Swift get character at index

Swift get character at index DEFAULT

How to get an index of a character in Swift String

In swift, we can use the method to get the position of a character in a given string.

In this below example, we are finding an character index.

Swift 5 replaces with .

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Sours: https://www.codegrepper.com/code-examples/swift/java+string+get+character+at+specific+index
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Very often I find myself trying to access a character in string using a given index, however due to the way strings are implemented in Swift, it’s not that easy.

Ideally, given a string, I’d like to access a character at index 3 like this:

Unfortunately, this won’t work and the compiler will throw the following error:

‘subscript(_:)’ is unavailable: cannot subscript String with an Int, use a String.Index instead.

The correct way of getting a character at index 3 involves using String.Index:

Using the above method everywhere in your project would end up cluttering your code. By creating an extension to the StringProtocol and implementing the subscript method, we can bring this functionality into every String (and Substring) in Swift.

Here is the full code of the extension:

Which can be used just like we originally wanted to:

If you’d like to convert the character back to string, cast it like that:

Related tutorials:

Check out Apple’s official documentation of String.

 

Sours: https://www.simpleswiftguide.com/get-character-from-string-using-its-index-in-swift/
Why can't you use an Int index in Strings? #SwiftLang

Strings and Characters¶

A string is a series of characters, such as or . Swift strings are represented by the type. The contents of a can be accessed in various ways, including as a collection of values.

Swift’s and types provide a fast, Unicode-compliant way to work with text in your code. The syntax for string creation and manipulation is lightweight and readable, with a string literal syntax that’s similar to C. String concatenation is as simple as combining two strings with the operator, and string mutability is managed by choosing between a constant or a variable, just like any other value in Swift. You can also use strings to insert constants, variables, literals, and expressions into longer strings, in a process known as string interpolation. This makes it easy to create custom string values for display, storage, and printing.

Despite this simplicity of syntax, Swift’s type is a fast, modern string implementation. Every string is composed of encoding-independent Unicode characters, and provides support for accessing those characters in various Unicode representations.

Note

Swift’s type is bridged with Foundation’s class. Foundation also extends to expose methods defined by . This means, if you import Foundation, you can access those methods on without casting.

For more information about using with Foundation and Cocoa, see Bridging Between String and NSString.

String Literals¶

You can include predefined values within your code as string literals. A string literal is a sequence of characters surrounded by double quotation marks ().

Use a string literal as an initial value for a constant or variable:

  1. letsomeString = "Some string literal value"

Note that Swift infers a type of for the constant because it’s initialized with a string literal value.

Multiline String Literals¶

If you need a string that spans several lines, use a multiline string literal—a sequence of characters surrounded by three double quotation marks:

  1. letquotation = """
  2. The White Rabbit put on his spectacles. "Where shall I begin,
  3. please your Majesty?" he asked.
  4. "Begin at the beginning," the King said gravely, "and go on
  5. till you come to the end; then stop."
  6. """

A multiline string literal includes all of the lines between its opening and closing quotation marks. The string begins on the first line after the opening quotation marks () and ends on the line before the closing quotation marks, which means that neither of the strings below start or end with a line break:

  1. letsingleLineString = "These are the same."
  2. letmultilineString = """
  3. These are the same.
  4. """

When your source code includes a line break inside of a multiline string literal, that line break also appears in the string’s value. If you want to use line breaks to make your source code easier to read, but you don’t want the line breaks to be part of the string’s value, write a backslash () at the end of those lines:

  1. letsoftWrappedQuotation = """
  2. The White Rabbit put on his spectacles. "Where shall I begin, \
  3. please your Majesty?" he asked.
  4. "Begin at the beginning," the King said gravely, "and go on \
  5. till you come to the end; then stop."
  6. """

To make a multiline string literal that begins or ends with a line feed, write a blank line as the first or last line. For example:

  1. letlineBreaks = """
  2. This string starts with a line break.
  3. It also ends with a line break.
  4. """

A multiline string can be indented to match the surrounding code. The whitespace before the closing quotation marks () tells Swift what whitespace to ignore before all of the other lines. However, if you write whitespace at the beginning of a line in addition to what’s before the closing quotation marks, that whitespace is included.

