std::find, std::find_if, std::find_if_not

Elemento definito nell'header `<algorithm>`

`template< class InputIt, class T > InputIt find( InputIt first, InputIt last, const T& value );`	(1)

`template< class InputIt, class UnaryPredicate > InputIt find_if( InputIt first, InputIt last, UnaryPredicate p );`	(2)

`template< class InputIt, class UnaryPredicate > InputIt find_if_not( InputIt first, InputIt last, UnaryPredicate q );`	(3)	(dal C++11)

Queste funzioni trovare il primo elemento nella [first, last) gamma che soddisfa criteri specifici:

1. find ricerche di un elemento pari a value

2. find_if cerca un elemento per il quale predicato p ritorna true

3. find_if_not cerca elemento per il quale predicato q ritorna false

Parametri

first, last	-	la gamma di elementi da esaminare 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	-	valore per confrontare gli elementi Original: value to compare the elements to The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
p	-	unary predicate which returns `true` per l'elemento richiesto Original: for the required element The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. . The signature of the predicate function should be equivalent to the following: `bool pred(const Type &a);` The signature does not need to have `const &`, but the function must not modify the objects passed to it. The type `Type` must be such that an object of type `InputIt` can be dereferenced and then implicitly converted to `Type`.
q	-	unary predicate which returns `false` per l'elemento richiesto Original: for the required element The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. . The signature of the predicate function should be equivalent to the following: `bool pred(const Type &a);` The signature does not need to have `const &`, but the function must not modify the objects passed to it. The type `Type` must be such that an object of type `InputIt` can be dereferenced and then implicitly converted to `Type`.
Type requirements
- `InputIt` must meet the requirements of `InputIterator`.

Valore di ritorno

Iteratore al primo elemento che soddisfa la condizione o last se tale elemento non viene trovato.

Complessità

Al massimo last - first applicazioni del predicato

Possibile implementazione

First version
template<class InputIt, class T> InputIt find(InputIt first, InputIt last, const T& value) { for (; first != last; ++first) { if (*first == value) { return first; } } return last; }
Second version
template<class InputIt, class UnaryPredicate> InputIt find_if(InputIt first, InputIt last, UnaryPredicate p) { for (; first != last; ++first) { if (p(*first)) { return first; } } return last; }
Third version
template<class InputIt, class UnaryPredicate> InputIt find_if_not(InputIt first, InputIt last, UnaryPredicate q) { for (; first != last; ++first) { if (!q(*first)) { return first; } } return last; }

Se non si dispone di C + +11, l'equivalente di std::find_if_not è quello di utilizzare std::find_if con il predicato negato.

template<class InputIt, class UnaryPredicate>
InputIt find_if_not(InputIt first, InputIt last, UnaryPredicate q)
{
    return std::find_if(first, last, std::not1(q));
}

Esempio

Nell'esempio seguente vengono individuati un numero intero in un vettore di interi .

#include <iostream>
#include <algorithm>
#include <vector>

int main()
{
    int n1 = 3;
    int n2 = 5;
 
    std::vector<int> v{0, 1, 2, 3, 4};
 
    auto result1 = std::find(v.begin(), v.end(), n1);
    auto result2 = std::find(v.begin(), v.end(), n2);
 
    if (result1 != v.end()) {
        std::cout << "v contains: " << n1 << '\n';
    } else {
        std::cout << "v does not contain: " << n1 << '\n';
    }

    if (result2 != v.end()) {
        std::cout << "v contains: " << n2 << '\n';
    } else {
        std::cout << "v does not contain: " << n2 << '\n';
    }
}

Output:

v contains: 3
v does not contain: 5

Vedi anche

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)

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