Primitive Type char

1.0.0 · [−]
Expand description

A character type.

The char type represents a single character. More specifically, since ‘character’ isn’t a well-defined concept in Unicode, char is a ‘Unicode scalar value’.

This documentation describes a number of methods and trait implementations on the char type. For technical reasons, there is additional, separate documentation in the std::char module as well.

Validity

A char is a ‘Unicode scalar value’, which is any ‘Unicode code point’ other than a surrogate code point. This has a fixed numerical definition: code points are in the range 0 to 0x10FFFF, inclusive. Surrogate code points, used by UTF-16, are in the range 0xD800 to 0xDFFF.

No char may be constructed, whether as a literal or at runtime, that is not a Unicode scalar value:

ⓘ
// Each of these is a compiler error
['\u{D800}', '\u{DFFF}', '\u{110000}'];
Run
ⓘ
// Panics; from_u32 returns None.
char::from_u32(0xDE01).unwrap();
Run
// Undefined behaviour
unsafe { char::from_u32_unchecked(0x110000) };
Run

USVs are also the exact set of values that may be encoded in UTF-8. Because char values are USVs and str values are valid UTF-8, it is safe to store any char in a str or read any character from a str as a char.

The gap in valid char values is understood by the compiler, so in the below example the two ranges are understood to cover the whole range of possible char values and there is no error for a non-exhaustive match.

let c: char = 'a';
match c {
    '\0' ..= '\u{D7FF}' => false,
    '\u{E000}' ..= '\u{10FFFF}' => true,
};
Run

All USVs are valid char values, but not all of them represent a real character. Many USVs are not currently assigned to a character, but may be in the future (“reserved”); some will never be a character (“noncharacters”); and some may be given different meanings by different users (“private use”).

Representation

char is always four bytes in size. This is a different representation than a given character would have as part of a String. For example:

let v = vec!['h', 'e', 'l', 'l', 'o'];

// five elements times four bytes for each element
assert_eq!(20, v.len() * std::mem::size_of::<char>());

let s = String::from("hello");

// five elements times one byte per element
assert_eq!(5, s.len() * std::mem::size_of::<u8>());
Run

As always, remember that a human intuition for ‘character’ might not map to Unicode’s definitions. For example, despite looking similar, the ‘é’ character is one Unicode code point while ‘é’ is two Unicode code points:

let mut chars = "é".chars();
// U+00e9: 'latin small letter e with acute'
assert_eq!(Some('\u{00e9}'), chars.next());
assert_eq!(None, chars.next());

let mut chars = "é".chars();
// U+0065: 'latin small letter e'
assert_eq!(Some('\u{0065}'), chars.next());
// U+0301: 'combining acute accent'
assert_eq!(Some('\u{0301}'), chars.next());
assert_eq!(None, chars.next());
Run

This means that the contents of the first string above will fit into a char while the contents of the second string will not. Trying to create a char literal with the contents of the second string gives an error:

error: character literal may only contain one codepoint: 'é'
let c = 'é';
        ^^^

Another implication of the 4-byte fixed size of a char is that per-char processing can end up using a lot more memory:

let s = String::from("love: ❤️");
let v: Vec<char> = s.chars().collect();

assert_eq!(12, std::mem::size_of_val(&s[..]));
assert_eq!(32, std::mem::size_of_val(&v[..]));
Run

Implementations

The highest valid code point a char can have, '\u{10FFFF}'.

Examples
let c: char = something_which_returns_char();
assert!(c <= char::MAX);

let value_at_max = char::MAX as u32;
assert_eq!(char::from_u32(value_at_max), Some('\u{10FFFF}'));
assert_eq!(char::from_u32(value_at_max + 1), None);
Run

U+FFFD REPLACEMENT CHARACTER (�) is used in Unicode to represent a decoding error.

It can occur, for example, when giving ill-formed UTF-8 bytes to String::from_utf8_lossy.

The version of Unicode that the Unicode parts of char and str methods are based on.

New versions of Unicode are released regularly and subsequently all methods in the standard library depending on Unicode are updated. Therefore the behavior of some char and str methods and the value of this constant changes over time. This is not considered to be a breaking change.

The version numbering scheme is explained in Unicode 11.0 or later, Section 3.1 Versions of the Unicode Standard.

Creates an iterator over the UTF-16 encoded code points in iter, returning unpaired surrogates as Errs.