../_images/multilineStringWhitespace_2x.png

In the example above, even though the entire multiline string literal is indented, the first and last lines in the string don’t begin with any whitespace. The middle line has more indentation than the closing quotation marks, so it starts with that extra four-space indentation.

Special Characters in String Literals¶

String literals can include the following special characters:

  • The escaped special characters (null character), (backslash), (horizontal tab), (line feed), (carriage return), (double quotation mark) and (single quotation mark)
  • An arbitrary Unicode scalar value, written as n, where n is a 1–8 digit hexadecimal number (Unicode is discussed in Unicode below)

The code below shows four examples of these special characters. The constant contains two escaped double quotation marks. The , , and constants demonstrate the Unicode scalar format:

  1. letwiseWords = "\"Imagination is more important than knowledge\" - Einstein"
  2. // "Imagination is more important than knowledge" - Einstein
  3. letdollarSign = "\u{24}"// $, Unicode scalar U+0024
  4. letblackHeart = "\u{2665}"// ♥, Unicode scalar U+2665
  5. letsparklingHeart = "\u{1F496}"// 💖, Unicode scalar U+1F496

Because multiline string literals use three double quotation marks instead of just one, you can include a double quotation mark () inside of a multiline string literal without escaping it. To include the text in a multiline string, escape at least one of the quotation marks. For example:

  1. letthreeDoubleQuotationMarks = """
  2. Escaping the first quotation mark \"""
  3. Escaping all three quotation marks \"\"\"
  4. """

Extended String Delimiters¶

You can place a string literal within extended delimiters to include special characters in a string without invoking their effect. You place your string within quotation marks () and surround that with number signs (). For example, printing the string literal prints the line feed escape sequence () rather than printing the string across two lines.

If you need the special effects of a character in a string literal, match the number of number signs within the string following the escape character (). For example, if your string is and you want to break the line, you can use instead. Similarly, also breaks the line.

String literals created using extended delimiters can also be multiline string literals. You can use extended delimiters to include the text in a multiline string, overriding the default behavior that ends the literal. For example:

  1. letthreeMoreDoubleQuotationMarks = #"""
  2. Here are three more double quotes: """
  3. """#

Initializing an Empty String¶

To create an empty value as the starting point for building a longer string, either assign an empty string literal to a variable, or initialize a new instance with initializer syntax:

  1. varemptyString = ""// empty string literal
  2. varanotherEmptyString = String() // initializer syntax
  3. // these two strings are both empty, and are equivalent to each other

Find out whether a value is empty by checking its Boolean property:

  1. ifemptyString.isEmpty {
  2. print("Nothing to see here")
  3. }
  4. // Prints "Nothing to see here"

String Mutability¶

You indicate whether a particular can be modified (or mutated) by assigning it to a variable (in which case it can be modified), or to a constant (in which case it can’t be modified):

  1. varvariableString = "Horse"
  2. variableString += " and carriage"
  3. // variableString is now "Horse and carriage"
  4. letconstantString = "Highlander"
  5. constantString += " and another Highlander"
  6. // this reports a compile-time error - a constant string cannot be modified

Note

This approach is different from string mutation in Objective-C and Cocoa, where you choose between two classes ( and ) to indicate whether a string can be mutated.

Strings Are Value Types¶

Swift’s type is a value type. If you create a new value, that value is copied when it’s passed to a function or method, or when it’s assigned to a constant or variable. In each case, a new copy of the existing value is created, and the new copy is passed or assigned, not the original version. Value types are described in Structures and Enumerations Are Value Types.

Swift’s copy-by-default behavior ensures that when a function or method passes you a value, it’s clear that you own that exact value, regardless of where it came from. You can be confident that the string you are passed won’t be modified unless you modify it yourself.

Behind the scenes, Swift’s compiler optimizes string usage so that actual copying takes place only when absolutely necessary. This means you always get great performance when working with strings as value types.

Working with Characters¶

You can access the individual values for a by iterating over the string with a - loop:

  1. forcharacterin"Dog!🐶" {
  2. print(character)
  3. }
  4. // D
  5. // o
  6. // g
  7. // !
  8. // 🐶

The - loop is described in For-In Loops.

