# CFURLCreateAbsoluteURLWithBytes(_:_:_:_:_:_:) Creates a new `CFURL` object by resolving the relative portion of a URL, specified as bytes, against its given base URL. ``` func CFURLCreateAbsoluteURLWithBytes(_ alloc: CFAllocator!, _ relativeURLBytes: UnsafePointer!, _ length: CFIndex, _ encoding: CFStringEncoding, _ baseURL: CFURL!, _ useCompatibilityMode: Bool) -> CFURL! ``` ## Parameters `alloc` The allocator to use to allocate memory for the new `CFURL` object. Pass `NULL` or [`kCFAllocatorDefault`](/documentation/CoreFoundation/kCFAllocatorDefault) to use the current default allocator. `relativeURLBytes` The character bytes that represent a relative URL to convert into a `CFURL` object. `length` The number of bytes in `relativeURLBytes`. `encoding` The string encoding of the `relativeURLBytes` string. This encoding is also used to interpret percent escape sequences. `baseURL` The URL to which `relativeURLBytes` is relative. `useCompatibilityMode` If `true`, the rules historically used on the web are used to resolve the string specified by the `relativeURLBytes` parameter against `baseURL`. These rules are generally listed in the RFC as optional or alternate interpretations. Otherwise, the strict rules from the RFC are used. ## Return Value A new `CFURL` object, or `NULL` if `relativeURLBytes` cannot be made absolute. Ownership follows the create rule. See [The Create Rule](https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFMemoryMgmt/Concepts/Ownership.html#//apple_ref/doc/uid/20001148-103029). ## Discussion This function interprets the provided bytes using the specified string encoding to create the relative portion of the URL’s address. > Note: > This function does not support string encoding which isn’t a superset of ASCII encoding. Both ``doc://com.apple.corefoundation/documentation/CoreFoundation/CFURLGetBytes(_:_:_:)`` and ``doc://com.apple.corefoundation/documentation/CoreFoundation/CFURLGetByteRangeForComponent(_:_:_:)`` require 7-bit ASCII characters to be stored in a single 8-bit byte. The following ``doc://com.apple.corefoundation/documentation/CoreFoundation/CFStringEncodings`` can be used: ``doc://com.apple.corefoundation/documentation/CoreFoundation/CFStringBuiltInEncodings/macRoman``, ``doc://com.apple.corefoundation/documentation/CoreFoundation/CFStringBuiltInEncodings/windowsLatin1``, ``doc://com.apple.corefoundation/documentation/CoreFoundation/CFStringBuiltInEncodings/isoLatin1``, ``doc://com.apple.corefoundation/documentation/CoreFoundation/CFStringBuiltInEncodings/nextStepLatin``, ``doc://com.apple.corefoundation/documentation/CoreFoundation/CFStringBuiltInEncodings/ASCII`` and ``doc://com.apple.corefoundation/documentation/CoreFoundation/CFStringBuiltInEncodings/UTF8``. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)