---
title: "CFDataGetMutableBytePtr(_:)"
framework: corefoundation
role: symbol
role_heading: Function
path: "corefoundation/cfdatagetmutablebyteptr(_:)"
---

# CFDataGetMutableBytePtr(_:)

Returns a pointer to a mutable byte buffer of a CFMutableData object.

## Declaration

```swift
func CFDataGetMutableBytePtr(_ theData: CFMutableData!) -> UnsafeMutablePointer<UInt8>!
```

## Parameters

- `theData`: A CFMutableData object. If you pass an immutable CFData object, the behavior is not defined.

## Return Value

Return Value A pointer to the bytes associated with theData.

## Discussion

Discussion If the length of theData‘s data is not zero, this function is guaranteed to return a pointer to a CFMutableData object’s internal bytes. If the length of theData’s data is zero, this function may or may not return NULL dependent upon many factors related to how the object was created (moreover, in this case the function result might change between different releases and on different platforms).