Alternatively, you can create a stand-alone constant or variable from a single-character string literal by providing a type annotation:

  1. letexclamationMark: Character = "!"

values can be constructed by passing an array of values as an argument to its initializer:

  1. letcatCharacters: [Character] = ["C", "a", "t", "!", "🐱"]
  2. letcatString = String(catCharacters)
  3. print(catString)
  4. // Prints "Cat!🐱"

Concatenating Strings and Characters¶

values can be added together (or concatenated) with the addition operator () to create a new value:

  1. letstring1 = "hello"
  2. letstring2 = " there"
  3. varwelcome = string1 + string2
  4. // welcome now equals "hello there"

You can also append a value to an existing variable with the addition assignment operator ():

  1. varinstruction = "look over"
  2. instruction += string2
  3. // instruction now equals "look over there"

You can append a value to a variable with the type’s method:

  1. letexclamationMark: Character = "!"
  2. welcome.append(exclamationMark)
  3. // welcome now equals "hello there!"

Note

You can’t append a or to an existing variable, because a value must contain a single character only.

If you’re using multiline string literals to build up the lines of a longer string, you want every line in the string to end with a line break, including the last line. For example:

  1. letbadStart = """
  2. one
  3. two
  4. """
  5. letend = """
  6. three
  7. """
  8. print(badStart + end)
  9. // Prints two lines:
  10. // one
  11. // twothree
  12. letgoodStart = """
  13. one
  14. two
  15. """
  16. print(goodStart + end)
  17. // Prints three lines:
  18. // one
  19. // two
  20. // three

In the code above, concatenating with produces a two-line string, which isn’t the desired result. Because the last line of doesn’t end with a line break, that line gets combined with the first line of . In contrast, both lines of end with a line break, so when it’s combined with the result has three lines, as expected.

String Interpolation¶

String interpolation is a way to construct a new value from a mix of constants, variables, literals, and expressions by including their values inside a string literal. You can use string interpolation in both single-line and multiline string literals. Each item that you insert into the string literal is wrapped in a pair of parentheses, prefixed by a backslash ():

  1. letmultiplier = 3
  2. letmessage = "\(multiplier) times 2.5 is \(Double(multiplier) * 2.5)"
  3. // message is "3 times 2.5 is 7.5"

In the example above, the value of is inserted into a string literal as . This placeholder is replaced with the actual value of when the string interpolation is evaluated to create an actual string.

The value of is also part of a larger expression later in the string. This expression calculates the value of and inserts the result () into the string. In this case, the expression is written as when it’s included inside the string literal.

You can use extended string delimiters to create strings containing characters that would otherwise be treated as a string interpolation. For example:

  1. print(#"Write an interpolated string in Swift using \(multiplier)."#)
  2. // Prints "Write an interpolated string in Swift using \(multiplier)."

To use string interpolation inside a string that uses extended delimiters, match the number of number signs after the backslash to the number of number signs at the beginning and end of the string. For example:

  1. print(#"6 times 7 is \#(6 * 7)."#)
  2. // Prints "6 times 7 is 42."

Note

The expressions you write inside parentheses within an interpolated string can’t contain an unescaped backslash (), a carriage return, or a line feed. However, they can contain other string literals.

Unicode¶

Unicode is an international standard for encoding, representing, and processing text in different writing systems. It enables you to represent almost any character from any language in a standardized form, and to read and write those characters to and from an external source such as a text file or web page. Swift’s and types are fully Unicode-compliant, as described in this section.

Unicode Scalar Values¶

Behind the scenes, Swift’s native type is built from Unicode scalar values. A Unicode scalar value is a unique 21-bit number for a character or modifier, such as for (), or for ().

Note that not all 21-bit Unicode scalar values are assigned to a character—some scalars are reserved for future assignment or for use in UTF-16 encoding. Scalar values that have been assigned to a character typically also have a name, such as and in the examples above.

Extended Grapheme Clusters¶

Every instance of Swift’s type represents a single extended grapheme cluster. An extended grapheme cluster is a sequence of one or more Unicode scalars that (when combined) produce a single human-readable character.

Here’s an example. The letter can be represented as the single Unicode scalar (, or ). However, the same letter can also be represented as a pair of scalars—a standard letter (, or ), followed by the scalar (). The scalar is graphically applied to the scalar that precedes it, turning an into an when it’s rendered by a Unicode-aware text-rendering system.

