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

From Cppreference

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)	(C++11 feature)

Finds the first element in the range [first, last) satisfying specific criteria. The first version searches for element, equal to value, the second version searches for element for which predicate p returns true, the third version searches for element for which predicate q returns false.

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

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

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

[edit] Example

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

#include <algorithm>
#include <vector>
 
int main()
{
    int n1 = 3;
    int n2 = 5;
 
    std::vector<int> v{0, 1, 2, 3, 4};
 
    std::vector<int>::iterator result1, result2;
 
    result1 = std::find(v.begin(), v.end(), n1);
    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";
    }
}