---
title: mutableBytes
framework: foundation
role: symbol
role_heading: Instance Property
path: foundation/nsmutabledata/mutablebytes
---

# mutableBytes

A pointer to the data contained by the mutable data object.

## Declaration

```swift
var mutableBytes: UnsafeMutableRawPointer { get }
```

## Discussion

Discussion If the length of the receiver’s data is not zero, this property is guaranteed to contain a pointer to the object’s internal bytes. If the length of receiver’s data is zero, this property may or may not contain NULL dependent upon many factors related to how the object was created (moreover, in this case the method result might change between different releases). The returned pointer is valid until the data object is deallocated. note: This property is similar to, but different than the bytes property. The bytes property contains a pointer to a constant. You can use The bytes pointer to read the data managed by the data object, but you cannot modify that data. However, if the mutableBytes property contains a non-null pointer, this pointer points to mutable data. You can use the mutableBytes pointer to modify the data managed by the data object. A sample using this method can be found in Working With Mutable Binary Data.

## See Also

### Related Documentation

- [bytes](foundation/nsdata/bytes.md)