Examples

Basic usage:

use std::char::decode_utf16;

// 𝄞mus<invalid>ic<invalid>
let v = [
    0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0xDD1E, 0x0069, 0x0063, 0xD834,
];

assert_eq!(
    decode_utf16(v)
        .map(|r| r.map_err(|e| e.unpaired_surrogate()))
        .collect::<Vec<_>>(),
    vec![
        Ok('𝄞'),
        Ok('m'), Ok('u'), Ok('s'),
        Err(0xDD1E),
        Ok('i'), Ok('c'),
        Err(0xD834)
    ]
);
Run

A lossy decoder can be obtained by replacing Err results with the replacement character:

use std::char::{decode_utf16, REPLACEMENT_CHARACTER};

// 𝄞mus<invalid>ic<invalid>
let v = [
    0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0xDD1E, 0x0069, 0x0063, 0xD834,
];

assert_eq!(
    decode_utf16(v)
       .map(|r| r.unwrap_or(REPLACEMENT_CHARACTER))
       .collect::<String>(),
    "𝄞mus�ic�"
);
Run

Converts a u32 to a char.

Note that all chars are valid u32s, and can be cast to one with as:

let c = '💯';
let i = c as u32;

assert_eq!(128175, i);
Run

However, the reverse is not true: not all valid u32s are valid chars. from_u32() will return None if the input is not a valid value for a char.

For an unsafe version of this function which ignores these checks, see from_u32_unchecked.

Examples

Basic usage:

use std::char;

let c = char::from_u32(0x2764);

assert_eq!(Some('❤'), c);
Run

Returning None when the input is not a valid char:

use std::char;

let c = char::from_u32(0x110000);

assert_eq!(None, c);
Run

Converts a u32 to a char, ignoring validity.

Note that all chars are valid u32s, and can be cast to one with as:

let c = '💯';
let i = c as u32;

assert_eq!(128175, i);
Run

However, the reverse is not true: not all valid u32s are valid chars. from_u32_unchecked() will ignore this, and blindly cast to char, possibly creating an invalid one.

Safety

This function is unsafe, as it may construct invalid char values.

For a safe version of this function, see the from_u32 function.

Examples

Basic usage:

use std::char;

let c = unsafe { char::from_u32_unchecked(0x2764) };

assert_eq!('❤', c);
Run

Converts a digit in the given radix to a char.

A ‘radix’ here is sometimes also called a ‘base’. A radix of two indicates a binary number, a radix of ten, decimal, and a radix of sixteen, hexadecimal, to give some common values. Arbitrary radices are supported.

from_digit() will return None if the input is not a digit in the given radix.

Panics

Panics if given a radix larger than 36.

Examples

Basic usage:

use std::char;

let c = char::from_digit(4, 10);

assert_eq!(Some('4'), c);

// Decimal 11 is a single digit in base 16
let c = char::from_digit(11, 16);

assert_eq!(Some('b'), c);
Run

Returning None when the input is not a digit:

use std::char;

let c = char::from_digit(20, 10);

assert_eq!(None, c);
Run

Passing a large radix, causing a panic:

ⓘ
use std::char;

// this panics
let _c = char::from_digit(1, 37);
Run

Checks if a char is a digit in the given radix.

A ‘radix’ here is sometimes also called a ‘base’. A radix of two indicates a binary number, a radix of ten, decimal, and a radix of sixteen, hexadecimal, to give some common values. Arbitrary radices are supported.

Compared to is_numeric(), this function only recognizes the characters 0-9, a-z and A-Z.

‘Digit’ is defined to be only the following characters:

  • 0-9
  • a-z
  • A-Z

For a more comprehensive understanding of ‘digit’, see is_numeric().

Panics

Panics if given a radix larger than 36.

Examples

Basic usage:

assert!('1'.is_digit(10));
assert!('f'.is_digit(16));
assert!(!'f'.is_digit(10));
Run

Passing a large radix, causing a panic:

ⓘ
// this panics
'1'.is_digit(37);
Run

Converts a char to a digit in the given radix.

A ‘radix’ here is sometimes also called a ‘base’. A radix of two indicates a binary number, a radix of ten, decimal, and a radix of sixteen, hexadecimal, to give some common values. Arbitrary radices are supported.

‘Digit’ is defined to be only the following characters:

  • 0-9
  • a-z
  • A-Z
Errors

Returns None if the char does not refer to a digit in the given radix.

Panics

Panics if given a radix larger than 36.

Examples

Basic usage:

assert_eq!('1'.to_digit(10), Some(1));
assert_eq!('f'.to_digit(16), Some(15));
Run

Passing a non-digit results in failure:

assert_eq!('f'.to_digit(10), None);
assert_eq!('z'.to_digit(16), None);
Run

Passing a large radix, causing a panic:

ⓘ
// this panics
let _ = '1'.to_digit(37);
Run

Returns an iterator that yields the hexadecimal Unicode escape of a character as chars.

This will escape characters with the Rust syntax of the form \u{NNNNNN} where NNNNNN is a hexadecimal representation.