In both cases, the letter is represented as a single Swift value that represents an extended grapheme cluster. In the first case, the cluster contains a single scalar; in the second case, it’s a cluster of two scalars:

  1. leteAcute: Character = "\u{E9}"// é
  2. letcombinedEAcute: Character = "\u{65}\u{301}"// e followed by ́
  3. // eAcute is é, combinedEAcute is é

Extended grapheme clusters are a flexible way to represent many complex script characters as a single value. For example, Hangul syllables from the Korean alphabet can be represented as either a precomposed or decomposed sequence. Both of these representations qualify as a single value in Swift:

  1. letprecomposed: Character = "\u{D55C}"// 한
  2. letdecomposed: Character = "\u{1112}\u{1161}\u{11AB}"// ᄒ, ᅡ, ᆫ
  3. // precomposed is 한, decomposed is 한

Extended grapheme clusters enable scalars for enclosing marks (such as , or ) to enclose other Unicode scalars as part of a single value:

  1. letenclosedEAcute: Character = "\u{E9}\u{20DD}"
  2. // enclosedEAcute is é⃝

Unicode scalars for regional indicator symbols can be combined in pairs to make a single value, such as this combination of () and ():

  1. letregionalIndicatorForUS: Character = "\u{1F1FA}\u{1F1F8}"
  2. // regionalIndicatorForUS is 🇺🇸

Counting Characters¶

To retrieve a count of the values in a string, use the property of the string:

  1. letunusualMenagerie = "Koala 🐨, Snail 🐌, Penguin 🐧, Dromedary 🐪"
  2. print("unusualMenagerie has \(unusualMenagerie.count) characters")
  3. // Prints "unusualMenagerie has 40 characters"

Note that Swift’s use of extended grapheme clusters for values means that string concatenation and modification may not always affect a string’s character count.

For example, if you initialize a new string with the four-character word , and then append a () to the end of the string, the resulting string will still have a character count of , with a fourth character of , not :

  1. varword = "cafe"
  2. print("the number of characters in \(word) is \(word.count)")
  3. // Prints "the number of characters in cafe is 4"
  4. word += "\u{301}"// COMBINING ACUTE ACCENT, U+0301
  5. print("the number of characters in \(word) is \(word.count)")
  6. // Prints "the number of characters in café is 4"

Note

Extended grapheme clusters can be composed of multiple Unicode scalars. This means that different characters—and different representations of the same character—can require different amounts of memory to store. Because of this, characters in Swift don’t each take up the same amount of memory within a string’s representation. As a result, the number of characters in a string can’t be calculated without iterating through the string to determine its extended grapheme cluster boundaries. If you are working with particularly long string values, be aware that the property must iterate over the Unicode scalars in the entire string in order to determine the characters for that string.

The count of the characters returned by the property isn’t always the same as the property of an that contains the same characters. The length of an is based on the number of 16-bit code units within the string’s UTF-16 representation and not the number of Unicode extended grapheme clusters within the string.

Accessing and Modifying a String¶

You access and modify a string through its methods and properties, or by using subscript syntax.

String Indices¶

Each value has an associated index type, , which corresponds to the position of each in the string.

As mentioned above, different characters can require different amounts of memory to store, so in order to determine which is at a particular position, you must iterate over each Unicode scalar from the start or end of that . For this reason, Swift strings can’t be indexed by integer values.

Use the property to access the position of the first of a . The property is the position after the last character in a . As a result, the property isn’t a valid argument to a string’s subscript. If a is empty, and are equal.

You access the indices before and after a given index using the and methods of . To access an index farther away from the given index, you can use the method instead of calling one of these methods multiple times.

You can use subscript syntax to access the at a particular index.

  1. letgreeting = "Guten Tag!"
  2. greeting[greeting.startIndex]
  3. // G
  4. greeting[greeting.index(before: greeting.endIndex)]
  5. // !
  6. greeting[greeting.index(after: greeting.startIndex)]
  7. // u
  8. letindex = greeting.index(greeting.startIndex, offsetBy: 7)
  9. greeting[index]
  10. // a

Attempting to access an index outside of a string’s range or a at an index outside of a string’s range will trigger a runtime error.

  1. greeting[greeting.endIndex] // Error
  2. greeting.index(after: greeting.endIndex) // Error

Use the property to access all of the indices of individual characters in a string.

