---
title: "decodeCString(_:as:repairingInvalidCodeUnits:)"
framework: swift
role: symbol
role_heading: Type Method
path: "swift/string/decodecstring(_:as:repairinginvalidcodeunits:)-46n2p"
---

# decodeCString(_:as:repairingInvalidCodeUnits:)

Creates a new string by copying the null-terminated data referenced by the given pointer using the specified encoding.

## Declaration

```swift
static func decodeCString<Encoding>(_ cString: UnsafePointer<Encoding.CodeUnit>?, 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

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

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))"

## See Also

### Converting a C String

- [init(bytes:encoding:)](swift/string/init(bytes:encoding:).md)
- [init(bytesNoCopy:length:encoding:freeWhenDone:)](swift/string/init(bytesnocopy:length:encoding:freewhendone:).md)
- [init(validatingCString:)](swift/string/init(validatingcstring:)-992vo.md)
- [init(validatingCString:)](swift/string/init(validatingcstring:)-98wra.md)
- [init(cString:)](swift/string/init(cstring:)-2p84k.md)
- [init(cString:)](swift/string/init(cstring:)-6kr8s.md)
- [init(cString:encoding:)](swift/string/init(cstring:encoding:)-3h7bc.md)
- [init(cString:encoding:)](swift/string/init(cstring:encoding:)-3qgzd.md)
- [init(decodingCString:as:)](swift/string/init(decodingcstring:as:)-8way7.md)