Examples

As an iterator:

for c in '❤'.escape_unicode() {
    print!("{c}");
}
println!();
Run

Using println! directly:

println!("{}", '❤'.escape_unicode());
Run

Both are equivalent to:

println!("\\u{{2764}}");
Run

Using to_string:

assert_eq!('❤'.escape_unicode().to_string(), "\\u{2764}");
Run

Returns an iterator that yields the literal escape code of a character as chars.

This will escape the characters similar to the Debug implementations of str or char.

Examples

As an iterator:

for c in '\n'.escape_debug() {
    print!("{c}");
}
println!();
Run

Using println! directly:

println!("{}", '\n'.escape_debug());
Run

Both are equivalent to:

println!("\\n");
Run

Using to_string:

assert_eq!('\n'.escape_debug().to_string(), "\\n");
Run

Returns an iterator that yields the literal escape code of a character as chars.

The default is chosen with a bias toward producing literals that are legal in a variety of languages, including C++11 and similar C-family languages. The exact rules are:

  • Tab is escaped as \t.
  • Carriage return is escaped as \r.
  • Line feed is escaped as \n.
  • Single quote is escaped as \'.
  • Double quote is escaped as \".
  • Backslash is escaped as \\.
  • Any character in the ‘printable ASCII’ range 0x20 .. 0x7e inclusive is not escaped.
  • All other characters are given hexadecimal Unicode escapes; see escape_unicode.
Examples

As an iterator:

for c in '"'.escape_default() {
    print!("{c}");
}
println!();
Run

Using println! directly:

println!("{}", '"'.escape_default());
Run

Both are equivalent to:

println!("\\\"");
Run

Using to_string:

assert_eq!('"'.escape_default().to_string(), "\\\"");
Run

Returns the number of bytes this char would need if encoded in UTF-8.

That number of bytes is always between 1 and 4, inclusive.

Examples

Basic usage:

let len = 'A'.len_utf8();
assert_eq!(len, 1);

let len = 'ß'.len_utf8();
assert_eq!(len, 2);

let len = 'ℝ'.len_utf8();
assert_eq!(len, 3);

let len = '💣'.len_utf8();
assert_eq!(len, 4);
Run

The &str type guarantees that its contents are UTF-8, and so we can compare the length it would take if each code point was represented as a char vs in the &str itself:

// as chars
let eastern = '東';
let capital = '京';

// both can be represented as three bytes
assert_eq!(3, eastern.len_utf8());
assert_eq!(3, capital.len_utf8());

// as a &str, these two are encoded in UTF-8
let tokyo = "東京";

let len = eastern.len_utf8() + capital.len_utf8();

// we can see that they take six bytes total...
assert_eq!(6, tokyo.len());

// ... just like the &str
assert_eq!(len, tokyo.len());
Run

Returns the number of 16-bit code units this char would need if encoded in UTF-16.

See the documentation for len_utf8() for more explanation of this concept. This function is a mirror, but for UTF-16 instead of UTF-8.

Examples

Basic usage:

let n = 'ß'.len_utf16();
assert_eq!(n, 1);

let len = '💣'.len_utf16();
assert_eq!(len, 2);
Run

Encodes this character as UTF-8 into the provided byte buffer, and then returns the subslice of the buffer that contains the encoded character.

Panics

Panics if the buffer is not large enough. A buffer of length four is large enough to encode any char.

Examples

In both of these examples, ‘ß’ takes two bytes to encode.

let mut b = [0; 2];

let result = 'ß'.encode_utf8(&mut b);

assert_eq!(result, "ß");

assert_eq!(result.len(), 2);
Run

A buffer that’s too small:

ⓘ
let mut b = [0; 1];

// this panics
'ß'.encode_utf8(&mut b);
Run

Encodes this character as UTF-16 into the provided u16 buffer, and then returns the subslice of the buffer that contains the encoded character.

Panics

Panics if the buffer is not large enough. A buffer of length 2 is large enough to encode any char.

Examples

In both of these examples, ‘𝕊’ takes two u16s to encode.

let mut b = [0; 2];

let result = '𝕊'.encode_utf16(&mut b);

assert_eq!(result.len(), 2);
Run

A buffer that’s too small:

ⓘ
let mut b = [0; 1];

// this panics
'𝕊'.encode_utf16(&mut b);
Run

Returns true if this char has the Alphabetic property.

Alphabetic is described in Chapter 4 (Character Properties) of the Unicode Standard and specified in the Unicode Character Database DerivedCoreProperties.txt.

Examples

Basic usage:

assert!('a'.is_alphabetic());
assert!('京'.is_alphabetic());

let c = '💝';
// love is many things, but it is not alphabetic
assert!(!c.is_alphabetic());
Run

Returns true if this char has the Lowercase property.

