std::for_each

Defined in header `<algorithm>`
template< class InputIt, class UnaryFunction > UnaryFunction for_each( InputIt first, InputIt last, UnaryFunction f );

Applies the given function object f to the result of dereferencing every iterator in the range [first, last), in order.

If InputIt is a mutable iterator, f may modify the elements of the range through the dereferenced iterator. If f returns a result, the result is ignored.

first, last	-	the range to apply the function to
f	-	function object, to be applied to the result of dereferencing every iterator in the range `[first, last)` The signature of the function should be equivalent to the following: void fun(const Type &a); The signature does not need to have const &. The type Type must be such that an object of type InputIt can be dereferenced and then implicitly converted to Type.
Type requirements
- `InputIt` must meet the requirements of `InputIterator`.
- `UnaryFunction` must meet the requirements of `MoveConstructible`. Does not have to be `CopyConstructible`

[edit] Return value

`f`	(until C++11)
std::move(f)	(since C++11)

[edit] Complexity

Exactly last - first applications of f

[edit] Possible implementation

template<class InputIt, class UnaryFunction>
UnaryFunction for_each(InputIt first, InputIt last, UnaryFunction f)
{
    for (; first != last; ++first) {
        f(*first);
    }
    return f;
}

[edit] Example

The following example uses a lambda function to increment all of the elements of a vector and then uses an overloaded operator() in a functor to compute their sum:

Run this code

#include <vector>
#include <algorithm>
#include <iostream>
 
struct Sum {
    Sum() { sum = 0; }
    void operator()(int n) { sum += n; }
 
    int sum;
};
 
int main()
{
    std::vector<int> nums{3, 4, 2, 9, 15, 267};
 
    std::cout << "before:";
    for (auto n : nums) {
        std::cout << ' ' << n;
    }
    std::cout << '\n';
 
    std::for_each(nums.begin(), nums.end(), [](int &n){ n++; });
 
    // Calls Sum::operator() for each number
    Sum s = std::for_each(nums.begin(), nums.end(), Sum());
 
    std::cout << "after: ";
    for (auto n : nums) {
        std::cout << ' ' << n;
    }
    std::cout << '\n';
    std::cout << "sum: " << s.sum << '\n';
}

Output:

before: 3 4 2 9 15 267
after:  4 5 3 10 16 268
sum: 306

[edit] See also

transform	applies a function to a range of elements (function template)
range-for loop	executes loop over range (since C++11)
for_each (parallelism TS)	similar to std::for_each except returns void (function template)
for_each_n (parallelism TS)	applies a function object to the first n elements of a sequence (function template)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Technical Specifications