  1. forindexingreeting.indices {
  2. print("\(greeting[index]) ", terminator: "")
  3. }
  4. // Prints "G u t e n T a g ! "

Note

You can use the and properties and the , , and methods on any type that conforms to the protocol. This includes , as shown here, as well as collection types such as , , and .

Inserting and Removing¶

To insert a single character into a string at a specified index, use the method, and to insert the contents of another string at a specified index, use the method.

  1. varwelcome = "hello"
  2. welcome.insert("!", at: welcome.endIndex)
  3. // welcome now equals "hello!"
  4. welcome.insert(contentsOf: " there", at: welcome.index(before: welcome.endIndex))
  5. // welcome now equals "hello there!"

To remove a single character from a string at a specified index, use the method, and to remove a substring at a specified range, use the method:

  1. welcome.remove(at: welcome.index(before: welcome.endIndex))
  2. // welcome now equals "hello there"
  3. letrange = welcome.index(welcome.endIndex, offsetBy: -6)..<welcome.endIndex
  4. welcome.removeSubrange(range)
  5. // welcome now equals "hello"

Note

You can use the , , , and methods on any type that conforms to the protocol. This includes , as shown here, as well as collection types such as , , and .

Substrings¶

When you get a substring from a string—for example, using a subscript or a method like —the result is an instance of , not another string. Substrings in Swift have most of the same methods as strings, which means you can work with substrings the same way you work with strings. However, unlike strings, you use substrings for only a short amount of time while performing actions on a string. When you’re ready to store the result for a longer time, you convert the substring to an instance of . For example:

  1. letgreeting = "Hello, world!"
  2. letindex = greeting.firstIndex(of: ",") ?? greeting.endIndex
  3. letbeginning = greeting[..<index]
  4. // beginning is "Hello"
  5. // Convert the result to a String for long-term storage.
  6. letnewString = String(beginning)

Like strings, each substring has a region of memory where the characters that make up the substring are stored. The difference between strings and substrings is that, as a performance optimization, a substring can reuse part of the memory that’s used to store the original string, or part of the memory that’s used to store another substring. (Strings have a similar optimization, but if two strings share memory, they’re equal.) This performance optimization means you don’t have to pay the performance cost of copying memory until you modify either the string or substring. As mentioned above, substrings aren’t suitable for long-term storage—because they reuse the storage of the original string, the entire original string must be kept in memory as long as any of its substrings are being used.

In the example above, is a string, which means it has a region of memory where the characters that make up the string are stored. Because is a substring of , it reuses the memory that uses. In contrast, is a string—when it’s created from the substring, it has its own storage. The figure below shows these relationships:

../_images/stringSubstring_2x.png

Note

Both and conform to the protocol, which means it’s often convenient for string-manipulation functions to accept a value. You can call such functions with either a or value.

Comparing Strings¶

Swift provides three ways to compare textual values: string and character equality, prefix equality, and suffix equality.

String and Character Equality¶

String and character equality is checked with the “equal to” operator () and the “not equal to” operator (), as described in Comparison Operators:

  1. letquotation = "We're a lot alike, you and I."
  2. letsameQuotation = "We're a lot alike, you and I."
  3. ifquotation == sameQuotation {
  4. print("These two strings are considered equal")
  5. }
  6. // Prints "These two strings are considered equal"

Two values (or two values) are considered equal if their extended grapheme clusters are canonically equivalent. Extended grapheme clusters are canonically equivalent if they have the same linguistic meaning and appearance, even if they’re composed from different Unicode scalars behind the scenes.

For example, () is canonically equivalent to () followed by (). Both of these extended grapheme clusters are valid ways to represent the character , and so they’re considered to be canonically equivalent:

  1. // "Voulez-vous un café?" using LATIN SMALL LETTER E WITH ACUTE
  2. leteAcuteQuestion = "Voulez-vous un caf\u{E9}?"
  3. // "Voulez-vous un café?" using LATIN SMALL LETTER E and COMBINING ACUTE ACCENT
  4. letcombinedEAcuteQuestion = "Voulez-vous un caf\u{65}\u{301}?"
  5. ifeAcuteQuestion == combinedEAcuteQuestion {
  6. print("These two strings are considered equal")
  7. }
  8. // Prints "These two strings are considered equal"

Conversely, (, or ), as used in English, is not equivalent to (, or ), as used in Russian. The characters are visually similar, but don’t have the same linguistic meaning:

  1. letlatinCapitalLetterA: Character = "\u{41}"
  2. letcyrillicCapitalLetterA: Character = "\u{0410}"
  3. iflatinCapitalLetterA != cyrillicCapitalLetterA {
  4. print("These two characters aren't equivalent.")
  5. }
  6. // Prints "These two characters aren't equivalent."

