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# std::for_each

From cppreference.com
< cpp‎ | algorithm

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.

### [edit] Parameters

first, last | - | the range to apply the function to
f | - | the unary function object to be applied
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) [edit]
range-for loop | executes loop over range (since C++11) [edit]

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