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Showing content from https://cplusplus.com/reference/algorithm/find_if/ below:

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)

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