# write(_:maxLength:) Writes the contents of a provided data buffer to the receiver. ``` func write(_ buffer: UnsafePointer, maxLength len: Int) -> Int ``` ## Parameters `buffer` The data to write. `len` The length of the data buffer, in bytes. > Important: > The behavior of this method is undefined if you pass a negative or zero number. ## Return Value A number indicating the outcome of the operation: - A positive number indicates the number of bytes written. - `0` indicates that a fixed-length stream and has reached its capacity. - `-1` means that the operation failed; more information about the error can be obtained with [`streamError`](/documentation/Foundation/Stream/streamError). ## Discussion --- 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)