std::unordered_map::operator[]

 

C++

Linguaggio

Concetti

Libreria di Utilità

Stringhe

Contenitori

Algoritmi

Iteratori

Libreria matematca

Input/output

Localizzazione

Espressioni regolari(C++11)

Operazioni atomicche(C++11)

Multithreading(C++11)

 

Contenitori libreria

array (C++11)

vector

deque

forward_list (C++11)

list

set

multiset

map

multimap

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

stack

queue

priority_queue

 

std::unordered_map

Membri funzioni Original: Member functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

unordered_map::unordered_map

unordered_map::~unordered_map

unordered_map::operator=

unordered_map::get_allocator

Iteratori Original: Iterators The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

unordered_map::begin unordered_map::cbegin

unordered_map::end unordered_map::cend

Capacità Original: Capacity The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

unordered_map::erase

unordered_map::size

unordered_map::max_size

Modificatori Original: Modifiers The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

unordered_map::clear

unordered_map::insert

unordered_map::emplace

unordered_map::emplace_hint

unordered_map::erase

unordered_map::swap

Lookup Original: Lookup The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

unordered_map::count

unordered_map::find

unordered_map::equal_range

Benna interfaccia Original: Bucket interface The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

unordered_map::begin2

unordered_map::end2

unordered_map::bucket_count

unordered_map::max_bucket_count

unordered_map::bucket_size

unordered_map::bucket

Politica di Hash Original: Hash policy The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

unordered_map::load_factor

unordered_map::max_load_factor

unordered_map::rehash

unordered_map::reserve

Osservatori Original: Observers The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

unordered_map::hash_function

unordered_map::key_eq

 

T& operator[](const Key& key );	(1)	(dal C++11)
T& operator[]( Key&& key );	(2)	(dal C++11)

Inserisce un nuovo elemento al contenitore con key come chiave e predefinito al valore costruito mappato e restituisce un riferimento al valore di nuova costruzione mappati. Se un elemento con key chiave esiste già, non viene eseguita e l'inserimento di un riferimento al suo valore mappato viene restituito.

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)

Esegue sostanza (insert(std::make_pair(key, T())).first)->second.

Original:

Essentially performs (insert(std::make_pair(key, T())).first)->second.

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2)

Esegue sostanza (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().

Parametri

key

-

la chiave dell'elemento da trovare 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.

Valore di ritorno

Riferimento al valore mappato del nuovo elemento se nessun elemento con chiave key esistito. Altrimenti un riferimento al valore mappato dell'elemento esistente viene restituito.

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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Complessità

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

Vedi anche

at	accedere elemento specificato con verifica dei limiti 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. (metodo pubblico)

Esempio

Conta le occorrenze di ogni parola in un vettore di stringhe .

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'