Lowercase is described in Chapter 4 (Character Properties) of the Unicode Standard and specified in the Unicode Character Database DerivedCoreProperties.txt.

Examples

Basic usage:

assert!('a'.is_lowercase());
assert!('δ'.is_lowercase());
assert!(!'A'.is_lowercase());
assert!(!'Δ'.is_lowercase());

// The various Chinese scripts and punctuation do not have case, and so:
assert!(!'中'.is_lowercase());
assert!(!' '.is_lowercase());
Run

Returns true if this char has the Uppercase property.

Uppercase is described in Chapter 4 (Character Properties) of the Unicode Standard and specified in the Unicode Character Database DerivedCoreProperties.txt.

Examples

Basic usage:

assert!(!'a'.is_uppercase());
assert!(!'δ'.is_uppercase());
assert!('A'.is_uppercase());
assert!('Δ'.is_uppercase());

// The various Chinese scripts and punctuation do not have case, and so:
assert!(!'中'.is_uppercase());
assert!(!' '.is_uppercase());
Run

Returns true if this char has the White_Space property.

White_Space is specified in the Unicode Character Database PropList.txt.

Examples

Basic usage:

assert!(' '.is_whitespace());

// line break
assert!('\n'.is_whitespace());

// a non-breaking space
assert!('\u{A0}'.is_whitespace());

assert!(!'越'.is_whitespace());
Run

Returns true if this char satisfies either is_alphabetic() or is_numeric().

Examples

Basic usage:

assert!('٣'.is_alphanumeric());
assert!('7'.is_alphanumeric());
assert!('৬'.is_alphanumeric());
assert!('¾'.is_alphanumeric());
assert!('①'.is_alphanumeric());
assert!('K'.is_alphanumeric());
assert!('و'.is_alphanumeric());
assert!('藏'.is_alphanumeric());
Run

Returns true if this char has the general category for control codes.

Control codes (code points with the general category of Cc) are described in Chapter 4 (Character Properties) of the Unicode Standard and specified in the Unicode Character Database UnicodeData.txt.

Examples

Basic usage:

// U+009C, STRING TERMINATOR
assert!('œ'.is_control());
assert!(!'q'.is_control());
Run

Returns true if this char has one of the general categories for numbers.

The general categories for numbers (Nd for decimal digits, Nl for letter-like numeric characters, and No for other numeric characters) are specified in the Unicode Character Database UnicodeData.txt. Note that this means ideographic numbers like ‘三’ are considered alphabetic, not numeric. Please consider to use is_ascii_digit or is_digit.

This method doesn’t cover everything that could be considered a number, e.g. ideographic numbers like ‘三’. If you want everything including characters with overlapping purposes then you might want to use a unicode or language-processing library that exposes the appropriate character properties instead of looking at the unicode categories.

If you want to parse ASCII decimal digits (0-9) or ASCII base-N, use is_ascii_digit or is_digit instead.

Examples

Basic usage:

assert!('٣'.is_numeric());
assert!('7'.is_numeric());
assert!('৬'.is_numeric());
assert!('¾'.is_numeric());
assert!('①'.is_numeric());
assert!(!'K'.is_numeric());
assert!(!'و'.is_numeric());
assert!(!'藏'.is_numeric());
assert!(!'三'.is_numeric());
Run

Returns an iterator that yields the lowercase mapping of this char as one or more chars.

If this char does not have a lowercase mapping, the iterator yields the same char.

If this char has a one-to-one lowercase mapping given by the Unicode Character Database UnicodeData.txt, the iterator yields that char.

If this char requires special considerations (e.g. multiple chars) the iterator yields the char(s) given by SpecialCasing.txt.

This operation performs an unconditional mapping without tailoring. That is, the conversion is independent of context and language.

In the Unicode Standard, Chapter 4 (Character Properties) discusses case mapping in general and Chapter 3 (Conformance) discusses the default algorithm for case conversion.

Examples

As an iterator:

for c in 'İ'.to_lowercase() {
    print!("{c}");
}
println!();
Run

Using println! directly:

println!("{}", 'İ'.to_lowercase());
Run

Both are equivalent to:

println!("i\u{307}");
Run

Using to_string:

assert_eq!('C'.to_lowercase().to_string(), "c");

// Sometimes the result is more than one character:
assert_eq!('İ'.to_lowercase().to_string(), "i\u{307}");

// Characters that do not have both uppercase and lowercase
// convert into themselves.
assert_eq!('山'.to_lowercase().to_string(), "山");
Run

Returns an iterator that yields the uppercase mapping of this char as one or more chars.

If this char does not have an uppercase mapping, the iterator yields the same char.

