# for_each

 Category: algorithms Component type: function

## Prototype

```template <class InputIterator, class UnaryFunction>
UnaryFunction for_each(InputIterator first, InputIterator last, UnaryFunction f);
```

## Description

`For_each` applies the functors `f` to each element in the range `[first, last)`; `f`'s return value, if any, is ignored. Applications are performed in forward order, i.e. from `first` to `last`. `For_each` returns the function object after it has been applied to each element. [1]

## Definition

Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h.

## Requirements on types

• `InputIterator` is a model of InputIterator
• `UnaryFunction` is a model of UnaryFunction
• `UnaryFunction` does not apply any non-constant operation through its argument.
• `InputIterator`'s value type is convertible to `UnaryFunction`'s argument type.

## Preconditions

• `[first, last)` is a valid range.

## Complexity

Linear. Exactly `last - first` applications of `UnaryFunction`.

## Example

```template<class T> struct print : public unary_function<T, void>
{
print(ostream& out) : os(out), count(0) {}
void operator() (T x) { os << x << ' '; ++count; }
ostream& os;
int count;
};

int main()
{
int A[] = {1, 4, 2, 8, 5, 7};
const int N = sizeof(A) / sizeof(int);

print<int> P = for_each(A, A + N, print<int>(cout));
cout << endl << P.count << " objects printed." << endl;
}
```

## Notes

[1] This return value is sometimes useful, since a function object may have local state. It might, for example, count the number of times that it is called, or it might have a status flag to indicate whether or not a call succeeded.

The functors, `count`, `copy`