# decodeCString(_:as:repairingInvalidCodeUnits:) Creates a new string by copying the null-terminated data referenced by the given pointer using the specified encoding. ``` static func decodeCString(_ cString: UnsafePointer?, as encoding: Encoding.Type, repairingInvalidCodeUnits isRepairing: Bool = true) -> (result: String, repairsMade: Bool)? where Encoding : _UnicodeEncoding ``` ## Parameters `cString` A pointer to a null-terminated sequence of code units encoded in `encoding`. `encoding` The Unicode encoding of the data referenced by `cString`. `isRepairing` Pass `true` to create a new string, even when the data referenced by `cString` contains ill-formed sequences. Ill-formed sequences are replaced with the Unicode replacement character (`"\u{FFFD}"`). Pass `false` to interrupt the creation of the new string if an ill-formed sequence is detected. ## Return Value A tuple with the new string and a Boolean value that indicates whether any repairs were made. If `isRepairing` is `false` and an ill-formed sequence is detected, this method returns `nil`. ## Discussion When you pass `true` as `isRepairing`, this method replaces ill-formed sequences with the Unicode replacement character (`"\u{FFFD}"`); otherwise, an ill-formed sequence causes this method to stop decoding and return `nil`. The following example calls this method with pointers to the contents of two different `CChar` arrays—the first with well-formed UTF-8 code unit sequences and the second with an ill-formed sequence at the end. ``` let validUTF8: [UInt8] = [67, 97, 102, 195, 169, 0] validUTF8.withUnsafeBufferPointer { ptr in let s = String.decodeCString(ptr.baseAddress, as: UTF8.self, repairingInvalidCodeUnits: true) print(s) } // Prints "Optional((result: "Café", repairsMade: false))" let invalidUTF8: [UInt8] = [67, 97, 102, 195, 0] invalidUTF8.withUnsafeBufferPointer { ptr in let s = String.decodeCString(ptr.baseAddress, as: UTF8.self, repairingInvalidCodeUnits: true) print(s) } // Prints "Optional((result: "Caf�", repairsMade: true))" ``` --- 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)