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

From cppreference.com
 
 
 
Defined in header <algorithm>
template< class InputIterator, class T >

InputIterator find( InputIterator first, InputIterator last,

                    const T& value );
(1)
template< class InputIterator, class UnaryPredicate >

InputIterator find_if( InputIterator first, InputIterator last,

                       UnaryPredicate p );
(2)
template< class InputIterator, class UnaryPredicate >

InputIterator find_if_not( InputIterator first, InputIterator last,

                           UnaryPredicate q );
(3) (since C++11)

These functions find the first element in the range [first, last) that satisfies specific criteria:

1. find searches for an element equal to value

2. find_if searches for an element for which predicate p returns true

3. find_if_not searches for element for which predicate q returns false

Contents

[edit] Parameters

first, last - the range of elements to examine
value - value to compare the elements to
p - unary predicate which returns ​true for the required element.

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 InputIterator can be dereferenced and then implicitly converted to Type. ​

q - unary predicate which returns ​false for the required element.

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 InputIterator can be dereferenced and then implicitly converted to Type. ​

[edit] Return value

iterator to the first element satisfying the condition or last if no such element is found.

[edit] Complexity

At most last - first applications of the predicate

[edit] Possible implementation

If you do not have C++11, an equivalent to std::find_if_not is to use std::find_if with the negated predicate.

[edit] Example

The following example finds an integer in a vector of integers.

#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

[edit] See also

finds two identical (or some other relationship) items adjacent to each other
(function template) [edit]
finds the last sequence of elements in a certain range
(function template) [edit]
searches for any one of a set of elements
(function template) [edit]
finds the first position where two ranges differ
(function template) [edit]
searches for a range of elements
(function template) [edit]