I am interfacing with libxml2 in swift, and the C APIs binding (still) produce UnsafePointer<Int8>! for c-strings. Whereas Swift APIs normally result in UnsafePointer<UInt8>!.
So my question is - am I doing the string to null-terminated C-string in a proper way?
let cfilePath = unsafeBitCast(myStringString.nulTerminatedUTF8.withUnsafeBufferPointer { $0.baseAddress }, to: UnsafePointer<Int8>.self)
Should I instead prefer using some other method instead of just bypassing Swift type checking with interpreting UInt8 bytes as Int8 bytes?
I'm not sure this solves your problem exactly but for a project where I am sending strings over bluetooth this did the trick:
extension String {
var nullTerminated: Data? {
if var data = self.data(using: String.Encoding.utf8) {
data.append(0)
return data
}
return nil
}
}
Use like this
let data = "asfasf".nullTerminated
I can't find the function the other answers are referencing: nulTerminatedUTF8. Maybe it already does this.
don't use unsafeBitCast for that!!
let cstr = "alpha".nulTerminatedUTF8
let int8arr = cstr.map{ Int8(bitPattern: $0) }
let uint8arr = Array(cstr)
print(int8arr.dynamicType, uint8arr.dynamicType)
// Array<Int8> Array<UInt8>
update
let uint8: UInt8 = 200
let int8 = Int8(bitPattern: uint8)
print(uint8, int8)
// 200 -56
Related
there. I am a beginner in Swift and am trying to convert an older program to Swift3. I´ve managed to fix a bunch of errors, but I cannot get this function to work.
fileprivate func extractEntitlements(_ entitlementData: Data) -> NSDictionary? {
var originalEntitlementsData = entitlementData
let xmlStart = "<?xml".data(using: String.Encoding.ascii, allowLossyConversion: true)
let bytes = (originalEntitlementsData as NSData).bytes
for i in 0...(originalEntitlementsData.count - xmlStart!.count) {
if memcmp((xmlStart! as NSData).bytes, bytes + i, Int(xmlStart!.count)) == 0 {
let end = originalEntitlementsData.count - i
**originalEntitlementsData = originalEntitlementsData.subdata(in: NSMakeRange(i, end))**
break;
}
}
return NSString(data: originalEntitlementsData, encoding: String.Encoding.ascii.rawValue)?.propertyList() as? NSDictionary
}
Here is the error I get:
There are a bunch of questions regarding this error, but I am not being successful implementing a solution. Any tips on how I should proceed?
Thanks guys!
Ranges are more complicated and simpler at the same time in swift.
You want subdata(in: start..<end), which makes a Range<Int>, which is the type you need. However, in this case start and end refer to the beginning and end indexes of the range, not the location and length as you pass to NSMakeRange().
As #jrturton already said, subdata(in:) takes a Range<Int> argument,
so it should be
originalEntitlementsData = originalEntitlementsData.subdata(in: i..<i+end)
in your case. But note that all the conversions to NSData, taking
the .bytes, explicit loop and memcmp are not needed if you
take advantage of the existing range(of:) method of Data:
var originalEntitlementsData = entitlementData
let xmlStart = "<?xml".data(using: .utf8)!
if let range = originalEntitlementsData.range(of: xmlStart) {
originalEntitlementsData = originalEntitlementsData.subdata(in: range.lowerBound..<originalEntitlementsData.endIndex)
// Alternatively:
// originalEntitlementsData.removeSubrange(0..<range.lowerBound)
}
I'm having trouble converting strings to and from UnsafeMutablePointers. The following code doesn't work, returning the wrong string.
// func rfcommChannelData(rfcommChannel: IOBluetoothRFCOMMChannel!, data dataPointer: UnsafeMutablePointer<Void>, length dataLength: Int)
func receivingData(data dataPointer: UnsafeMutablePointer<Void>, length dataLength: Int) {
let data = NSData(bytes: dataPointer, length: dataLength)
println("str = \(NSString(data: data, encoding: NSASCIIStringEncoding))")
}
// - (IOReturn)writeSync:(void *)data length:(UInt16)length;
func sendingData(data: UnsafeMutablePointer<Void>, length: UInt16) {
receivingData(data: data, length: Int(length))
}
var str: NSString = "Hello, playground"
var data = str.dataUsingEncoding(NSASCIIStringEncoding)!
var bytes = data.bytes
sendingData(&bytes, UInt16(data.length))
A link to the playground file is here. If anyone has experience using UnsafeMutablePointers in Swift for strings, I would very much appreciate some guidance as I have made no progress in the last few days. Thanks again!
With
var bytes = data.bytes
sendingData(&bytes, UInt16(data.length))
you pass the address of the variable bytes itself to the function, so what you see is the bytes that are used to represent that pointer.
What you probably want is
let str = "Hello, playground"
let data = str.dataUsingEncoding(NSASCIIStringEncoding)!
sendingData(UnsafeMutablePointer(data.bytes), UInt16(data.length))
to pass the pointer to the data bytes.
You should also consider
to use NSUTF8StringEncoding instead, because a conversion to
NSASCIIStringEncoding can fail.
I have decrypted using AES (CrytoSwift) and am left with an UInt8 array. What's the best approach to covert the UInt8 array into an appripriate string? Casting the array only gives back a string that looks exactly like the array. (When done in Java, a new READABLE string is obtained when casting Byte array to String).
