std::count, std::count_if
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<tbody> </tbody>| Dclar dans l'en-tte <algorithm>
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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'lments dans la gamme
[first, last) satisfaisant des critres spcifiques. La premire version compte les lments qui sont gaux value, la deuxime version compte les lments pour lesquels prdicat 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.
You can help to correct and verify the translation. Click here for instructions.
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Paramtres
| first, last | - | l'ventail des lments 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 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 | - | prdicat unaire qui retourne true pour les lments 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 |
| Type requirements | ||
-InputIt must meet the requirements of InputIterator.
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Retourne la valeur
certain nombre d'lments satisfaisant la condition .
Original:
number of elements satisfying the condition.
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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Complexit
exactement
last - first comparaisons / applications du prdicatOriginal:
exactly
last - first comparisons / applications of the predicateThe text has been machine-translated via Google Translate.
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Mise en uvre possible
| First version |
|---|
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;
}
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| 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;
}
|
Exemple
Au code
count utilise pour dterminer le nombre de nombres entiers dans un std::vector correspond une valeur cible .
Original:
The following code uses
count to determine how many integers in a std::vector match a target value.
The text has been machine-translated via Google Translate.
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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';
}
Rsultat :
number: 3 count: 2
number: 5 count: 0
Cet exemple utilise un expression lambda de compter des lments 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.
You can help to correct and verify the translation. Click here for instructions.
#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';
}
Rsultat :
number divisible by three: 3