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    direct initialization

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    C++
     
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    General topics
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    decltype specifier(C++11)
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    Specifiers
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    Initialisierung
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    Initialization
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    Casts
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    impliziten Konvertierungen
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    Inline Montage
     
    Initialisiert ein Objekt aus expliziten Satz Konstruktorargumente .
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    Initializes an object from explicit set of constructor arguments.
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    Inhaltsverzeichnis

    [Bearbeiten]Syntax

    Tobject( arg);

    Tobject( arg1, arg2, ...);

    		 (1)
    Tobject{ arg};

    Tobject{ arg1, arg2, ...};

    		 (2) (seit C++11)
    T( other)

    T( arg1, arg2, ...);

    		 (3)
    static_cast<T>(other) (4)
    newT(args, ...) (5)
    Class::Class() : member(args, ...) {... (6)
    [arg](){... (7) (seit C++11)

    [Bearbeiten]Erklärung

    Direkter Initialisierung in den folgenden Situationen durchgeführt:
    Original:
    Direct initialization is performed in the following situations:
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    1)
    Initialisierung mit einer nichtleeren geklammerten Liste von Ausdrücken
    Original:
    initialization with a nonempty parenthesized list of expressions
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    2)
    während list-Initialisierung Sequenz, wenn keine Initialisierer-Liste constuctors vorgesehen sind und ein passender Konstruktor zugänglich ist, und alle notwendigen impliziten Konvertierungen sind nicht Verengung .
    Original:
    during list-Initialisierung sequence, if no initializer-list constuctors are provided and a matching constructor is accessible, and all necessary implicit conversions are non-narrowing.
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    3)
    Initialisierung eines prvalue vorübergehend durch funktionale Besetzung oder mit einem geklammerten Ausdruck Liste
    Original:
    initialization of a prvalue temporary by funktionale Besetzung or with a parenthesized expression list
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    4)
    Initialisierung eines prvalue temporären durch eine static_cast expession
    Original:
    initialization of a prvalue temporary by a static_cast expession
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    5)
    Initialisierung eines Objekts mit dynamischen Lagerdauer von einem neuen Ausdruck mit einem nicht-leeren Initialisierung
    Original:
    initialization of an object with dynamic storage duration by a new-expression with a non-empty initializer
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    6)
    Initialisierung einer Base oder eines nicht-statische Element durch constructor Initialisierungsliste
    Original:
    initialization of a base or a non-static member by constructor Initialisierungsliste
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    7)
    Initialisierung der Schließung Objekt Mitglieder aus den Variablen durch Kopie in einem Lambda-Ausdruck gefangen
    Original:
    initialization of closure object members from the variables caught by copy in a lambda-expression
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    Die Auswirkungen der direkten Initialisierung sind:
    Original:
    The effects of direct initialization are:
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    • Wenn T eine Klasse Typ ist, sind die Konstrukteure von T untersucht und die beste Übereinstimmung wird durch Überlast Auflösung gewählt. Der Konstruktor wird dann aufgerufen, um das Objekt zu initialisieren .
      Original:
      If T is a class type, the constructors of T are examined and the best match is selected by overload resolution. The constructor is then called to initialize the object.
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    • Andernfalls, wenn T ein Nicht-Klasse-Typ ist, werden Standard-Konvertierungen verwendet, falls notwendig, um den Wert des an die other cv-uneingeschränkten Version T umzuwandeln .
      Original:
      Otherwise, if T is a non-class type, Standard-Konvertierungen are used, if necessary, to convert the value of other to the cv-unqualified version of T.
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    [Bearbeiten]Notes

    Direct-Initialisierung ist toleranter als copy-Initialisierung: copy-Initialisierung nur hält nicht explizit Konstruktoren und benutzerdefinierte Konvertierung Funktionen, während direkte Initialisierung berücksichtigt alle Konstrukteure und implizite Konvertierung Sequenzen .
    Original:
    Direct-initialization is more permissive than copy-initialization: copy-initialization only considers non-explicit constructors and user-defined conversion functions, while direct-initialization considers all constructors and implicit conversion sequences.
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    [Bearbeiten]Beispiel

    #include <string>#include <iostream>#include <memory>   struct Foo {int mem;explicit Foo(int n): mem(n){}};   int main(){std::string s1("test");// constructor from const char*std::string s2(10, 'a');   std::unique_ptr<int> p(new int(1));// OK: explicit constructors allowed// std::unique_ptr<int> p = new int(1); // error: constructor is explicit   Foo f(2);// f is direct-initialized:// constructor parameter n is copy-initialized from the rvalue 2// f.mem is direct-initialized from the parameter n// Foo f2 = 2; // error: constructor is explicit   std::cout<< s1 <<' '<< s2 <<' '<<*p <<' '<< f.mem<<'\n';}

    Output: 

    test aaaaaaaaaa 1 2

    [Bearbeiten]Siehe auch

    Von „https://de.cppreference.com/mwiki/index.php?title=cpp/language/direct_initialization&oldid=27068“
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