# fill

 Category: algorithms Component type: function

### Prototype

```template <class ForwardIterator, class T>
void fill(ForwardIterator first, ForwardIterator last, const T& value);
```

### Description

Fill assigns the value value to every element in the range [first, last). That is, for every iterator i in [first, last), it performs the assignment *i = value.

### Definition

Declared in algo.h. The implementation is in algobase.h.

### Preconditions

• [first, last) is a valid range.

### Complexity

Linear. Fill performs exactly last - first assignments.

### Example

```vector<double> V(4);
fill(V.begin(), V.end(), 137);
assert(V[0] == 137 && V[1] == 137 && V[2] == 137 && V[3] == 137);
```

### Notes

[1] The reason that fill requires its argument to be a mutable forward iterator, rather than merely an output iterator, is that it uses a range [first, last) of iterators. There is no sensible way to describe a range of output iterators, because it is impossible to compare two output iterators for equality. The fill_n algorithm does have an interface that permits use of an output iterator.