Note

String and character comparisons in Swift aren’t locale-sensitive.

Prefix and Suffix Equality¶

To check whether a string has a particular string prefix or suffix, call the string’s and methods, both of which take a single argument of type and return a Boolean value.

The examples below consider an array of strings representing the scene locations from the first two acts of Shakespeare’s Romeo and Juliet:

  1. letromeoAndJuliet = [
  2. "Act 1 Scene 1: Verona, A public place",
  3. "Act 1 Scene 2: Capulet's mansion",
  4. "Act 1 Scene 3: A room in Capulet's mansion",
  5. "Act 1 Scene 4: A street outside Capulet's mansion",
  6. "Act 1 Scene 5: The Great Hall in Capulet's mansion",
  7. "Act 2 Scene 1: Outside Capulet's mansion",
  8. "Act 2 Scene 2: Capulet's orchard",
  9. "Act 2 Scene 3: Outside Friar Lawrence's cell",
  10. "Act 2 Scene 4: A street in Verona",
  11. "Act 2 Scene 5: Capulet's mansion",
  12. "Act 2 Scene 6: Friar Lawrence's cell"
  13. ]

You can use the method with the array to count the number of scenes in Act 1 of the play:

  1. varact1SceneCount = 0
  2. forsceneinromeoAndJuliet {
  3. ifscene.hasPrefix("Act 1 ") {
  4. act1SceneCount += 1
  5. }
  6. }
  7. print("There are \(act1SceneCount) scenes in Act 1")
  8. // Prints "There are 5 scenes in Act 1"

Similarly, use the method to count the number of scenes that take place in or around Capulet’s mansion and Friar Lawrence’s cell:

  1. varmansionCount = 0
  2. varcellCount = 0
  3. forsceneinromeoAndJuliet {
  4. ifscene.hasSuffix("Capulet's mansion") {
  5. mansionCount += 1
  6. } elseifscene.hasSuffix("Friar Lawrence's cell") {
  7. cellCount += 1
  8. }
  9. }
  10. print("\(mansionCount) mansion scenes; \(cellCount) cell scenes")
  11. // Prints "6 mansion scenes; 2 cell scenes"

Note

The and methods perform a character-by-character canonical equivalence comparison between the extended grapheme clusters in each string, as described in String and Character Equality.

Unicode Representations of Strings¶

When a Unicode string is written to a text file or some other storage, the Unicode scalars in that string are encoded in one of several Unicode-defined encoding forms. Each form encodes the string in small chunks known as code units. These include the UTF-8 encoding form (which encodes a string as 8-bit code units), the UTF-16 encoding form (which encodes a string as 16-bit code units), and the UTF-32 encoding form (which encodes a string as 32-bit code units).

Swift provides several different ways to access Unicode representations of strings. You can iterate over the string with a - statement, to access its individual values as Unicode extended grapheme clusters. This process is described in Working with Characters.

Alternatively, access a value in one of three other Unicode-compliant representations:

  • A collection of UTF-8 code units (accessed with the string’s property)
  • A collection of UTF-16 code units (accessed with the string’s property)
  • A collection of 21-bit Unicode scalar values, equivalent to the string’s UTF-32 encoding form (accessed with the string’s property)

Each example below shows a different representation of the following string, which is made up of the characters , , , (, or Unicode scalar ), and the 🐶 character (, or Unicode scalar ):

  1. letdogString = "Dog‼🐶"

UTF-8 Representation¶

You can access a UTF-8 representation of a by iterating over its property. This property is of type , which is a collection of unsigned 8-bit () values, one for each byte in the string’s UTF-8 representation:

../_images/UTF8_2x.png
  1. forcodeUnitindogString.utf8 {
  2. print("\(codeUnit) ", terminator: "")
  3. }
  4. print("")
  5. // Prints "68 111 103 226 128 188 240 159 144 182 "

In the example above, the first three decimal values (, , ) represent the characters , , and , whose UTF-8 representation is the same as their ASCII representation. The next three decimal values (, , ) are a three-byte UTF-8 representation of the character. The last four values (, , , ) are a four-byte UTF-8 representation of the character.

