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.
C++
// 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.
C++
// 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
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