I'm not sure if this is new to Swift 2, but at least the following works for me:
let chars: [UInt8] = [ 49, 50, 51 ]
var str = String(bytes: chars, encoding: NSUTF8StringEncoding)
In addition, if the array is formatted as a C string (trailing 0), these work:
str = String.fromCString(UnsafePointer(chars)) // UTF-8 is implicit
// or:
str = String(CString: UnsafePointer(chars), encoding: NSUTF8StringEncoding)
I don't know anything about CryptoSwift. But I can read the README:
For your convenience CryptoSwift provides two function to easily convert array of bytes to NSData and other way around:
let data = NSData.withBytes([0x01,0x02,0x03])
let bytes:[UInt8] = data.arrayOfBytes()
So my guess would be: call NSData.withBytes to get an NSData. Now you can presumably call NSString(data:encoding:) to get a string.
SWIFT 3.1
Try this:
let decData = NSData(bytes: enc, length: Int(enc.count))
let base64String = decData.base64EncodedString(options: .lineLength64Characters)
This is string output
Extensions allow you to easily modify the framework to fit your needs, essentially building your own version of Swift (my favorite part, I love to customize). Try this one out, put at the end of your view controller and call in viewDidLoad():
func stringToUInt8Extension() {
var cache : [UInt8] = []
for byte : UInt8 in 97..<97+26 {
cache.append(byte)
print(byte)
}
print("The letters of the alphabet are \(String(cache))")
}
extension String {
init(_ bytes: [UInt8]) {
self.init()
for b in bytes {
self.append(UnicodeScalar(b))
}
}
}
How do you convert a String to UInt8 array?
var str = "test"
var ar : [UInt8]
ar = str
Lots of different ways, depending on how you want to handle non-ASCII characters.
But the simplest code would be to use the utf8 view:
let string = "hello"
let array: [UInt8] = Array(string.utf8)
Note, this will result in multi-byte characters being represented as multiple entries in the array, i.e.:
let string = "é"
print(Array(string.utf8))
prints out [195, 169]
There’s also .nulTerminatedUTF8, which does the same thing, but then adds a nul-character to the end if your plan is to pass this somewhere as a C string (though if you’re doing that, you can probably also use .withCString or just use the implicit conversion for bridged C functions.
let str = "test"
let byteArray = [UInt8](str.utf8)
swift 4
func stringToUInt8Array(){
let str:String = "Swift 4"
let strToUInt8:[UInt8] = [UInt8](str.utf8)
print(strToUInt8)
}
I came to this question looking for how to convert to a Int8 array. This is how I'm doing it, but surely there's a less loopy way:
Method on an Extension for String
public func int8Array() -> [Int8] {
var retVal : [Int8] = []
for thing in self.utf16 {
retVal.append(Int8(thing))
}
return retVal
}
Note: storing a UTF-16 encoded character (2 bytes) in an Int8 (1 byte) will lead to information loss.
I considered a lot of similar questions, but still can't get the compiler to accept this.
Socket Mobile API (in Objective-C) passes ISktScanDecodedData into a delegate method in Swift (the data may be binary, which I suppose is why it's not provided as string):
func onDecodedData(device: DeviceInfo?, DecodedData d: ISktScanDecodedData?) {
let symbology: String = d!.Name()
let rawData: UnsafePointer<UInt8> = d!.getData()
let rawDataSize: UInt32 = decoded!.getDataSize()
// want a String (UTF8 is OK) or Swifty byte array...
}
In C#, this code converts the raw data into a string:
string s = Marshal.PtrToStringAuto(d.GetData(), d.GetDataSize());
In Swift, I can get as far as UnsafeArray, but then I'm stuck:
let rawArray = UnsafeArray<UInt8>(start: rawData, length: Int(rawDataSize))
Alternatively I see String.fromCString and NSString.stringWithCharacters, but neither will accept the types of arguments at hand. If I could convert from UnsafePointer<UInt8> to UnsafePointer<()>, for example, then this would be available (though I'm not sure if it would even be safe):
NSData(bytesNoCopy: UnsafePointer<()>, length: Int, freeWhenDone: Bool)
Is there an obvious way to get a string out of all this?
This should work:
let data = NSData(bytes: rawData, length: Int(rawDataSize))
let str = String(data: data, encoding: NSUTF8StringEncoding)
Update for Swift 3:
let data = Data(bytes: rawData, count: Int(rawDataSize))
let str = String(data: data, encoding: String.Encoding.utf8)
The resulting string is nil if the data does not represent
a valid UTF-8 sequence.
How about this, 'pure' Swift 2.2 instead of using NSData:
public extension String {
static func fromCString
(cs: UnsafePointer<CChar>, length: Int!) -> String?
{
if length == .None { // no length given, use \0 standard variant
return String.fromCString(cs)
}
let buflen = length + 1
var buf = UnsafeMutablePointer<CChar>.alloc(buflen)
memcpy(buf, cs, length))
buf[length] = 0 // zero terminate
let s = String.fromCString(buf)
buf.dealloc(buflen)
return s
}
}
and Swift 3:
public extension String {
static func fromCString
(cs: UnsafePointer<CChar>, length: Int!) -> String?
{
if length == nil { // no length given, use \0 standard variant
return String(cString: cs)
}
let buflen = length + 1
let buf = UnsafeMutablePointer<CChar>.allocate(capacity: buflen)
memcpy(buf, cs, length)
buf[length] = 0 // zero terminate
let s = String(cString: buf)
buf.deallocate(capacity: buflen)
return s
}
}
Admittedly it's a bit stupid to alloc a buffer and copy the data just to add the zero terminator.
Obviously, as mentioned by Zaph, you need to make sure your assumptions about the string encoding are going to be right.