
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representações alternativas
Utilitários
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Utilities
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Tipos
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Types
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tipo de alias declaração (C++11)
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Conversões
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Casts
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conversões implícitas
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Alocação de memória
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Classes
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Classes
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Classe propriedades específicas de função
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Funções membro especiais
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Special member functions
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Modelos
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modelo de classe
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Diversos
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Miscellaneous
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Assembly embutido
 
Define o valor inicial de um objeto a zero
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Sets the initial value of an object to zero
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Índice

[editar] Sintaxe

static T object ; (1)
int () ; (2)
char array [ n ] = ""; (3)

[editar] Explicação

Zero inicialização é executada nas seguintes situações:
Original:
Zero initialization is performed in the following situations:
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1)
Para cada variável chamada com duração de armazenagem estática ou segmento local, antes de qualquer outra inicialização.
Original:
For every named variable with static or thread-local storage duration, before any other initialization.
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2)
Como parte do valor de inicialização seqüência para não-classe tipos e para os membros do Valor inicializados tipos de classes que não têm construtores.
Original:
As part of valor de inicialização sequence for non-class types and for members of value-initialized class types that have no constructors.
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3)
Quando uma matriz de caracteres é inicializado com uma string literal que é muito curto, o restante da matriz é inicializado com zero.
Original:
When a character array is initialized with a string literal that is too short, the remainder of the array is zero-initialized.
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Os efeitos de inicialização de zero são:
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The effects of zero initialization are:
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  • Se T é um tipo escalar, o valor inicial do objeto é o convertidos implicitamente de zero integrante constante para T.
    Original:
    If T is a scalar type, the object's initial value is the integral constant zero convertidos implicitamente to T.
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  • Se T é um tipo de classe não-união, todas as classes base e membros não-estáticos de dados são inicializado com zero, e todo estofamento é inicializado com zero bits. Os construtores, se houver, são ignorados.
    Original:
    If T is an non-union class type, all base classes and non-static data members are zero-initialized, and all padding is initialized to zero bits. The constructors, if any, are ignored.
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  • Se T é um tipo de união, o primeiro não-estático chamado membro de dados é inicializado com zero e todo estofamento é inicializado com zero bits.
    Original:
    If T is a union type, the first non-static named data member is zero-initialized and all padding is initialized to zero bits.
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  • Se T é tipo de matriz, cada elemento é inicializado com zero
    Original:
    If T is array type, each element is zero-initialized
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  • Se T é tipo de referência, nada é feito.
    Original:
    If T is reference type, nothing is done.
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[editar] Notas

As variáveis ​​estáticas e segmento local é o primeiro zero-inicializado e então inicializado novamente como especificado no programa, por exemplo, estática função local é o primeiro zero-inicializado no arranque do programa, e então seu construtor é chamado quando a função é primeiro entrou. Se a declaração de uma estática não-classe não tem inicializador, então a inicialização padrão não faz nada, deixando o resultado do início de zero-inicialização sem modificações.
Original:
The static and thread-local variables are first zero-initialized and then initialized again as specified in the program, e.g. a function-local static is first zero-initialized at program startup, and then its constructor is called when the function is first entered. If the declaration of a non-class static has no initializer, then default initialization does nothing, leaving the result of the earlier zero-initialization unmodified.
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Um ponteiro inicializado com zero é o valor de ponteiro nulo do seu tipo, mesmo que o valor do ponteiro nulo não é zero integrante.
Original:
A zero-initialized pointer is the null pointer value of its type, even if the value of the null pointer is not integral zero.
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[editar] Exemplo

#include <string>
 
double f[3]; // zero-initialized to three 0.0's
int* p;   // zero-initialized to null pointer value
std::string s; // zero-initialized to indeterminate value
               // then default-initialized to ""
int main(int argc, char* argv[])
{
    static int n = argc; // zero-initialized to 0
                         // then copy-initialized to argc
    delete p; // safe to delete a null pointer
}


[editar] Veja também

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