Is there a way I could convert a String to an UnsafeMutablePointer<UInt8> in Swift language, avoiding data loss?
let s = "83"
var i: UInt8 = UInt8.init(s)!
let up: UnsafeMutablePointer<UInt8> = UnsafeMutablePointer<UInt8>.init(&i)
Related
I'm trying to use a library which was written in C. I've imported .a and .h files at Xcode project, and checked it works properly. I've already made them working on Objective-C, and now for Swift.
A problem I've got is functions' arguments. There's a function requires an argument widechar(defined as typedef Unsigned short int in Library), which was UnsafeMutablePointer<UInt16> in Swift. The function translates it and return the result.
So I should convert a String to UnsafeMutablePointer<UInt16>. I tried to find the right way to converting it, but I've only got converting it to UnsafeMutablePointer<UInt8>. I couldn't find answer/information about converting String to UnsafeMutablePointer<UInt16>.
Here's a source code I've written.
extension String{
var utf8CString: UnsafePointer<Int8> {
return UnsafePointer((self as NSString).utf8String!)
}
}
func translate(toBraille: String, withTable: String) -> [String]? {
let filteredString = toBraille.onlyAlphabet
let table = withTable.utf8CString
var inputLength = CInt(filteredString.count)
var outputLength = CInt(maxBufferSize)
let inputValue = UnsafeMutablePointer<widechar>.allocate(capacity: Int(outputLength))
let outputValue = UnsafeMutablePointer<widechar>.allocate(capacity: Int(outputLength))
lou_translateString(table, inputValue, &inputLength, outputValue, &outputLength, nil, nil, 0)
//This is a function that I should use.
let result:[String] = []
return result
}
You have to create an array with the UTF-16 representation of the Swift
string that you can pass to the function, and on return create
a Swift string from the UTF-16 array result.
Lets assume for simplicity that the C function is imported to Swift as
func translateString(_ source: UnsafeMutablePointer<UInt16>, _ sourceLen: UnsafeMutablePointer<CInt>,
_ dest: UnsafeMutablePointer<UInt16>, _ destLen: UnsafeMutablePointer<CInt>)
Then the following should work (explanations inline):
// Create array with UTF-16 representation of source string:
let sourceString = "Hello world"
var sourceUTF16 = Array(sourceString.utf16)
var sourceLength = CInt(sourceUTF16.count)
// Allocate array for UTF-16 representation of destination string:
let maxBufferSize = 1000
var destUTF16 = Array<UInt16>(repeating: 0, count: maxBufferSize)
var destLength = CInt(destUTF16.count)
// Call translation function:
translateString(&sourceUTF16, &sourceLength, &destUTF16, &destLength)
// Create Swift string from UTF-16 representation in destination buffer:
let destString = String(utf16CodeUnits: destUTF16, count: Int(destLength))
I have assumed that the C function updates destLength to reflect
the actual length of the translated string on return.
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
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.