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 find_if()
Apache C++ Standard Library Reference Guide

find_if()

Library:  Algorithms

Function

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Summary

Algorithm that finds an occurrence of a value in a sequence that satisfies a specified predicate

Synopsis

#include <algorithm>

namespace std {
template <class InputIterator, class Predicate>
InputIterator find_if(InputIterator start,
InputIterator finish,
Predicate pred);
}

Description

The find_if() algorithm allows you to search for the first element in a sequence that satisfies a particular condition. The sequence is defined by iterators start and finish, while the condition is defined by the third argument: a predicate function that returns a boolean value. find_if() returns the first iterator i in the range [start, finish) for which the following condition holds:

pred(*i) == true.

If no such iterator is found, find_if() returns finish.

Complexity

find_if() performs at most finish-start applications of the corresponding predicate.

Example

//
//  find.cpp
//

#include <vector>      // for vector
#include <algorithm>   // for adjacent_find, find
#include <functional>  // for bind1st, equal_to
#include <iostream>    // for cout, endl

int main ()
{
// Typedef for convenience.
typedef std::vector<int, std::allocator<int> > Vector;

const Vector::value_type arr[] = { 0, 1, 2, 2, 3,
4, 2, 2, 6, 7 };

// Set up a vector.
const Vector v1 (arr, arr + sizeof arr / sizeof *arr);

// Try find.
Vector::const_iterator it = std::find (v1.begin (),
v1.end (), 3);

std::cout << *it << ' ';

// Try find_if.
it = std::find_if (v1.begin (), v1.end (),
std::bind1st (std::equal_to<Vector::value_type>(),
3));

std::cout << *it << ' ';

it = std::adjacent_find (v1.begin (), v1.end ());

std::cout << *it << ' ';

it = std::adjacent_find (v1.begin (), v1.end (),
std::equal_to<Vector::value_type>());

std::cout << *it << std::endl;

return 0;
}

Program Output:

3 3 2 2