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# CFBitVectorCreateMutableCopy(_:_:_:)

Creates a new mutable bit vector from a pre-existing bit vector.

```
func CFBitVectorCreateMutableCopy(_ allocator: CFAllocator!, _ capacity: CFIndex, _ bv: CFBitVector!) -> CFMutableBitVector!
```

## Parameters

`allocator`

The allocator to use to allocate memory for the new object. Pass `NULL` or kCFAllocatorDefault to use the current default allocator.

`capacity`

The maximum number of values that can be contained by the new bit vector. The bit vector starts with the same number of values as `bv` and can grow to this number of values (it can have less).

    Pass     `0`     to specify that the maximum capacity is not limited. If non-    `0`    ,     `capacity`     must be large enough to hold all bit values from     `bv`    .

`bv`

The bit vector to copy.

## Return Value

A new bit vector holding the same bit values as `bv`. Ownership follows the [The Create Rule](https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFMemoryMgmt/Concepts/Ownership.html#//apple_ref/doc/uid/20001148-103029)

## See Also

[`CFBitVectorSetCount(_:_:)`](/documentation/CoreFoundation/CFBitVectorSetCount(_:_:))

Changes the size of a mutable bit vector.


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