std::count, std::count_if
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| Déclaré dans l'en-tête <algorithm>
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| template< class InputIt, class T > typename iterator_traits<InputIt>::difference_type |
(1) | |
| template< class InputIt, class UnaryPredicate > typename iterator_traits<InputIt>::difference_type |
(2) | |
Retourne le nombre d'éléments dans la gamme
[first, last) satisfaisant des critères spécifiques. La première version compte les éléments qui sont égaux à value, la deuxième version compte les éléments pour lesquels prédicat retourne p true . Original:
Returns the number of elements in the range
[first, last) satisfying specific criteria. The first version counts the elements that are equal to value, the second version counts elements for which predicate p returns true. The text has been machine-translated via Google Translate.
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Sommaire |
[modifier] Paramètres
| first, last | - | l'éventail des éléments à examiner
Original: the range of elements to examine The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
| value | - | la valeur à rechercher
Original: the value to search for The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
| p | - | prédicat unéaire qui retourne true pour les éléments requis . Original: for the required elements The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. L'expression p(v) doit pouvoir être convertie à bool pour tout argument |
| Type requirements | ||
-InputIt must meet the requirements of InputIterator.
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[modifier] Retourne la valeur
certain nombre d'éléments satisfaisant la condition .
Original:
number of elements satisfying the condition.
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[modifier] Complexité
exactement
last - first comparaisons / applications du prédicatOriginal:
exactly
last - first comparisons / applications of the predicateThe text has been machine-translated via Google Translate.
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[modifier] Mise en œuvre possible
| First version |
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template<class InputIt, class T> typename iterator_traits<InputIt>::difference_type count(InputIt first, InputIt last, const T& value) { typename iterator_traits<InputIt>::difference_type ret = 0; for (; first != last; ++first) { if (*first == value) { ret++; } } return ret; } |
| Second version |
template<class InputIt, class UnaryPredicate> typename iterator_traits<InputIt>::difference_type count_if(InputIt first, InputIt last, UnaryPredicate p) { typename iterator_traits<InputIt>::difference_type ret = 0; for (; first != last; ++first) { if (p(*first)) { ret++; } } return ret; } |
[modifier] Exemple
Au code
count utilise pour déterminer le nombre de nombres entiers dans un std::vector correspond à une valeur cible .
Original:
The following code uses
count to determine how many integers in a std::vector match a target value.
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#include <algorithm> #include <iostream> #include <vector> int main() { int data[] = { 1, 2, 3, 4, 4, 3, 7, 8, 9, 10 }; std::vector<int> v(data, data+10); int target1 = 3; int target2 = 5; int num_items1 = std::count(v.begin(), v.end(), target1); int num_items2 = std::count(v.begin(), v.end(), target2); std::cout << "number: " << target1 << " count: " << num_items1 << '\n'; std::cout << "number: " << target2 << " count: " << num_items2 << '\n'; }
Résultat :
number: 3 count: 2 number: 5 count: 0
Cet exemple utilise un expression lambda de compter des éléments divisible par 3 .
Original:
This example uses a expression lambda to count elements divisible by 3.
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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#include <algorithm> #include <iostream> #include <vector> int main() { int data[] = { 1, 2, 3, 4, 4, 3, 7, 8, 9, 10 }; std::vector<int> v(data, data+10); int num_items1 = std::count_if(v.begin(), v.end(), [](int i) {return i % 3 == 0;}); std::cout << "number divisible by three: " << num_items1 << '\n'; }
Résultat :
number divisible by three: 3
