function template
<algorithm>

std::find_if

template <class InputIterator, class UnaryPredicate>
   InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred);
Find element in range
Returns an iterator to the first element in the range [first,last) for which pred returns true. If no such element is found, the function returns last.

The behavior of this function template is equivalent to:
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template<class InputIterator, class UnaryPredicate>
  InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred)
{
  while (first!=last) {
    if (pred(*first)) return first;
    ++first;
  }
  return last;
}


Parameters

first, last
Input iterators to the initial and final positions in a sequence. The range used is [first,last), 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 argument and returns a value convertible to bool. The value returned indicates whether the element is considered a match in the context of this function.
The function shall not modify its argument.
This can either be a function pointer or a function object.

Return value

An iterator to the first element in the range for which pred does not return false.
If pred is false for all elements, the function returns last.

Example

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// find_if example
#include <iostream>     // std::cout
#include <algorithm>    // std::find_if
#include <vector>       // std::vector

bool IsOdd (int i) {
  return ((i%2)==1);
}

int main () {
  std::vector<int> myvector;

  myvector.push_back(10);
  myvector.push_back(25);
  myvector.push_back(40);
  myvector.push_back(55);

  std::vector<int>::iterator it = std::find_if (myvector.begin(), myvector.end(), IsOdd);
  std::cout << "The first odd value is " << *it << '\n';

  return 0;
}


Output:
The first odd value is 25

Complexity

Up to linear in the distance between first and last: Calls pred for each element until a match is found.

Data races

Some (or all) of the objects in the range [first,last) are accessed (once at most).

Exceptions

Throws if either pred or an operation on an iterator throws.
Note that invalid parameters cause undefined behavior.

See also

find
Find value in range (function template )
for_each
Apply function to range (function template )

C++