If this char has a one-to-one uppercase mapping given by the Unicode Character Database UnicodeData.txt, the iterator yields that char.

If this char requires special considerations (e.g. multiple chars) the iterator yields the char(s) given by SpecialCasing.txt.

This operation performs an unconditional mapping without tailoring. That is, the conversion is independent of context and language.

In the Unicode Standard, Chapter 4 (Character Properties) discusses case mapping in general and Chapter 3 (Conformance) discusses the default algorithm for case conversion.

Examples

As an iterator:

for c in 'ß'.to_uppercase() {
    print!("{c}");
}
println!();
Run

Using println! directly:

println!("{}", 'ß'.to_uppercase());
Run

Both are equivalent to:

println!("SS");
Run

Using to_string:

assert_eq!('c'.to_uppercase().to_string(), "C");

// Sometimes the result is more than one character:
assert_eq!('ß'.to_uppercase().to_string(), "SS");

// Characters that do not have both uppercase and lowercase
// convert into themselves.
assert_eq!('山'.to_uppercase().to_string(), "山");
Run
Note on locale

In Turkish, the equivalent of ‘i’ in Latin has five forms instead of two:

  • ‘Dotless’: I / ı, sometimes written ï
  • ‘Dotted’: İ / i

Note that the lowercase dotted ‘i’ is the same as the Latin. Therefore:

let upper_i = 'i'.to_uppercase().to_string();
Run

The value of upper_i here relies on the language of the text: if we’re in en-US, it should be "I", but if we’re in tr_TR, it should be "İ". to_uppercase() does not take this into account, and so:

let upper_i = 'i'.to_uppercase().to_string();

assert_eq!(upper_i, "I");
Run

holds across languages.

Checks if the value is within the ASCII range.

Examples
let ascii = 'a';
let non_ascii = '❤';

assert!(ascii.is_ascii());
assert!(!non_ascii.is_ascii());
Run

Makes a copy of the value in its ASCII upper case equivalent.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To uppercase the value in-place, use make_ascii_uppercase().

To uppercase ASCII characters in addition to non-ASCII characters, use to_uppercase().

Examples
let ascii = 'a';
let non_ascii = '❤';

assert_eq!('A', ascii.to_ascii_uppercase());
assert_eq!('❤', non_ascii.to_ascii_uppercase());
Run

Makes a copy of the value in its ASCII lower case equivalent.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To lowercase the value in-place, use make_ascii_lowercase().

To lowercase ASCII characters in addition to non-ASCII characters, use to_lowercase().

Examples
let ascii = 'A';
let non_ascii = '❤';

assert_eq!('a', ascii.to_ascii_lowercase());
assert_eq!('❤', non_ascii.to_ascii_lowercase());
Run

Checks that two values are an ASCII case-insensitive match.

Equivalent to to_ascii_lowercase(a) == to_ascii_lowercase(b).

Examples
let upper_a = 'A';
let lower_a = 'a';
let lower_z = 'z';

assert!(upper_a.eq_ignore_ascii_case(&lower_a));
assert!(upper_a.eq_ignore_ascii_case(&upper_a));
assert!(!upper_a.eq_ignore_ascii_case(&lower_z));
Run

Converts this type to its ASCII upper case equivalent in-place.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To return a new uppercased value without modifying the existing one, use to_ascii_uppercase().

Examples
let mut ascii = 'a';

ascii.make_ascii_uppercase();

assert_eq!('A', ascii);
Run

Converts this type to its ASCII lower case equivalent in-place.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To return a new lowercased value without modifying the existing one, use to_ascii_lowercase().

Examples
let mut ascii = 'A';

ascii.make_ascii_lowercase();

assert_eq!('a', ascii);
Run

Checks if the value is an ASCII alphabetic character:

  • U+0041 ‘A’ ..= U+005A ‘Z’, or
  • U+0061 ‘a’ ..= U+007A ‘z’.
Examples
let uppercase_a = 'A';
let uppercase_g = 'G';
let a = 'a';
let g = 'g';
let zero = '0';
let percent = '%';
let space = ' ';
let lf = '\n';
let esc = '\x1b';

assert!(uppercase_a.is_ascii_alphabetic());
assert!(uppercase_g.is_ascii_alphabetic());
assert!(a.is_ascii_alphabetic());
assert!(g.is_ascii_alphabetic());
assert!(!zero.is_ascii_alphabetic());
assert!(!percent.is_ascii_alphabetic());
assert!(!space.is_ascii_alphabetic());
assert!(!lf.is_ascii_alphabetic());
assert!(!esc.is_ascii_alphabetic());
Run

Checks if the value is an ASCII uppercase character: U+0041 ‘A’ ..= U+005A ‘Z’.

