std::unordered_map::operator[]
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<tbody> </tbody> T& operator[]( const Key& key ); |
(1) | (depuis C++11) |
T& operator[]( Key&& key ); |
(2) | (depuis C++11) |
key comme la cl par dfaut et la valeur construite mapp et renvoie une rfrence la valeur nouvellement construit mapp. Si un lment de key cl existe dj, aucune insertion est effectue et une rfrence sa valeur mappe est retourn .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.You can help to correct and verify the translation. Click here for instructions.
1)
(insert(std::make_pair(key, T())).first)->second .(insert(std::make_pair(key, T())).first)->second.You can help to correct and verify the translation. Click here for instructions.
2)
(insert(std::make_pair(std::move(key), T())).first)->second .(insert(std::make_pair(std::move(key), T())).first)->second.You can help to correct and verify the translation. Click here for instructions.
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().
Paramtres
| key | - | la cl de l'lment trouver
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. |
Retourne la valeur
key exist. Sinon une rfrence la valeur associe de l'lment actuel est retourn .key existed. Otherwise a reference to the mapped value of the existing element is returned.You can help to correct and verify the translation. Click here for instructions.
Complexit
Average case: constant, worst case: linear in size.
Exemple
| This section is incomplete Reason: no example |
Voir aussi
| accde l'lment spcifi avec vrification de bornes (fonction membre publique) | |
Exemple
Compte les occurrences de chaque mot dans un vecteur de chanes .
Counts the occurrences of each word in a vector of strings.
You can help to correct and verify the translation. Click here for instructions.
#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";
}
}
Rsultat :
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'