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Range-based for loop (seit C++11)

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Führt eine for-Schleife über einen Bereich .
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Executes a for loop over a range.
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Betriebs über einen Bereich von Werten, zum Beispiel von einigen Behälter oder Liste .
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Used as a more readable equivalent to the traditional
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Inhaltsverzeichnis

[Bearbeiten] Syntax

for ( range_declaration : range_expression) loop_statement

[Bearbeiten] Erklärung

Die obige Syntax erzeugt Code ähnlich dem folgenden (__range, __begin und __end sind für die Ausstellung only):
Original:
The above syntax produces code similar to the following (__range, __begin and __end are for exposition only):
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{
auto && __range = range_expression ;
auto __begin = begin_expr(__range);
auto __end = end_expr(__range);
for (;__begin != __end; ++__begin) {
range_declaration = *__begin;
loop_statement
}

}

Die range_expression wird ausgewertet, um die Reihenfolge zu bestimmen oder den Bereich übernimmt iteriert werden. Jedes Element der Sequenz dereferenziert und übertragen auf die Variable mit dem Typ und den Namen in der range_declaration gegeben .
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The range_expression is evaluated to determine the sequence or range will be iterated over. Each element of the sequence is dereferenced, and assigned to the variable using the type and name given in the range_declaration.
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Die begin_expr und end_expr werden definiert, um entweder:
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The begin_expr and end_expr are defined to be either:
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  • (__range) und (__range + __bound) für Array-Typen, wo __bound ist das Array gebunden
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    (__range) and (__range + __bound) for array types, where __bound is the array bound
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  • begin(__range) und end(__range), die basierend auf Argument-Lookup Regeln gefunden. Für Standard-Containern endet es gleichwertig std::begin und std::end was wiederum Anrufe __range.begin() und __range.end() .
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    begin(__range) and end(__range), which are found based on argument-lookup rules. For standard containers this ends up being equivalent to std::begin and std::end which in turn calls __range.begin() and __range.end().
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Wenn eine vorübergehende range_expression zurückkehrt, wird die Lebensdauer bis zum Ende der Schleife verlängert, wie durch die Bindung an den R-Wert-Referenz __range angegeben .
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If range_expression returns a temporary, its lifetime is extended until the end of the loop, as indicated by binding to the rvalue reference __range.
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verwendet werden, um die Schleife frühzeitig verlassen und
continue-Anweisung
Original:
continue statement
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können verwendet werden, um die Schleife mit dem nächsten Element neu zu starten .

[Bearbeiten] Keywords

for

[Bearbeiten] Beispiel

#include <iostream>
#include <vector>
 
int main() 
{
    std::vector<int> v = {0, 1, 2, 3, 4, 5};
 
    for (int &i : v) // access by reference (const allowed)
        std::cout << i << ' ';
 
    std::cout << '\n';
 
    for (auto i : v) // compiler uses type inference to determine the right type
        std::cout << i << ' ';
 
    std::cout << '\n';
 
    for (int i : v) // access by value as well
        std::cout << i << ' ';
 
    std::cout << '\n';
}

Output:

0 1 2 3 4 5
0 1 2 3 4 5
0 1 2 3 4 5