std::count, std::count_if — cppreference.com
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    std::count, std::count_if

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    C++
     
    Bibliothèque d'algorithmes
    Fonctions
    Original:
    Functions
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    Non-modification de la séquence des opérations
    Original:
    Non-modifying sequence operations
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    Modification de la séquence des opérations
    Original:
    Modifying sequence operations
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    Des opérations de partitionnement
    Original:
    Partitioning operations
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    Opérations de tri (sur les gammes triés)
    Original:
    Sorting operations (on sorted ranges)
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    is_sorted (C++11)
    is_sorted_until (C++11)
    sort
    Opérations binaires de recherche (sur les gammes triés)
    Original:
    Binary search operations (on sorted ranges)
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    Définir les opérations (sur les gammes triés)
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    Set operations (on sorted ranges)
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    Opérations Heap
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    Heap operations
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    Minimum / maximum de fonctionnement
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    Minimum/maximum operations
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    Opérations numériques
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    Numeric operations
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    Bibliothèque C
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    C library
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    <tbody> </tbody>
    Déclaré dans l'en-tête <algorithm>
    template< class InputIt, class T > typename iterator_traits<InputIt>::difference_type count( InputIt first, InputIt last, const T &value );
    		 (1)
    template< class InputIt, class UnaryPredicate > typename iterator_traits<InputIt>::difference_type count_if( InputIt first, InputIt last, UnaryPredicate p );
    		 (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.
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    Paramètres

    first, last -
    l'éventail des éléments à examiner
    Original:
    the range of elements to examine
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    value -
    la valeur à rechercher
    Original:
    the value to search for
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    p - prédicat unéaire qui retourne ​true
    pour les éléments requis
    Original:
    for the required elements
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    .

    L'expression p(v) doit pouvoir être convertie à bool pour tout argument v de type (possiblement const) VT, où VT est le type de valeur de InputIt, inconditionellement de value category, et ne doit pas modifier v. Ainsi, un type-paramètre VT&n'est pas permis ainsi que pour VT sauf pour VT un déplacement est équivalent à une copie (depuis C++11). ​

    Type requirements
    -
    InputIt must meet the requirements of InputIterator.

    Retourne la valeur

    certain nombre d'éléments satisfaisant la condition .
    Original:
    number of elements satisfying the condition.
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    Complexité

    exactement last - first comparaisons / applications du prédicat
    Original:
    exactly last - first comparisons / applications of the predicate
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    Mise en œuvre possible

    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.
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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