Strings

Overview

Like many languages, V has built-in support for strings. Like Go, V uses UTF-8 to encode strings. All strings in V are an immutable byte array.

Strings in V are specified using single or double quotes. Both options are equivalent; however, it is recommended to use single quotes for strings that do not contain single quotes.

That is, as long as the string does not contain other single quotes, it is better to use single quotes:

println('Just string')

But if the string contains single quotes, then it is better to use double quotes to avoid having to escape the single quotes:

println("String with 'single quotes'")

vfmt will automatically convert double quotes to single quotes when possible.

Escaping in strings is supported as in C:

println('\r\n'.len) // 2

Since strings are stored in UTF-8, any characters can be used, including emoji:

println('🌎') // 🌎

Arbitrary bytes can be directly specified using \x## notation where # is a hex digit:

println('\xc0'[0]) // u8(0xc0)

Or using octal escape \### notation where # is an octal digit:

println('\141ardvark' == 'aardvark') // true

Unicode can be specified directly as \u#### where # is a hex digit and will be converted internally to its UTF-8 representation:

println('\u2605') // ★ println('\xe2\x98\x85') // ★

Since all characters in V are stored in UTF-8, the length of the string may differ from the number of visible characters in it:

s := 'hello 🌎' // emoji takes 4 bytes println(s.len) // 10

String values are immutable. You cannot mutate elements:

mut s := 'hello 🌎' s[0] = `H` // ^ error: cannot assign to s[i] since V strings are immutable // (note, that variables may be mutable but string values are always // immutable, like in Go and Java)

Note that indexing a string will produce a byte, not a rune nor another string. Indexes correspond to bytes in the string, not Unicode code points. If you want to convert the byte to a string, use the .ascii_str() method on the byte:

country := 'Netherlands' println(country[0]) // 78 println(country[0].ascii_str()) // N

String conversion

to int or other numeric types

To get an int from a string, use the .int() or .<type-name>() method:

s := '42' println(s.int()) // 42 println('100'.u8()) // 100 println('100'.i16()) // 100

All int literals are supported:

println('0xc3'.int()) // 195 println('0o10'.int()) // 8 println('0b1111_0000_1010'.int()) // 3850 println('-0b1111_0000_1010'.int()) // -3850

to f32 or f64

To get a float from a string, use the .f32() or .f64() method:

println('3.14'.f32()) // 3.14 println('3.14'.f64()) // 3.14

to bool

To get a bool from a string, use the .bool() method:

println('true'.bool()) // true println('false'.bool()) // false

to []u8

To get an array of bytes from a string, use the .bytes() method:

arr := s.bytes() println(arr.len) // 10

from []u8

To turn an array of bytes into a string, use the .bytestr() method:

s2 := arr.bytestr()

to []rune

To get an array of runes from a string, use the .runes() method:

arr := 'hello 🌎'.runes() println(arr.len) // 7

from []rune

To turn an array of runes into a string, use the .string() method:

arr := 'hello 🌎'.runes() s2 := arr.string() println(s2) // hello 🌎

For more advanced string processing and conversions, refer to the vlib/strconv module.

Raw strings

V also supports "raw" strings, which do not handle escaping and do not support string interpolation.

For raw strings, prepend string literal with r:

s := r'hello\nworld' // the `\n` will be preserved as two characters println(s) // hello\nworld

C strings

V also supports C strings, which are null-terminated arrays of bytes.

For raw strings, prepend string literal with c:

s := c'hello\nworld' println(typeof(s)) // &u8 println(s) // &104

String interpolation

Basic interpolation syntax is pretty simple – use ${ before a variable name and } after. The variable will be converted to a string and embedded into the literal:

name := 'Bob' println('Hello, ${name}!') // Hello, Bob!

It also works with fields:

println('age = ${user.age}')

And with complex expressions:

println('can register = ${user.age > 13}')

Format specifiers

To control the output format, you can use format specifiers like those used in C in printf(). Format specifiers are optional and specify the output format. The compiler takes care of the storage size, so there is no hd or llu.

To use a format specifier, follow this pattern:

${varname:[flags][width][.precision][type]}

Flags

Zero or more of the following:

  • - – left-align output within the field. The default is to right-align.
  • 0 – use 0 as the padding character instead of the default space character.

V does not currently support the use of ' or # as format flags, and V supports but doesn't need + to right-align since that's the default.

Width

Integer value describing the minimum width of total field to output.

Precision

Integer value preceded by a . will guarantee that many digits after the decimal point, if the input variable is a float.

Ignored if variable is an integer.

Type

  • f and F specify the input is a float and should be rendered as such.
  • e and E specify the input is a float and should be rendered as an exponent (partially broken).
  • g and G specify the input is a float--the renderer will use floating point notation for small values and exponent notation for large values.
  • d specifies the input is an integer and should be rendered in base-10 digits.
  • x and X require an integer and will render it as hexadecimal digits.
  • o requires an integer and will render it as octal digits.
  • b requires an integer and will render it as binary digits.
  • s requires a string (almost never used).

When a numeric type can render alphabetic characters, such as hex strings or special values like infinity, the lowercase version of the type forces lowercase alphabetic and the uppercase version forces uppercase alphabetic.

In most cases, it is best to leave the format type empty. Floats will be rendered by default as g, integers will be rendered by default as d, and s is almost always redundant. There are only three cases where specifying a type is recommended:

  • format strings are parsed at compile time, so specifying a type can help detect errors then
  • format strings default to using lowercase letters for hex digits and the e in exponents. Use an uppercase type to force the use of uppercase hex digits and an uppercase E in exponents.
  • format strings are the most convenient way to get hex, binary, or octal strings from an integer.

See Format Placeholder Specification for more information.

x := 123.4567 println('[${x:.2}]') // round to two decimal places => [123.46] println('[${x:10}]') // right-align with spaces on the left => [ 123.457] println('[${int(x):-10}]') // left-align with spaces on the right => [123 ] println('[${int(x):010}]') // pad with zeros on the left => [0000000123] println('[${int(x):b}]') // output as binary => [1111011] println('[${int(x):o}]') // output as octal => [173] println('[${int(x):X}]') // output as uppercase hex => [7B] println('[${10.0000:.2}]') // remove insignificant 0s at the end => [10] println('[${10.0000:.2f}]') // do show the 0s at the end, even though they // do not change the number => [10.00]

String operators

V defines the + and += operators for strings:

+ – used for string concatenation

name := 'Bob' bobby := name + 'by' println(bobby) // Bobby

+= – used to append to a string

mut s := 'Hello, ' s += 'World!' println(s) // Hello, World!

All operators in V must have values of the same type on both sides. You cannot concatenate an integer to a string:

age := 20 println('age = ' + age) // ^^^^^^^^^^^^^^ error: infix expr: // cannot use `int` (right expression) as `string`

To concatenate a string with a number, you must first convert the number to a string.

age := 21 println('age = ' + age.str()) // age = 21

or use string interpolation (preferred):

age := 22 println('age = ${age}') // age = 22

See all methods of string and related modules strings, strconv.

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