Converting a C char array to a String

The C array char name[8] is imported to Swift as a tuple:

(Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8)

The address of name is the same as the address of name[0], andSwift preserves the memory layout of structures imported from C, asconfirmed by Apple engineer Joe Groff:

... You can leave the struct defined in C and import it into Swift. Swift will respect C's layout.

As a consequence, we can pass the address of record.name,converted to an UInt8 pointer, tothe String initializer. The following code has been updated for Swift 4.2 and later:

let record = someFunctionReturningAStructRecord()let name = withUnsafePointer(to: record.name) {    $0.withMemoryRebound(to: UInt8.self, capacity: MemoryLayout.size(ofValue: $0)) {        String(cString: $0)    }}

NOTE: It is assumed that the bytes in name[] are a valid NUL-terminated UTF-8 sequence.

For older versions of Swift:

// Swift 2:var record = someFunctionReturningAStructRecord()let name = withUnsafePointer(&record.name) {    String.fromCString(UnsafePointer($0))!}// Swift 3:var record = someFunctionReturningAStructRecord()let name = withUnsafePointer(to: &record.name) {    $0.withMemoryRebound(to: UInt8.self, capacity: MemoryLayout.size(ofValue: record.name)) {        String(cString: $0)    }}

You can actually collect a tuple into an array by using Swift's variadic parameter syntax:

let record = getRecord()let (int8s: Int8...) = myRecord          // int8s is an [Int8]let uint8s = int8s.map { UInt8($0) }let string = String(bytes: uint8s, encoding: NSASCIIStringEncoding)// myString == Optional("12345678")

I'm interested in working this out for my own purposes as well, so I added a new function:

func asciiCArrayToSwiftString(cString:Int8...) -> String{    var swiftString = String()            // The Swift String to be Returned is Intialized to an Empty String    var workingCharacter:UnicodeScalar = UnicodeScalar(UInt8(cString[0]))    var count:Int = cString.count    for var i:Int = 0; i < count; i++    {        workingCharacter = UnicodeScalar(UInt8(cString[i])) // Convert the Int8 Character to a Unicode Scalar        swiftString.append(workingCharacter)             // Append the Unicode Scalar    }    return swiftString                     // Return the Swift String}

I call this function with:

    let t:Int8 = Int8(116)    let e:Int8 = Int8(101)    let s:Int8 = Int8(115)    let testCString = (t, e, s, t)    let testSwiftString = wispStringConverter.asciiCArrayToSwiftString(testCString.0, testCString.1, testCString.2, testCString.3)    println("testSwiftString = \(testSwiftString)")

the resulting output is:

testSwiftString = test