Examples
let uppercase_a = 'A';
let uppercase_g = 'G';
let a = 'a';
let g = 'g';
let zero = '0';
let percent = '%';
let space = ' ';
let lf = '\n';
let esc = '\x1b';

assert!(uppercase_a.is_ascii_uppercase());
assert!(uppercase_g.is_ascii_uppercase());
assert!(!a.is_ascii_uppercase());
assert!(!g.is_ascii_uppercase());
assert!(!zero.is_ascii_uppercase());
assert!(!percent.is_ascii_uppercase());
assert!(!space.is_ascii_uppercase());
assert!(!lf.is_ascii_uppercase());
assert!(!esc.is_ascii_uppercase());
Run

Checks if the value is an ASCII lowercase character: U+0061 ‘a’ ..= U+007A ‘z’.

Examples
let uppercase_a = 'A';
let uppercase_g = 'G';
let a = 'a';
let g = 'g';
let zero = '0';
let percent = '%';
let space = ' ';
let lf = '\n';
let esc = '\x1b';

assert!(!uppercase_a.is_ascii_lowercase());
assert!(!uppercase_g.is_ascii_lowercase());
assert!(a.is_ascii_lowercase());
assert!(g.is_ascii_lowercase());
assert!(!zero.is_ascii_lowercase());
assert!(!percent.is_ascii_lowercase());
assert!(!space.is_ascii_lowercase());
assert!(!lf.is_ascii_lowercase());
assert!(!esc.is_ascii_lowercase());
Run

Checks if the value is an ASCII alphanumeric character:

  • U+0041 ‘A’ ..= U+005A ‘Z’, or
  • U+0061 ‘a’ ..= U+007A ‘z’, or
  • U+0030 ‘0’ ..= U+0039 ‘9’.
Examples
let uppercase_a = 'A';
let uppercase_g = 'G';
let a = 'a';
let g = 'g';
let zero = '0';
let percent = '%';
let space = ' ';
let lf = '\n';
let esc = '\x1b';

assert!(uppercase_a.is_ascii_alphanumeric());
assert!(uppercase_g.is_ascii_alphanumeric());
assert!(a.is_ascii_alphanumeric());
assert!(g.is_ascii_alphanumeric());
assert!(zero.is_ascii_alphanumeric());
assert!(!percent.is_ascii_alphanumeric());
assert!(!space.is_ascii_alphanumeric());
assert!(!lf.is_ascii_alphanumeric());
assert!(!esc.is_ascii_alphanumeric());
Run

Checks if the value is an ASCII decimal digit: U+0030 ‘0’ ..= U+0039 ‘9’.

Examples
let uppercase_a = 'A';
let uppercase_g = 'G';
let a = 'a';
let g = 'g';
let zero = '0';
let percent = '%';
let space = ' ';
let lf = '\n';
let esc = '\x1b';

assert!(!uppercase_a.is_ascii_digit());
assert!(!uppercase_g.is_ascii_digit());
assert!(!a.is_ascii_digit());
assert!(!g.is_ascii_digit());
assert!(zero.is_ascii_digit());
assert!(!percent.is_ascii_digit());
assert!(!space.is_ascii_digit());
assert!(!lf.is_ascii_digit());
assert!(!esc.is_ascii_digit());
Run

Checks if the value is an ASCII hexadecimal digit:

  • U+0030 ‘0’ ..= U+0039 ‘9’, or
  • U+0041 ‘A’ ..= U+0046 ‘F’, or
  • U+0061 ‘a’ ..= U+0066 ‘f’.
Examples
let uppercase_a = 'A';
let uppercase_g = 'G';
let a = 'a';
let g = 'g';
let zero = '0';
let percent = '%';
let space = ' ';
let lf = '\n';
let esc = '\x1b';

assert!(uppercase_a.is_ascii_hexdigit());
assert!(!uppercase_g.is_ascii_hexdigit());
assert!(a.is_ascii_hexdigit());
assert!(!g.is_ascii_hexdigit());
assert!(zero.is_ascii_hexdigit());
assert!(!percent.is_ascii_hexdigit());
assert!(!space.is_ascii_hexdigit());
assert!(!lf.is_ascii_hexdigit());
assert!(!esc.is_ascii_hexdigit());
Run

Checks if the value is an ASCII punctuation character:

  • U+0021 ..= U+002F ! " # $ % & ' ( ) * + , - . /, or
  • U+003A ..= U+0040 : ; < = > ? @, or
  • U+005B ..= U+0060 [ \ ] ^ _ ` , or
  • U+007B ..= U+007E { | } ~
Examples
let uppercase_a = 'A';
let uppercase_g = 'G';
let a = 'a';
let g = 'g';
let zero = '0';
let percent = '%';
let space = ' ';
let lf = '\n';
let esc = '\x1b';

assert!(!uppercase_a.is_ascii_punctuation());
assert!(!uppercase_g.is_ascii_punctuation());
assert!(!a.is_ascii_punctuation());
assert!(!g.is_ascii_punctuation());
assert!(!zero.is_ascii_punctuation());
assert!(percent.is_ascii_punctuation());
assert!(!space.is_ascii_punctuation());
assert!(!lf.is_ascii_punctuation());
assert!(!esc.is_ascii_punctuation());
Run

Checks if the value is an ASCII graphic character: U+0021 ‘!’ ..= U+007E ‘~’.

