I'm using a C function in my Swift code which produces the following result (when called in Swift):
let result: UInt64 = 586512487604551679
When I call the function in C, I get:
8229a7fffffffff
However, when I convert the Swift result to hexadecimal, I get a different value.
let hex = String(result, radix: 16, uppercase: false)
print(hex) // 823b5ffffffffff
When I print from C, I use the following print statement:
printf("The index is: %" PRIx64 "\n", indexed);
What is the PRIx64 format and is that what's causing the discrepancy? In C, the value is of type uint64_t.
I've no idea what PRIx64 is. I did this:
uint64_t t = 586512487604551679;
NSString* s = [NSString stringWithFormat:#"%llx", t];
NSLog(#"%#", s); // 823b5ffffffffff
and
let t : UInt64 = 586512487604551679
let s = String(t, radix:16)
print(s) // 823b5ffffffffff
Related
I need to do bitwise OR of two binary strings.
For example, if the binary strings are "110001" and "101101", then I need the result as "111101".
How can I do this in Swift ?
You can convert it first into Int
let a = Int("110001", radix: 2)!
let b = Int("101101", radix: 2)!
let c = a | b
let stringResult = String(c, radix: 2, uppercase: false)
More info:
Int init(_:radix:)
String init(_:radix:uppercase:)
In my project, I communicate with a bluetooth device, the bluetooth device must send me a timestamp second, I received in byte:
[2,6,239]
When I convert converted to a string:
let payloadString = payload.map {
String(format: "%02x", $0)
}
Output:
["02", "06","ef"]
When I converted from the website 0206ef = 132847 seconds
How can I directly convert my aray [2,6,239] in second (= 132847 seconds)?
And if it's complicated then translate my array ["02", "06,"ef"] in second (= 132847 seconds)
The payload contains the bytes of the binary representation of the value.
You convert it back to the value by shifting each byte into its corresponding position:
let payload: [UInt8] = [2, 6, 239]
let value = Int(payload[0]) << 16 + Int(payload[1]) << 8 + Int(payload[2])
print(value) // 132847
The important point is to convert the bytes to integers before shifting, otherwise an overflow error would occur. Alternatively,
with multiplication:
let value = (Int(payload[0]) * 256 + Int(payload[1])) * 256 + Int(payload[2])
or
let value = payload.reduce(0) { $0 * 256 + Int($1) }
The last approach works with an arbitrary number of bytes – as long as
the result fits into an Int. For 4...8 bytes you better choose UInt64
to avoid overflow errors:
let value = payload.reduce(0) { $0 * 256 + UInt64($1) }
payloadString string can be reduced to hexStr and then converted to decimal
var payload = [2,6,239];
let payloadString = payload.map {
String(format: "%02x", $0)
}
//let hexStr = payloadString.reduce(""){$0 + $1}
let hexStr = payloadString.joined()
if let value = UInt64(hexStr, radix: 16) {
print(value)//132847
}
After searching for a while, I can't figure out how to get this simple result:
let byte : UInt8 = 0xF3 //Should become "F3"
I have tried this method that won't compile when passing-in either a byte or a byte array.
Two ways:
let s1 = String(byte, radix: 16, uppercase: true) // does not do 0-padding but works with
// all radices between 2 and 36
let s2 = String(format: "%02X", byte) // very similar to C
Hy everyone,
I need to transform a Int to its hexadecimal value.
Example : -40 => D8
I have a working method for positive (or unsigned) Int but it doesn't work as expected with negatives. Here's my code.
class func encodeHex(data:[Int]) -> String {
let hexadecimal = data.reduce("") { (string , element) in
var append = String(element, radix:16 , uppercase : false)
if append.characters.count == 1 {
append = "0" + append
}
return string + append
}
return hexadecimal
}
If I pass -40 I get -28.
Can anyone help ? Thanks :)
I assume from your existing code that all integers are in the range
-128 ... 127. Then this would work:
func encodeHex(data:[Int]) -> String {
return data.map { String(format: "%02hhX", $0) }.joined()
}
The "%02hhX" format prints the least significant byte of the
given integer in base 16 with 2 digits.
Example:
print(encodeHex(data: [40, -40, 127, -128]))
// 28D87F80
D8 is the last byte of binary representation of -40. The remaining three bytes are all FFs.
If you are looking for a string that represents only the last byte, you can obtain by first converting your number to unsigned 8-bit integer, and then converting it to hex, like this:
let x = UInt8(bitPattern:Int8(data))
let res = String(format:"%02X", x)
When logging-out a float in Objective-C you can do the following to limit your output to only 2 decimal places:
float avgTemp = 66.844322156
NSLog (#"average temp. = %.2f", avgTemp);
But how do you do this in Swift?
And how do you escape other characters in println in Swift?
Here's a regular Swift println statement:
println ("Avg. temp = \(avgTemp)")
So how do you limit decimal places?
Also, how do you escape double-quotes in println?
Here's the shortest solution I found thus far:
let avgTemp = 66.844322156
println(NSString(format:"%.2f", avgTemp))
Its like the swift version of NSString's stringWithFormat
Everything about the format of a number as a string can be adjusted using a NSNumberFormatter:
let nf = NSNumberFormatter()
nf.numberStyle = NSNumberFormatterStyle.DecimalStyle
nf.maximumFractionDigits = 2
println(nf.stringFromNumber(0.33333)) // prints 0.33
You can escape quotes with a backslash
println("\"God is dead\" -Nietzsche")
Println() is deprecated.
var avgTemp = 66.844322156
print("average temp. = (round(avgTemp*100)/100)") // average temp. = 66.84
//or
print(NSString(format:"average temp. = %.2f", avgTemp))) // average temp. = 66.84
avgTemp = 66.846322156
print(String(format:"average temp. = %.2f", avgTemp)) // average temp. = 66.85
If you need to print floating point numbers often with a certain precision, you could extend Float and Double with convenience methods. For example, for 2 significant figure precision:
// get Float or Double with 2 significant figure precision
var numberFormatter = NSNumberFormatter()
extension Float {
var sf2:String {
get {
numberFormatter.numberStyle = NSNumberFormatterStyle.DecimalStyle
numberFormatter.maximumSignificantDigits = 2
return numberFormatter.stringFromNumber(self)!
}
}
}
extension Double {
var sf2:String {
get {
numberFormatter.numberStyle = NSNumberFormatterStyle.DecimalStyle
numberFormatter.maximumSignificantDigits = 2
return numberFormatter.stringFromNumber(self)!
}
}
}
Then when you need to print things:
let x = 5.23325
print("The value of x is \(x.sf2)")