std::unordered_map::operator[]
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<metanoindex/>
<tbody> </tbody> 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.The text has been machine-translated via Google Translate.
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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.The text has been machine-translated via Google Translate.
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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.The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
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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().
Parameter
| key | - | der Schlüssel des Elements zu finden
Original: the key of the element to find The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
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.The text has been machine-translated via Google Translate.
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Komplexität
Average case: constant, worst case: linear in size.
Beispiel
| This section is incomplete Reason: no example |
Siehe auch
Zugriff auf angegebene Element mit Überprüfung von Grenzen Original: access specified element with bounds checking The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (öffentliche Elementfunktion) | |
Beispiel
Zählt die Vorkommen jedes Wort in einem Vektor von Strings .
Original:
Counts the occurrences of each word in a vector of strings.
The text has been machine-translated via Google Translate.
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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'