Examples
let uppercase_a = 'A';
let uppercase_g = 'G';
let a = 'a';
let g = 'g';
let zero = '0';
let percent = '%';
let space = ' ';
let lf = '\n';
let esc = '\x1b';

assert!(uppercase_a.is_ascii_graphic());
assert!(uppercase_g.is_ascii_graphic());
assert!(a.is_ascii_graphic());
assert!(g.is_ascii_graphic());
assert!(zero.is_ascii_graphic());
assert!(percent.is_ascii_graphic());
assert!(!space.is_ascii_graphic());
assert!(!lf.is_ascii_graphic());
assert!(!esc.is_ascii_graphic());
Run

Checks if the value is an ASCII whitespace character: U+0020 SPACE, U+0009 HORIZONTAL TAB, U+000A LINE FEED, U+000C FORM FEED, or U+000D CARRIAGE RETURN.

Rust uses the WhatWG Infra Standard’s definition of ASCII whitespace. There are several other definitions in wide use. For instance, the POSIX locale includes U+000B VERTICAL TAB as well as all the above characters, but—from the very same specification—the default rule for “field splitting” in the Bourne shell considers only SPACE, HORIZONTAL TAB, and LINE FEED as whitespace.

If you are writing a program that will process an existing file format, check what that format’s definition of whitespace is before using this function.

Examples
let uppercase_a = 'A';
let uppercase_g = 'G';
let a = 'a';
let g = 'g';
let zero = '0';
let percent = '%';
let space = ' ';
let lf = '\n';
let esc = '\x1b';

assert!(!uppercase_a.is_ascii_whitespace());
assert!(!uppercase_g.is_ascii_whitespace());
assert!(!a.is_ascii_whitespace());
assert!(!g.is_ascii_whitespace());
assert!(!zero.is_ascii_whitespace());
assert!(!percent.is_ascii_whitespace());
assert!(space.is_ascii_whitespace());
assert!(lf.is_ascii_whitespace());
assert!(!esc.is_ascii_whitespace());
Run

Checks if the value is an ASCII control character: U+0000 NUL ..= U+001F UNIT SEPARATOR, or U+007F DELETE. Note that most ASCII whitespace characters are control characters, but SPACE is not.

Examples
let uppercase_a = 'A';
let uppercase_g = 'G';
let a = 'a';
let g = 'g';
let zero = '0';
let percent = '%';
let space = ' ';
let lf = '\n';
let esc = '\x1b';

assert!(!uppercase_a.is_ascii_control());
assert!(!uppercase_g.is_ascii_control());
assert!(!a.is_ascii_control());
assert!(!g.is_ascii_control());
assert!(!zero.is_ascii_control());
assert!(!percent.is_ascii_control());
assert!(!space.is_ascii_control());
assert!(lf.is_ascii_control());
assert!(esc.is_ascii_control());
Run

Trait Implementations

👎 Deprecated since 1.26.0:

use inherent methods instead

Container type for copied ASCII characters.

👎 Deprecated since 1.26.0:

use inherent methods instead

Checks if the value is within the ASCII range. Read more

👎 Deprecated since 1.26.0:

use inherent methods instead

Makes a copy of the value in its ASCII upper case equivalent. Read more

👎 Deprecated since 1.26.0:

use inherent methods instead

Makes a copy of the value in its ASCII lower case equivalent. Read more

👎 Deprecated since 1.26.0:

use inherent methods instead

Checks that two values are an ASCII case-insensitive match. Read more

👎 Deprecated since 1.26.0:

use inherent methods instead

Converts this type to its ASCII upper case equivalent in-place. Read more

👎 Deprecated since 1.26.0:

use inherent methods instead

Converts this type to its ASCII lower case equivalent in-place. Read more

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

Returns the default value of \x00

Formats the value using the given formatter. Read more

Extends a collection with the contents of an iterator. Read more

🔬 This is a nightly-only experimental API. (extend_one #72631)

Extends a collection with exactly one element.

