std::find_if , std::find_if_not in C++

std :: find_if and std :: find_if_not are algorithm functions in C++ Standard Library in <algorithm> header file. These functions provide an efficient way to search for an element in a container using a predicate function.

std :: find_if

This function returns an iterator to the first element in the range [first, last) for which pred(Unary Function) returns true. If no such element is found, the function returns last.

Syntax

InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred);

Parameters

• first, last: range which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
• pred: Unary function that accepts an element in the range as an argument and returns a value in boolean.

Return Value

• This function returns an iterator to the first element in the range [first, last) for which pred(function) returns true. If no such element is found, the function returns last.

Example

The following C++ program illustrates the use of the find_if() function.

// CPP program to illustrate std::find_if #include <bits/stdc++.h> using namespace std; // Returns true if argument is odd bool IsOdd(int i) { return i % 2; } // Driver code int main() {  vector<int> vec{ 10, 25, 40, 55 };  // Iterator to store the position of element found  vector<int>::iterator it;  // std::find_if  it = find_if(vec.begin(), vec.end(), IsOdd);  cout << "The first odd value is " << *it << '\n';  return 0; } 

The first odd value is 25

std :: find_if_not

This function returns an iterator to the first element in the range [first, last) for which pred(Unary Function) returns false. If no such element is found, the function returns last.

Syntax

InputIterator find_if_not (InputIterator first, InputIterator last, UnaryPredicate pred);

Parameters

• first, last: range which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
• pred: Unary function that accepts an element in the range as an argument and returns a value in boolean.

Return value

• This function returns an iterator to the first element in the range [first, last) for which pred(function) returns false.

Example

The following C++ program illustrates the use of the find_if_not() function.

// CPP program to illustrate std::find_if_not #include <bits/stdc++.h> using namespace std; // Returns true if argument is odd bool IsOdd(int i) { return i % 2; } // Driver code int main() {  vector<int> vec{ 10, 25, 40, 55 };  // Iterator to store the position of element found  vector<int>::iterator it;  // std::find_if_not  it = find_if_not(vec.begin(), vec.end(), IsOdd);  cout << "The first non-odd(or even) value is " << *it  << '\n';  return 0; } 

The first non-odd(or even) value is 10

Related Articles: 

• std::search
• std::find
• std::nth_element
• std::find_end