| //! Ways to create a `str` from bytes slice. |
| |
| use crate::mem; |
| |
| use super::validations::run_utf8_validation; |
| use super::Utf8Error; |
| |
| /// Converts a slice of bytes to a string slice. |
| /// |
| /// A string slice ([`&str`]) is made of bytes ([`u8`]), and a byte slice |
| /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts between |
| /// the two. