# Strings and Characters > A string is a series of characters, such as "hello, world" or "albatross". Swift strings are represented by the String type. - Skill: `tools-only/strings-and-characters` (Agent Skill, multi-file: 3 files) - Install (CLI): `npx skillmds@latest add tools-only/strings-and-characters` - Raw SKILL.md: https://api.skillmd.com/api/skills/tools-only/strings-and-characters/raw - Safety review: pending (external: skill-scanner PASS, skillspector CAUTION) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: tools-only (https://skillmd.com/u/tools-only) - Updated: 2026-09-29 - Page: https://skillmd.com/skills/tools-only/strings-and-characters --- # Strings and Characters Store and manipulate text. A *string* is a series of characters, such as `"hello, world"` or `"albatross"`. Swift strings are represented by the `String` type. The contents of a `String` can be accessed in various ways, including as a collection of `Character` values. Swift's `String` and `Character` 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 `String` 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 `String` type is bridged with Foundation's `NSString` class. > Foundation also extends `String` to expose methods defined by `NSString`. > This means, if you import Foundation, > you can access those `NSString` methods on `String` without casting. > > For more information about using `String` with Foundation and Cocoa, > see [Bridging Between String and NSString](https://developer.apple.com/documentation/swift/string#2919514). ## String Literals You can include predefined `String` 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: ```swift let someString = "Some string literal value" ``` Note that Swift infers a type of `String` for the `someString` 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: ```swift let quotation = """ The White Rabbit put on his spectacles. "Where shall I begin, please your Majesty?" he asked. "Begin at the beginning," the King said gravely, "and go on till you come to the end; then stop." """ ``` 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: ```swift let singleLineString = "These are the same." let multilineString = """ These are the same. """ ``` 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: ```swift let softWrappedQuotation = """ The White Rabbit put on his spectacles. "Where shall I begin, \ please your Majesty?" he asked. "Begin at the beginning," the King said gravely, "and go on \ till you come to the end; then stop." """ ``` 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: ```swift let lineBreaks = """ This string starts with a line break. It also ends with a line break. """ ``` 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. ![](multilineStringWhitespace) 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 `\0` (null character), `\\` (backslash), `\t` (horizontal tab), `\n` (line feed), `\r` (carriage return), `\"` (double quotation mark) and `'` (single quotation mark) - An arbitrary Unicode scalar value, written as `\u{`*n*`}`, where *n* is a 1--8 digit hexadecimal number (Unicode is discussed in below) The code below shows four examples of these special characters. The `wiseWords` constant contains two escaped double quotation marks. The `dollarSign`, `blackHeart`, and `sparklingHeart` constants demonstrate the Unicode scalar format: ```swift let wiseWords = "\"Imagination is more important than knowledge\" - Einstein" // "Imagination is more important than knowledge" - Einstein let dollarSign = "\u{24}" // $, Unicode scalar U+0024 let blackHeart = "\u{2665}" // ♥, Unicode scalar U+2665 let sparklingHeart = "\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: ```swift let threeDoubleQuotationMarks = """ Escaping the first quotation mark \""" Escaping all three quotation marks \"\"\" """ ``` ### 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 `#"Line 1\nLine 2"#` prints the line feed escape sequence (`\n`) 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 `#"Line 1\nLine 2"#` and you want to break the line, you can use `#"Line 1\#nLine 2"#` instead. Similarly, `###"Line1\###nLine2"###` 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: ```swift let threeMoreDoubleQuotationMarks = #""" Here are three more double quotes: """ """# ``` ## Initializing an Empty String To create an empty `String` value as the starting point for building a longer string, either assign an empty string literal to a variable or initialize a new `String` instance with initializer syntax: ```swift var emptyString = "" // empty string literal var anotherEmptyString = String() // initializer syntax // these two strings are both empty, and are equivalent to each other ``` Find out whether a `String` value is empty by checking its Boolean `isEmpty` property: ```swift if emptyString.isEmpty { print("Nothing to see here") } // Prints "Nothing to see here". ``` ## String Mutability You indicate whether a particular `String` 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): ```swift var variableString = "Horse" variableString += " and carriage" // variableString is now "Horse and carriage" let constantString = "Highlander" constantString += " and another Highlander" // 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 (`NSString` and `NSMutableString`) > to indicate whether a string can be mutated. ## Strings Are Value Types Swift's `String` type is a *value type*. If you create a new `String` value, that `String` 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 `String` value is created, and the new copy is passed or assigned, not the original version. Value types are described in . Swift's copy-by-default `String` behavior ensures that when a function or method passes you a `String` value, it's clear that you own that exact `String` 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 `Character` values for a `String` by iterating over the string with a `for`-`in` loop: ```swift for character in "Dog!🐶" { print(character) } // D // o // g // ! // 🐶 ``` The `for`-`in` loop is described in . Alternatively, you can create a stand-alone `Character` constant or variable from a single-character string literal by providing a `Character` type annotation: ```swift let exclamationMark: Character = "!" ``` `String` values can be constructed by passing an array of `Character` values as an argument to its initializer: ```swift let catCharacters: [Character] = ["C", "a", "t", "!", "🐱"] let catString = String(catCharacters) print(catString) // Prints "Cat!🐱". ``` ## Concatenating Strings and Characters `String` values can be added together (or *concatenated*) with the addition operator (`+`) to create a new `String` value: ```swift let string1 = "hello" let string2 = " there" var welcome = string1 + string2 // welcome now equals "hello there" ``` You can also append a `String` value to an existing `String` variable with the addition assignment operator (`+=`): ```swift var instruction = "look over" instruction += string2 // instruction now equals "look over there" ``` You can append a `Character` value to a `String` variable with the `String` type's `append()` method: ```swift let exclamationMark: Character = "!" welcome.append(exclamationMark) // welcome now equals "hello there!" ``` > Note: You can't append a `String` or `Character` to an existing `Character` variable, > because a `Character` 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: ```swift let badStart = """ one two """ let end = """ three """ print(badStart + end) // Prints two lines: // one // twothree let goodStart = """ one two """ print(goodStart + end) // Prints three lines: // one // two // three ``` In the code above, concatenating `badStart` with `end` produces a two-line string, which isn't the desired result. Because the last line of `badStart` doesn't end with a line break, that line gets combined with the first line of `end`. In contrast, both lines of `goodStart` end with a line break, so when it's combined with `end` the result has three lines, as expected. ## String Interpolation *String interpolation* is a way to construct a new `String` 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 (`\`): ```swift let multiplier = 3 let message = "\(multiplier) times 2.5 is \(Double(multiplier) * 2.5)" // message is "3 times 2.5 is 7.5" ``` In the example above, the value of `multiplier` is inserted into a string literal as `\(multiplier)`. This placeholder is replaced with the actual value of `multiplier` when the string interpolation is evaluated to create an actual string. The value of `multiplier` is also part of a larger expression later in the string. This expression calculates the value of `Double(multiplier) * 2.5` and inserts the result (`7.5`) into the string. In this case, the expression is written as `\(Double(multiplier) * 2.5)` 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: ```swift print(#"Write an interpolated string in Swift using \(multiplier)."#) // 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: ```swift print(#"6 times 7 is \#(6 * 7)."#) // 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 `String` and `Character` types are fully Unicode-compliant, as described in this section. ### Unicode Scalar Values Behind the scenes, Swift's native `String` type is built from *Unicode scalar values*. A Unicode scalar value is a unique 21-bit number for a character or modifier, such as `U+0061` for `LATIN SMALL LETTER A` (`"a"`), or `U+1F425` for `FRONT-FACING BABY CHICK` (`"🐥"`). 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 `LATIN SMALL LETTER A` and `FRONT-FACING BABY CHICK` in the examples above. ### Extended Grapheme Clusters Every instance of Swift's `Character` 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 `é` can be represented as the single Unicode scalar `é` (`LATIN SMALL LETTER E WITH ACUTE`, or `U+00E9`). However, the same letter can also be represented as a *pair* of scalars --- a standard letter `e` (`LATIN SMALL LETTER E`, or `U+0065`), followed by the `COMBINING ACUTE ACCENT` scalar (`U+0301`). The `COMBINING ACUTE ACCENT` scalar is graphically applied to the scalar that precedes it, turning an `e` into an `é` when it's rendered by a Unicode-aware text-rendering system. In both cases, the letter `é` is represented as a single Swift `Character` 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: ```swift let eAcute: Character = "\u{E9}" // é let combinedEAcute: Character = "\u{65}\u{301}" // e followed by ́ // eAcute is é, combinedEAcute is é ``` Extended grapheme clusters are a flexible way to represent many complex script characters as a single `Character` 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 `Character` value in Swift: ```swift let precomposed: Character = "\u{D55C}" // 한 let decomposed: Character = "\u{1112}\u{1161}\u{11AB}" // ᄒ, ᅡ, ᆫ // precomposed is 한, decomposed is 한 ``` Extended grapheme clusters enable scalars for enclosing marks (such as `COMBINING ENCLOSING CIRCLE`, or `U+20DD`) to enclose other Unicode scalars as part of a single `Character` value: ```swift let enclosedEAcute: Character = "\u{E9}\u{20DD}" // enclosedEAcute is é⃝ ``` Unicode scalars for regional indicator symbols can be combined in pairs to make a single `Character` value, such as this combination of `REGIONAL INDICATOR SYMBOL LETTER U` (`U+1F1FA`) and `REGIONAL INDICATOR SYMBOL LETTER S` (`U+1F1F8`): ```swift let regionalIndicatorForUS: Character = "\u{1F1FA}\u{1F1F8}" // regionalIndicatorForUS is 🇺🇸 ``` ## Counting Characters To retrieve a count of the `Character` values in a string, use the `count` property of the string: ```swift let unusualMenagerie = "Koala 🐨, Snail 🐌, Penguin 🐧, Dromedary 🐪" print("unusualMenagerie has \(unusualMenagerie.count) characters") // Prints "unusualMenagerie has 40 characters". ``` Note that Swift's use of extended grapheme clusters for `Character` 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 `cafe`, and then append a `COMBINING ACUTE ACCENT` (`U+0301`) to the end of the string, the resulting string will still have a character count of `4`, with a fourth character of `é`, not `e`: ```swift var word = "cafe" print("the number of characters in \(word) is \(word.count)") // Prints "the number of characters in cafe is 4". word += "\u{301}" // COMBINING ACUTE ACCENT, U+0301 print("the number of characters in \(word) is \(word.count)") // 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 `count` 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 `count` property > isn't always the same as the `length` property of > an `NSString` that contains the same characters. > The length of an `NSString` 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 `String` value has an associated *index type*, `String.Index`, which corresponds to the position of each `Character` in the string. As mentioned above, different characters can require different amounts of memory to store, so in order to determine which `Character` is at a particular position, you must iterate over each Unicode scalar from the start or end of that `String`. For this reason, Swift strings can't be indexed by integer values. Use the `startIndex` property to access the position of the first `Character` of a `String`. The `endIndex` property is the position after the last character in a `String`. As a result, the `endIndex` property isn't a valid argument to a string's subscript. If a `String` is empty, `startIndex` and `endIndex` are equal. You access the indices before and after a given index using the `index(before:)` and `index(after:)` methods of `String`. To access an index farther away from the given index, you can use the `index(_:offsetBy:)` method instead of calling one of these methods multiple times. You can use subscript syntax to access the `Character` at a particular `String` index. ```swift let greeting = "Guten Tag!" greeting[greeting.startIndex] // G greeting[greeting.index(before: greeting.endIndex)] // ! greeting[greeting.index(after: greeting.startIndex)] // u let index = greeting.index(greeting.startIndex, offsetBy: 7) greeting[index] // a ``` Attempting to access an index outside of a string's range or a `Character` at an index outside of a string's range will trigger a runtime error. ```swift greeting[greeting.endIndex] // Error greeting.index(after: greeting.endIndex) // Error ``` Use the `indices` property to access all of the indices of individual characters in a string. ```swift for index in greeting.indices { print("\(greeting[index]) ", terminator: "") } // Prints "G u t e n T a g ! ". ``` > Note: You can use the `startIndex` and `endIndex` properties > and the `index(before:)`, `index(after:)`, and `index(_:offsetBy:)` methods > on any type that conforms to the `Collection` protocol. > This includes `String`, as shown here, > as well as collection types such as `Array`, `Dictionary`, and `Set`. ### Inserting and Removing To insert a single character into a string at a specified index, use the `insert(_:at:)` method, and to insert the contents of another string at a specified index, use the `insert(contentsOf:at:)` method. ```swift var welcome = "hello" welcome.insert("!", at: welcome.endIndex) // welcome now equals "hello!" welcome.insert(contentsOf: " there", at: welcome.index(before: welcome.endIndex)) // welcome now equals "hello there!" ``` To remove a single character from a string at a specified index, use the `remove(at:)` method, and to remove a substring at a specified range, use the `removeSubrange(_:)` method: ```swift welcome.remove(at: welcome.index(before: welcome.endIndex)) // welcome now equals "hello there" let range = welcome.index(welcome.endIndex, offsetBy: -6).. welcome.remove(at: welcome.index(before: welcome.endIndex)) /> welcome now equals \"\(welcome)\" let range = welcome.index(welcome.endIndex, offsetBy: -6).. welcome.removeSubrange(range) /> welcome now equals \"\(welcome)\" > Note: You can use the `insert(_:at:)`, `insert(contentsOf:at:)`, > `remove(at:)`, and `removeSubrange(_:)` methods > on any type that conforms to the `RangeReplaceableCollection` protocol. > This includes `String`, as shown here, > as well as collection types such as `Array`, `Dictionary`, and `Set`. ## Substrings When you get a substring from a string --- for example, using a subscript or a method like `prefix(_:)` --- the result is an instance of [`Substring`](https://developer.apple.com/documentation/swift/substring), 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 `String`. For example: ```swift let greeting = "Hello, world!" let index = greeting.firstIndex(of: ",") ?? greeting.endIndex let beginning = greeting[.. let greeting = "Hello, world!" -> let index = greeting.firstIndex(of: ",") ?? greeting.endIndex -> let beginning = greeting[.. beginning is \"\(beginning)\" let newString = 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, `greeting` is a string, which means it has a region of memory where the characters that make up the string are stored. Because `beginning` is a substring of `greeting`, it reuses the memory that `greeting` uses. In contrast, `newString` is a string --- when it's created from the substring, it has its own storage. The figure below shows these relationships: ![](stringSubstring) > Note: Both `String` and `Substring` conform to the > [`StringProtocol`](https://developer.apple.com/documentation/swift/stringprotocol) protocol, > which means it's often convenient for string-manipulation functions > to accept a `StringProtocol` value. > You can call such functions with either a `String` or `Substring` 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 : ```swift let quotation = "We're a lot alike, you and I." let sameQuotation = "We're a lot alike, you and I." if quotation == sameQuotation { print("These two strings are considered equal") } // Prints "These two strings are considered equal". ``` Two `String` values (or two `Character` 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, `LATIN SMALL LETTER E WITH ACUTE` (`U+00E9`) is canonically equivalent to `LATIN SMALL LETTER E` (`U+0065`) followed by `COMBINING ACUTE ACCENT` (`U+0301`). Both of these extended grapheme clusters are valid ways to represent the character `é`, and so they're considered to be canonically equivalent: ```swift // "Voulez-vous un café?" using LATIN SMALL LETTER E WITH ACUTE let eAcuteQuestion = "Voulez-vous un caf\u{E9}?" // "Voulez-vous un café?" using LATIN SMALL LETTER E and COMBINING ACUTE ACCENT let combinedEAcuteQuestion = "Voulez-vous un caf\u{65}\u{301}?" if eAcuteQuestion == combinedEAcuteQuestion { print("These two strings are considered equal") } // Prints "These two strings are considered equal". ``` Conversely, `LATIN CAPITAL LETTER A` (`U+0041`, or `"A"`), as used in English, is *not* equivalent to `CYRILLIC CAPITAL LETTER A` (`U+0410`, or `"А"`), as used in Russian. The characters are visually similar, but don't have the same linguistic meaning: ```swift let latinCapitalLetterA: Character = "\u{41}" let cyrillicCapitalLetterA: Character = "\u{0410}" if latinCapitalLetterA != cyrillicCapit …(truncated)