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Declaring functions

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Allgemeine Themen
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General topics
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Flusskontrolle
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Flow control
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Bedingte Ausführung Aussagen
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Conditional execution statements
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Iterationsanweisungen
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Iteration statements
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Gehe Aussagen
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Jump statements
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Funktionen
Original:
Functions
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Funktion Erklärung
Lambda-Funktion Erklärung
Funktions-Template
inline-Spezifizierer
Exception-Spezifikationen (veraltet)
noexcept Spezifizierer (C++11)
Ausnahmen
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Exceptions
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Namespaces
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Namespaces
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Types
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Types
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union-Typen
Funktionstypen
decltype specifier (C++11)
Specifiers
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Specifiers
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cv Planer
Lagerdauer Planer
constexpr Spezifizierer (C++11)
auto Spezifizierer (C++11)
alignas Spezifizierer (C++11)
Initialisierung
Original:
Initialization
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Literale
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Literals
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Expressions
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Expressions
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alternative Darstellungen
Utilities
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Utilities
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Types
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Types
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typedef declaration
Typ Aliasdeklaration (C++11)
Attribute (C++11)
Wirft
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Casts
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impliziten Konvertierungen
const_cast conversion
static_cast conversion
dynamic_cast conversion
reinterpret_cast conversion
C-Stil und funktionale Besetzung
Speicherzuweisung
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Memory allocation
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Classes
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Classes
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Class-spezifische Funktion Eigenschaften
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Class-specific function properties
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explizit (C++11)
statisch
Besondere Member-Funktionen
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Special member functions
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Templates
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Templates
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Klassen-Template
Funktions-Template
Template-Spezialisierung
Parameter Packs (C++11)
Verschiedenes
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Miscellaneous
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Inline Montage
 
Eine Funktion Deklaration führt den Namen der Funktion und ihren Typ. Es kann in jedem Bereich erscheinen, und wird häufig in Header-Dateien platziert werden .
Original:
A function declaration introduces the function name and its type. It may appear in any scope, and is commonly placed in header files.
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ret name ( params ) ; (1)
ret name ( params ) cv ref except attr ; (2)
auto name ( params ) cv ref except attr -> ret ; (3) (seit C++11)
Eine Funktionsdefinition versorgt den Körper einer Funktion. Es darf nur in Namespace oder Gültigkeitsbereich der Klasse erscheinen .
Original:
A function definition provides the body of a function. It may only appear in namespace or class scope.
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decl name ( params ) { body } (4)
attr decl name ( params ) cv ref except attr virt try init-list { body } catch (5)
attr decl name ( params ) cv ref except attr -> ret virt try init-list { body } catch (6) (seit C++11)
attr decl name ( params ) cv ref except attr virt = 0 ; (7)
attr decl name ( params ) cv ref except attr virt = default ; (8) (seit C++11)
attr decl name ( params ) cv ref except attr virt = delete ; (9) (seit C++11)

[Bearbeiten] Erklärung

1)
Typische Funktion Erklärung
Original:
Typical function declaration
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2)
Umfassende Funktion Erklärung
Original:
Comprehensive function declaration
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3)
Umfassende Funktion Erklärung mit nachgestellten Rückgabetyp
Original:
Comprehensive function declaration with trailing return type
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4)
Typische nicht-Member-Funktion Definition
Original:
Typical non-member function definition
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5)
Umfassende Definition der Funktion
Original:
Comprehensive function definition
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6)
Umfassende Definition der Funktion mit nachgestellten Rückgabetyp
Original:
Comprehensive function definition with trailing return type
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7)
Rein virtuelle Memberfunktion
Original:
Pure virtual member function
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8)
Defaulted Member-Funktion
Original:
Defaulted member function
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9)
Deleted Member-Funktion
Original:
Deleted member function
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attr(C++11) -
Optional Sequenz von einer beliebigen Anzahl von Funktion Attribute wie [[noreturn]] oder [[carries_dependency]]. Kann sowohl vor als auch nach dem Namen der Funktion angezeigt
Original:
Optional sequence of any number of Funktion Attribute, such as [[noreturn]] or [[carries_dependency]]. May appear both before and after the function name
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ret -
die Art von der Funktion zurückgegeben, kann void sein, wenn die Funktion nichts. Kann kein Array oder eine Funktion Typ sein kann, obwohl ein Zeiger oder Verweis auf solche sein. Erforderlich für alle Funktionen mit Ausnahme der Konstruktoren, Destruktoren und Umwandlung Betreiber, die nicht bereitstellen muss einen Rückgabetyp .
Original:
the type returned by the function, may be void if the function returns nothing. Cannot be array or function type, although can be a pointer or reference to such. Required for all functions except constructors, destructors, and conversion operators, which must not provide a return type.
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decl -
Erklärung specifier Sequenz, die von keiner oder einer der folgenden Suchbegriffe besteht: static, extern, inline, virtual, explicit, friend, constexpr, kombiniert mit dem Rückgabetyp, ret
Original:
declaration specifier sequence, which consists of none or some of the following keywords: static, extern, inline, virtual, explicit, friend, constexpr, combined with the return type, ret
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{{par | cv |{{tr| Optional const, volatile oder const volatile, nur für nicht-statische Member-Funktionen. Für eine Member-Funktion der Klasse T, die Art der [[cpp / Sprache / dieser| Optional const, volatile, or const volatile, only applicable to non-static member functions. For a member function of class T, the type of the [[cpp/language/this}}|this pointer]] will be const T*, volatile T*, or const volatile T* respectively. A member function declared const cannot modify members of *this.}}