UTF-16 Representation¶

You can access a UTF-16 representation of a by iterating over its property. This property is of type , which is a collection of unsigned 16-bit () values, one for each 16-bit code unit in the string’s UTF-16 representation:

../_images/UTF16_2x.png
  1. forcodeUnitindogString.utf16 {
  2. print("\(codeUnit) ", terminator: "")
  3. }
  4. print("")
  5. // Prints "68 111 103 8252 55357 56374 "

Again, the first three values (, , ) represent the characters , , and , whose UTF-16 code units have the same values as in the string’s UTF-8 representation (because these Unicode scalars represent ASCII characters).

The fourth value () is a decimal equivalent of the hexadecimal value , which represents the Unicode scalar for the character. This character can be represented as a single code unit in UTF-16.

The fifth and sixth values ( and ) are a UTF-16 surrogate pair representation of the character. These values are a high-surrogate value of (decimal value ) and a low-surrogate value of (decimal value ).

Unicode Scalar Representation¶

You can access a Unicode scalar representation of a value by iterating over its property. This property is of type , which is a collection of values of type .

Each has a property that returns the scalar’s 21-bit value, represented within a value:

../_images/UnicodeScalar_2x.png
  1. forscalarindogString.unicodeScalars {
  2. print("\(scalar.value) ", terminator: "")
  3. }
  4. print("")
  5. // Prints "68 111 103 8252 128054 "

The properties for the first three values (, , ) once again represent the characters , , and .

The fourth value () is again a decimal equivalent of the hexadecimal value , which represents the Unicode scalar for the character.

The property of the fifth and final , , is a decimal equivalent of the hexadecimal value , which represents the Unicode scalar for the character.

As an alternative to querying their properties, each value can also be used to construct a new value, such as with string interpolation:

  1. forscalarindogString.unicodeScalars {
  2. print("\(scalar) ")
  3. }
  4. // D
  5. // o
  6. // g
  7. // ‼
  8. // 🐶
Sours: https://docs.swift.org/swift-book/LanguageGuide/StringsAndCharacters.html

Character swift index get at

Get nth character of a string in Swift programming language

Attention: Please see Leo Dabus' answer for a proper implementation for Swift 4 and Swift 5.

Swift 4 or later

The type was introduced in Swift 4 to make substrings faster and more efficient by sharing storage with the original string, so that's what the subscript functions should return.

Try it out here

To convert the into a , you can simply do , but you should only do that if you plan to keep the substring around. Otherwise, it's more efficient to keep it a .

It would be great if someone could figure out a good way to merge these two extensions into one. I tried extending without success, because the method does not exist there. Note: This answer has been already edited, it is properly implemented and now works for substrings as well. Just make sure to use a valid range to avoid crashing when subscripting your StringProtocol type. For subscripting with a range that won't crash with out of range values you can use this implementation


Why is this not built-in?

The error message says "see the documentation comment for discussion". Apple provides the following explanation in the file UnavailableStringAPIs.swift:

Subscripting strings with integers is not available.

The concept of "the th character in a string" has different interpretations in different libraries and system components. The correct interpretation should be selected according to the use case and the APIs involved, so cannot be subscripted with an integer.

Swift provides several different ways to access the character data stored inside strings.

  • is a collection of UTF-8 code units in the string. Use this API when converting the string to UTF-8. Most POSIX APIs process strings in terms of UTF-8 code units.

  • is a collection of UTF-16 code units in string. Most Cocoa and Cocoa touch APIs process strings in terms of UTF-16 code units. For example, instances of used with and store substring offsets and lengths in terms of UTF-16 code units.

  • is a collection of Unicode scalars. Use this API when you are performing low-level manipulation of character data.

  • is a collection of extended grapheme clusters, which are an approximation of user-perceived characters.

