Struct heapless::String[−][src]

pub struct String<const N: usize> { /* fields omitted */ }

Expand description

A fixed capacity String

Implementations

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impl<const N: usize> String<N>

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pub const fn new() -> Self

Constructs a new, empty String with a fixed capacity of N

Examples

Basic usage:

use heapless::String;

// allocate the string on the stack
let mut s: String<4> = String::new();

// allocate the string in a static variable
static mut S: String<4> = String::new();

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pub fn into_bytes(self) -> Vec<u8, N>

Converts a String into a byte vector.

This consumes the String, so we do not need to copy its contents.

Examples

Basic usage:

use heapless::String;

let s: String<4> = String::from("ab");
let b = s.into_bytes();
assert!(b.len() == 2);

assert_eq!(&['a' as u8, 'b' as u8], &b[..]);

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pub fn as_str(&self) -> &str

Extracts a string slice containing the entire string.

Examples

Basic usage:

use heapless::String;

let mut s: String<4> = String::from("ab");
assert!(s.as_str() == "ab");

let _s = s.as_str();
// s.push('c'); // <- cannot borrow `s` as mutable because it is also borrowed as immutable

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pub fn as_mut_str(&mut self) -> &mut str

Converts a String into a mutable string slice.

Examples

Basic usage:

use heapless::String;

let mut s: String<4> = String::from("ab");
let s = s.as_mut_str();
s.make_ascii_uppercase();

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pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8, N>

Returns a mutable reference to the contents of this String.

Safety

This function is unsafe because it does not check that the bytes passed to it are valid UTF-8. If this constraint is violated, it may cause memory unsafety issues with future users of the String, as the rest of the library assumes that Strings are valid UTF-8.

Examples

Basic usage:

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

unsafe {
    let vec = s.as_mut_vec();
    assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);

    vec.reverse();
}
assert_eq!(s, "olleh");

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pub fn push_str(&mut self, string: &str) -> Result<(), ()>

Appends a given string slice onto the end of this String.

Examples

Basic usage:

use heapless::String;

let mut s: String<8> = String::from("foo");

assert!(s.push_str("bar").is_ok());

assert_eq!("foobar", s);

assert!(s.push_str("tender").is_err());

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pub fn capacity(&self) -> usize

Returns the maximum number of elements the String can hold

Examples

Basic usage:

use heapless::String;

let mut s: String<4> = String::new();
assert!(s.capacity() == 4);

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pub fn push(&mut self, c: char) -> Result<(), ()>

Appends the given char to the end of this String.

Examples

Basic usage:

use heapless::String;

let mut s: String<8> = String::from("abc");

s.push('1').unwrap();
s.push('2').unwrap();
s.push('3').unwrap();

assert!("abc123" == s.as_str());

assert_eq!("abc123", s);

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pub fn truncate(&mut self, new_len: usize)

Shortens this String to the specified length.

If new_len is greater than the string’s current length, this has no effect.

Note that this method has no effect on the allocated capacity of the string

Panics

Panics if new_len does not lie on a char boundary.

Examples

Basic usage:

use heapless::String;

let mut s: String<8> = String::from("hello");

s.truncate(2);

assert_eq!("he", s);

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pub fn pop(&mut self) -> Option<char>

Removes the last character from the string buffer and returns it.

Returns None if this String is empty.

Examples

Basic usage:

use heapless::String;

let mut s: String<8> = String::from("foo");

assert_eq!(s.pop(), Some('o'));
assert_eq!(s.pop(), Some('o'));
assert_eq!(s.pop(), Some('f'));

assert_eq!(s.pop(), None);

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pub fn clear(&mut self)

Truncates this String, removing all contents.

While this means the String will have a length of zero, it does not touch its capacity.

Examples

Basic usage:

use heapless::String;

let mut s: String<8> = String::from("foo");

s.clear();

assert!(s.is_empty());
assert_eq!(0, s.len());
assert_eq!(8, s.capacity());