🔬 This is a nightly-only experimental API. (extend_one #72631)

Reserves capacity in a collection for the given number of additional elements. Read more

Extends a collection with the contents of an iterator. Read more

🔬 This is a nightly-only experimental API. (extend_one #72631)

Extends a collection with exactly one element.

🔬 This is a nightly-only experimental API. (extend_one #72631)

Reserves capacity in a collection for the given number of additional elements. Read more

Allocates an owned String from a single character.

Example
let c: char = 'a';
let s: String = String::from(c);
assert_eq!("a", &s[..]);
Run

Converts a char into a u128.

Examples
use std::mem;

let c = '⚙';
let u = u128::from(c);
assert!(16 == mem::size_of_val(&u))
Run

Converts a char into a u32.

Examples
use std::mem;

let c = 'c';
let u = u32::from(c);
assert!(4 == mem::size_of_val(&u))
Run

Converts a char into a u64.

Examples
use std::mem;

let c = '👤';
let u = u64::from(c);
assert!(8 == mem::size_of_val(&u))
Run

Maps a byte in 0x00..=0xFF to a char whose code point has the same value, in U+0000..=U+00FF.

Unicode is designed such that this effectively decodes bytes with the character encoding that IANA calls ISO-8859-1. This encoding is compatible with ASCII.

Note that this is different from ISO/IEC 8859-1 a.k.a. ISO 8859-1 (with one less hyphen), which leaves some “blanks”, byte values that are not assigned to any character. ISO-8859-1 (the IANA one) assigns them to the C0 and C1 control codes.

Note that this is also different from Windows-1252 a.k.a. code page 1252, which is a superset ISO/IEC 8859-1 that assigns some (not all!) blanks to punctuation and various Latin characters.

To confuse things further, on the Web ascii, iso-8859-1, and windows-1252 are all aliases for a superset of Windows-1252 that fills the remaining blanks with corresponding C0 and C1 control codes.

Converts a u8 into a char.

Examples
use std::mem;

let u = 32 as u8;
let c = char::from(u);
assert!(4 == mem::size_of_val(&c))
Run

Creates a value from an iterator. Read more

Creates a value from an iterator. Read more

Creates a value from an iterator. Read more

The associated error which can be returned from parsing.

Parses a string s to return a value of this type. Read more

Feeds this value into the given Hasher. Read more

Feeds a slice of this type into the given Hasher. Read more

This method returns an Ordering between self and other. Read more

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

Restrict a value to a certain interval. Read more

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method returns an ordering between self and other values if one exists. Read more

This method tests less than (for self and other) and is used by the < operator. Read more

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

This method tests greater than (for self and other) and is used by the > operator. Read more

Searches for chars that are equal to a given char.

Examples

assert_eq!("Hello world".find('o'), Some(4));
Run
🔬 This is a nightly-only experimental API. (pattern #27721)

Associated searcher for this pattern

🔬 This is a nightly-only experimental API. (pattern #27721)

Constructs the associated searcher from self and the haystack to search in. Read more

🔬 This is a nightly-only experimental API. (pattern #27721)

Checks whether the pattern matches anywhere in the haystack

🔬 This is a nightly-only experimental API. (pattern #27721)

Checks whether the pattern matches at the front of the haystack

🔬 This is a nightly-only experimental API. (pattern #27721)

Removes the pattern from the front of haystack, if it matches.

🔬 This is a nightly-only experimental API. (pattern #27721)

Checks whether the pattern matches at the back of the haystack

🔬 This is a nightly-only experimental API. (pattern #27721)

Removes the pattern from the back of haystack, if it matches.

🔬 This is a nightly-only experimental API. (step_trait #42168)

Returns the number of successor steps required to get from start to end. Read more

🔬 This is a nightly-only experimental API. (step_trait #42168)

Returns the value that would be obtained by taking the successor of self count times. Read more

🔬 This is a nightly-only experimental API. (step_trait #42168)

Returns the value that would be obtained by taking the predecessor of self count times. Read more

🔬 This is a nightly-only experimental API. (step_trait #42168)

Returns the value that would be obtained by taking the successor of self count times. Read more

🔬 This is a nightly-only experimental API. (step_trait #42168)

Returns the value that would be obtained by taking the predecessor of self count times. Read more

🔬 This is a nightly-only experimental API. (step_trait #42168)

Returns the value that would be obtained by taking the successor of self count times. Read more

🔬 This is a nightly-only experimental API. (step_trait #42168)

Returns the value that would be obtained by taking the predecessor of self count times. Read more

Converts the given value to a String. Read more

Map char with code point in U+0000..=U+00FF to byte in 0x00..=0xFF with same value, failing if the code point is greater than U+00FF.

See impl From<u8> for char for details on the encoding.

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

Uses borrowed data to replace owned data, usually by cloning. Read more

Converts the given value to a String. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.