# copyBytes(to:from:) Copies the bytes in a range from the data into a buffer. ``` func copyBytes(to buffer: UnsafeMutableBufferPointer, from range: Range? = nil) -> Int ``` ## Parameters `buffer` A buffer to copy the data into. `range` A range in the data to copy into the buffer. If the range is empty, this function will return 0 without copying anything. If the range is nil, as much data as will fit into `buffer` is copied. ## Return Value Number of bytes copied into the destination buffer. ## Discussion If the count of the range is greater than `MemoryLayout.stride * buffer.count` then only the first `N` bytes will be copied into the buffer.Precondition: The range must be within the bounds of the data. Otherwise `fatalError` is called. --- 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)