Note that when processing strings that contain human-readable text, character-by-character processing should be avoided to the largest extent possible. Use high-level locale-sensitive Unicode algorithms instead, for example, , , etc.

Sours: https://stackoverflow.com/questions/24092884/get-nth-character-of-a-string-in-swift-programming-language
How To Limit Characters in a UITextField w/ Character Counter (Swift 2.0/Xcode 7)

Get Nth character in string with Swift

This is something that annoys me to this day with Swift. This is a simple task with other languages. JavaScript and Java can use and other languages like Python(actually JavaScript too) you can get a character using a simple index like you would with an array, eg, .

Apple has a reason for doing this as you can see here but even so, I find it annoying and I can never remember how to do it.

After researching how to do this I came across an StackOverflow post. This post has the correct answer, but I learned more than just getting a from a . In this post I will go through the ways listed in the SO post to better understand it.

It seems that there was a way suggested in the String manifesto to do this, but unfortunately, that does not work anymore. This is the suggestion from the manifesto:

String Extension

This solution creates a extension. This is what I would normally do, and what I was planning on writing this post about. Below is an example.

To get the character using an extension, you can use the following code:

This is a simple extension that will get the at a specific index and it works well, the issue I have with this is that it returns a . Normally if I want to get the character at an index, I actually want the value to be a and not a .

I updated it by creating a new instance of a string using the that we would have returned in the above example. This is the updated code:

Substring

I must say, before today I didn't even know about in Swift. I have never really needed to use in Swift.

From research it seems that a might be more efficient. This is a snippet from the documentation on

Operating on substrings is fast and efficient because a substring shares its storage with the original string

It seems like it might be a good idea to get the character as a . The other benefit is that a has the same interface as a , this is what the Apple documentation says:

The `Substring` type presents the same interface as `String`, so you can avoid or defer any copying of the string's contents

Now that we have this information we can do this:

From my testing this gave me the same results as the previous two examples. There is one thing with using a and that can also be found in the documentation.

Important: Don't store substrings longer than you need them to perform a specific operation. A substring holds a reference to the entire storage of the string it comes from, not just to the portion it presents, even when there is no other reference to the original string. Storing substrings may, therefore, prolong the lifetime of string data that is no longer otherwise accessible, which can appear to be memory leakage.

StringProtocol

As I said, most of these solutions are based on solutions provided by the StackOverflow article I referenced in the beginning of this post.

Unlike , I had heard of before, but I had never worked with it. According to StackOverflow, this is the best way to do it. So I took a look at the documentation for and the first and only line of documentation says this:

A type that can represent a string as a collection of characters

Sounds like the perfect solution, so lets see what it looks like.

It is pretty much the same as the other solutions. I am showing the version, but you could return a character in the same way we did when we made the extension.

You could also do the method that we have gone through above, but you will need to make the return type an optional or force unwrap it when returning.

This is the code with the returning a :

I personally prefer keeping the return value as optional, but if you want you could force unwrap it.

Conclusion

This was an interesting post for me. I never thought there would be so many techniques to get the nth character from a string.

Sours: https://programmingwithswift.com/get-nth-character-in-string-with-swift/

You will also like:

Finding index of character in Swift String

You are not the only one who couldn't find the solution.

doesn't implement . Probably because they enable characters with different byte lengths. That's why we have to use ( or in Swift 1.x) to get the number of characters. That also applies to positions. The is probably an index into the raw array of bytes and they don't want to expose that. The is meant to protect us from accessing bytes in the middle of characters.

That means that any index you get must be created from or ( implements ). Any other indices can be created using or methods.

Now to help us with indices, there is a set of methods (functions in Swift 1.x):

Swift 4.x

Swift 3.0

Swift 2.x

Swift 1.x

Working with is cumbersome but using a wrapper to index by integers (see https://stackoverflow.com/a/25152652/669586) is dangerous because it hides the inefficiency of real indexing.

Note that Swift indexing implementation has the problem that indices/ranges created for one string cannot be reliably used for a different string, for example:

Swift 2.x

Swift 1.x


Swift 3.0 makes this a bit more verbose:

Extension:


In Swift 2.0 this has become easier:

Extension:


Swift 1.x implementation:

For a pure Swift solution one can use:

As an extension to :


Sours: https://newbedev.com/finding-index-of-character-in-swift-string


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