ref(C++11) -
Optional & oder &&, nur für nicht-statische Member-Funktionen außer Konstruktoren oder Destruktoren. Für eine Member-Funktion der Klasse T, wird der Typ des impliziten Objekt-Parameter für die Zwecke der Überladungsauflösung sein T& oder T&& jeweils: a && qualifizierte Member-Funktion kann nur auf einem rvalue Objekt Ausdruck aufgerufen werden
Original:
Optional & or &&, only applicable to non-static member functions other than constructors or destructors. For a member function of class T, the type of the implicit object parameter for the purpose of overload resolution will be T& or T&& respectively: a &&-qualified member function can only be called on an rvalue object expression
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except -
entweder Dynamik-exception-Spezifikation oder noexcept-Spezifikation
Original:
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virt(C++11) -
Optional override oder final, nur für nicht-statische Member-Funktionen
Original:
Optional override or final, only applicable to non-static member functions
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->ret(C++11) -
Trailing Rückgabetyp, nur anwendbar, wenn ret ist auto. Sinnvoll, wenn der Typ hängt von Argumentnamen wie template <class T, class U> auto add(T t, U u) -> decltype(t + u); oder ist kompliziert, wie in auto fpif(int)->int(*)(int)
Original:
Trailing return type, only applicable if ret is auto. Useful if the type depends on argument names, such as template <class T, class U> auto add(T t, U u) -> decltype(t + u); or is complicated, such as in auto fpif(int)->int(*)(int)
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init-list -
Constructor Initialisierungsliste nur in Konstruktoren verwendet
Original:
Constructor Initialisierungsliste, only used in constructors
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try -
Optionale Funktion try-Block. Falls vorhanden, muss catch vorgesehen sein
Original:
Optional function try block. If present, catch must be provided
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catch -
Optionale Folge von catch-Blöcke ist nur anwendbar, der try verwendet .
Original:
Optional sequence of catch-Blöcke, only applicable of try is used.
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body -
Der Körper der Funktion, eine (möglicherweise leere) zusammengesetzten Anweisung
Original:
The body of the function, a (possibly empty) compound statement
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params -
Die Liste der Parameter
Original:
The list of parameters
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[Bearbeiten] Beispiel 1: Nicht-Member-Funktionen

#include <iostream>
#include <string>
 
// declaration in namespace(file) scope
// (the definition is provided later)
int f1();
 
// simple function with a default argument, returning nothing
void f0(const std::string& arg = "world") {
    std::cout << "Hello, " << arg << '\n';
}
 
// function returning a pointer to f0
auto fp11() -> void(*)(const std::string&) {
    return f0;
}
 
// function returning a pointer to f0, pre-C++11 style
void (*fp03())(const std::string&) {
    return f0;
}
 
int main()
{
    f0();
    fp11()("test");
    fp03()("again");
    int f2(std::string); // declaration in function scope
    std::cout << f2("bad12") << '\n';
}
 
// simple non-member function returning int
int f1() {
    return 42;
}
 
// function with an exception specification and a function try block
int f2(std::string str) noexcept try { 
    return std::stoi(str);
} catch(const std::exception& e) {
    std::cerr << "stoi() failed!\n";
    return 0;
}

Output:

Hello, world
Hello, test
Hello, again
stoi() failed!
0


[Bearbeiten] Beispiel 2: Member-Funktionen

#include <iostream>
#include <string>
#include <utility>
#include <exception>
 
struct S {
    int data;
 
    // simple converting constructor (declaration)
    S(int val);
 
    // simple explicit constructor (declaration)
    explicit S(std::string str);
 
    // const member function (definition)
    virtual int getData() const { return data; }
 
};
 
// definition of the constructor
S::S(int val) : data(val) {
    std::cout << "ctor1 called, data = " << data << '\n';
}
 
// this constructor has a catch clause
S::S(std::string str) try : data(std::stoi(str)) {
    std::cout << "ctor2 called, data = " << data << '\n';
} catch(const std::exception&) {
    std::cout << "ctor2 failed, string was '" << str << "'\n";
    throw; // ctor's catch clause should always rethrow
}
 
struct D : S {
    int data2;
    // constructor with a default argument
    D(int v1, int v2 = 11) : S(v1), data2(v2) {}
 
    // virtual member function
    int getData() const override { return data*data2; }
 
    // lvalue-only assignment operator
    D& operator=(D other) & {
        std::swap(other.data, data);
        std::swap(other.data2, data2);
        return *this;
    }
};
 
int main()
{
    D d1 = 1;
    S s2("2");
    try {
         S s3("not a number");
    } catch(const std::exception&) {}
    std::cout << s2.getData() << '\n';
 
   D d2(3, 4);
   d2 = d1; // OK: assignment to lvalue
//   D(5) = d1; // ERROR: no suitable overload of operator=
}

Output:

ctor1 called, data = 1
ctor2 called, data = 2
ctor2 failed, string was 'not a number'
2
ctor1 called, data = 3