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std::unordered_map::operator[]

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std::unordered_map
Member-Funktionen
Original:
Member functions
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unordered_map::unordered_map
unordered_map::~unordered_map
unordered_map::operator=
unordered_map::get_allocator
Iteratoren
Original:
Iterators
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unordered_map::begin
unordered_map::cbegin
unordered_map::end
unordered_map::cend
Kapazität
Original:
Capacity
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unordered_map::erase
unordered_map::size
unordered_map::max_size
Modifiers
Original:
Modifiers
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unordered_map::clear
unordered_map::insert
unordered_map::emplace
unordered_map::emplace_hint
unordered_map::erase
unordered_map::swap
Lookup
Original:
Lookup
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unordered_map::count
unordered_map::find
unordered_map::equal_range
Eimer Schnittstelle
Original:
Bucket interface
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unordered_map::begin2
unordered_map::end2
unordered_map::bucket_count
unordered_map::max_bucket_count
unordered_map::bucket_size
unordered_map::bucket
Hash Politik
Original:
Hash policy
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unordered_map::load_factor
unordered_map::max_load_factor
unordered_map::rehash
unordered_map::reserve
Beobachter
Original:
Observers
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unordered_map::hash_function
unordered_map::key_eq
 
T& operator[]( const Key& key );
(1) (seit C++11)
T& operator[]( Key&& key );
(2) (seit C++11)
Fügt ein neues Element in den Behälter mit key als Schlüssel und Standard gebaut mapped Wert und gibt einen Verweis auf das neu errichtete kartiert Wert. Wenn ein Element mit Schlüssel key bereits existiert, wird keine Insertion durchgeführt und ein Verweis auf seine kartiert Wert zurückgegeben .
Original:
Inserts a new element to the container using key as the key and default constructed mapped value and returns a reference to the newly constructed mapped value. If an element with key key already exists, no insertion is performed and a reference to its mapped value is returned.
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1)
Führt im wesentlichen (insert(std::make_pair(key, T())).first)->second .
Original:
Essentially performs (insert(std::make_pair(key, T())).first)->second.
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2)
Führt im wesentlichen (insert(std::make_pair(std::move(key), T())).first)->second .
Original:
Essentially performs (insert(std::make_pair(std::move(key), T())).first)->second.
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If an insertion occurs and results in a rehashing of the container, all iterators are invalidated. Otherwise iterators are not affected. References are not invalidated. Rehashing occurs only if the new number of elements is higher than max_load_factor()*bucket_count().

Inhaltsverzeichnis

[Bearbeiten] Parameter

key -
der Schlüssel des Elements zu finden
Original:
the key of the element to find
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[Bearbeiten] Rückgabewert

Bezugnahme auf den zugeordneten Wert des neuen Elements, wenn kein Element mit Schlüssel key existierte. Andernfalls wird ein Verweis auf das zugeordnete Wert der bestehenden Element zurückgegeben .
Original:
Reference to the mapped value of the new element if no element with key key existed. Otherwise a reference to the mapped value of the existing element is returned.
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[Bearbeiten] Komplexität

Average case: constant, worst case: linear in size.

[Bearbeiten] Beispiel

[Bearbeiten] Siehe auch

Zugriff auf angegebene Element mit Überprüfung von Grenzen
Original:
access specified element with bounds checking
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(öffentliche Elementfunktion) [edit]

[Bearbeiten] Beispiel

Zählt die Vorkommen jedes Wort in einem Vektor von Strings .

Original:

Counts the occurrences of each word in a vector of strings.

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#include <string>
#include <iostream>
#include <vector>
#include <unordered_map>
 
int main()
{
    std::vector<std::string> words = { 
        "this", "sentence", "is", "not", "a", "sentence",
	"this", "sentence", "is", "a", "hoax" 
    };
 
    std::unordered_map<std::string,size_t>  word_map;
    for (auto w : words) {
        ++word_map[w];
    }
 
    for (auto elem : word_map) {
        std::cout << elem.second
	          << " occurrences of word '"
	          << elem.first << "'\n";
    }
}

Output:

1 occurrences of word 'hoax'
2 occurrences of word 'this'
2 occurrences of word 'a'
2 occurrences of word 'is'
1 occurrences of word 'not'
3 occurrences of word 'sentence'