---
title: withSubRange
framework: kernel
role: pseudoSymbol
path: kernel/iosubmemorydescriptor/1810054-withsubrange
---

# withSubRange

Create an IOMemoryDescriptor to describe a subrange of an existing descriptor.

## Declaration

```occ
static IOSubMemoryDescriptor * withSubRange(
 IOMemoryDescriptor *of, 
 IOByteCountoffset, 
 IOByteCountlength, 
 IOOptionBitsoptions); 
```

## Parameters

- `of`: The parent IOMemoryDescriptor of which a subrange is to be used for the new descriptor, which will be retained by the subrange IOMemoryDescriptor.
- `offset`: A byte offset into the parent memory descriptor's memory.
- `length`: The length of the subrange.
- `options`: kIOMemoryDirectionMask (options:direction) This nibble indicates the I/O direction to be associated with the descriptor, which may affect the operation of the prepare and complete methods on some architectures.

## Return Value

Return Value The created IOMemoryDescriptor on success, to be released by the caller, or zero on failure.

## Overview

Overview This method creates and initializes an IOMemoryDescriptor for memory consisting of a subrange of the specified memory descriptor. The parent memory descriptor is retained by the new descriptor.