get length of string in UTF8 - ios

Question

How can I get the length (not number of bytes) of a string in its UTF-8 encoded form (PHP's mb_strlen(.., 'UTF-8') equivalent)?
I tried string.characters.count but it does not return the correct length for certain characters like an emoji.
Example:
let s = "✌🏿️"
print(s.characters.count) // prints 2, but should print 3.

Answer 1

You can access the UTF-8 encoding of a string with the .utf8 property. Use count on that to get the number of UTF-8 code units in the string:
let string = "\u{1f603}" // One of the smiley face emojis...
print(string.utf8.count) // prints "4"
Based on your edited question, what you are probably looking for is the number of UnicodeScalars used to encode the string. You access that with the unicodeScalars property:
let s = "✌🏿️"
print(s.unicodeScalars.count) // prints 3
The reason everyone is confused is because your original question asks for the length of the string in its UTF-8 encoded form. The answer that you actually wanted had nothing to do with the length of the string in its UTF-8 encoded form.
I think you are confused about the difference between Unicode "extended grapheme clusters", Unicode code points, and the various encodings (like UTF-8) that can be used to encode a Unicode code point.
A Character in Swift represents what Unicode calls an "extended grapheme cluster". That is to say, it is a single visual character, even if it is made up of multiple Unicode code points.
A Unicode code point is a single linguistic symbol that is given a 32-bit value. Two or more Unicode code points can combine to create a single Character. In Swift, the Unicode code point is represented by the UnicodeScalar type.
When it comes time to store a string, or send it over the internet, or otherwise turn it into data that is represented by bytes, you have to decide how to encode it. There are all kinds of encodings, the most common is probably UTF-8, which encodes the string as a series of UInt8 values.
That's just a brief snippet of the difference between the three concepts. It is actually a really interesting subject and if you Google some of those terms, you will find a lot more good information.

Answer 2

let str = "ačŘ"
print("str has \(str.characters.count) characters") // 3
print("and \(str.utf8.count) bytes as encoded in UTF-8") // 5
update (based on your notes)
let s = "✌🏿️"
let arr:[UInt8] = [226, 156, 140, 240, 159, 143, 191, 239, 184, 143]
var arrCchar = arr.map { (uint8) -> Int8 in
Int8(bitPattern: uint8)
}
arrCchar += [0] // to be null terminated
let str = String.fromCString(&arrCchar)
print(str) // Optional("✌🏿️")
s == str // TRUE !!!!
by characters
s.characters.forEach { (c) -> () in
let str = String(c)
print(str.utf8.map{$0}, "which represents character: ", c)
str.unicodeScalars.forEach({ (u) -> () in
print("composed from unicode scalar(s): ", u.debugDescription)
})
}
/*
[226, 156, 140] which represents character: ✌
composed from unicode scalar(s): "\u{270C}"
[240, 159, 143, 191, 239, 184, 143] which represents character: 🏿️
composed from unicode scalar(s): "\u{0001F3FF}"
composed from unicode scalar(s): "\u{FE0F}"
*/
Every character in Unicode can be represented by one or more unicode scalars. A unicode scalar is a unique 21-bit number (and name) for a character or modifier, such as U+0061 for LOWERCASE LATIN LETTER A("a"), or U+1F425 for FRONT-FACING BABY CHICK ("\U0001f425").
When a Unicode string is written to a text file or some other storage, these unicode scalars are encoded in one of several Unicode-defined formats. Each format encodes the string in small chunks known as code units. These include the UTF-8 format (which encodes a string as 8-bit code units) and the UTF-16 format (which encodes a string as 16-bit code units).
//copy from Apple Developer swift programming guide