# std::fill

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< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
| (1) |
template< class ForwardIt, class T > void fill( ForwardIt first, ForwardIt last, const T& value ); |  | (until C++20)
template< class ForwardIt, class T > constexpr void fill( ForwardIt first, ForwardIt last, const T& value ); |  | (since C++20)
template< class ExecutionPolicy, class ForwardIt, class T > void fill( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, const T& value ); | (2) | (since C++17)

1) Assigns the given `value` to the elements in the range `[first, last)`.
2) Same as (1), but executed according to `policy`. This overload does not participate in overload resolution unless std::is_execution_policy_v < std::decay_t <ExecutionPolicy>> is true

### Parameters

first, last | - | the range of elements to modify
value | - | the value to be assigned
policy | - | the execution policy to use. See execution policy for details.
Type requirements
- `ForwardIt` must meet the requirements of LegacyForwardIterator.

### Return value

(none)

### Complexity

Exactly `last - first` assignments.

### Exceptions

The overload with a template parameter named `ExecutionPolicy` reports errors as follows:

- If execution of a function invoked as part of the algorithm throws an exception and `ExecutionPolicy` is one of the standard policies, std::terminate is called. For any other `ExecutionPolicy`, the behavior is implementation-defined.
- If the algorithm fails to allocate memory, std::bad_alloc is thrown.

### Possible implementation

    template< class ForwardIt, class T >
    void fill(ForwardIt first, ForwardIt last, const T& value)
    {
        for (; first != last; ++first) {
            *first = value;
        }
    }

### Example

The following code uses `fill()` to set all of the elements of a vector of integers to -1:

Run this code

    #include <algorithm>
    #include <vector>
    #include <iostream>

    int main()
    {
        std::vector<int> v{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};

        std::fill(v.begin(), v.end(), -1);

        for (auto elem : v) {
            std::cout << elem << " ";
        }
        std::cout << "\n";
    }

Output:

    -1 -1 -1 -1 -1 -1 -1 -1 -1 -1

### See also

fill_n | copy-assigns the given value to N elements in a range (function template)
copycopy_if (C++11) | copies a range of elements to a new location (function template)
generate | assigns the results of successive function calls to every element in a range (function template)
transform | applies a function to a range of elements (function template)

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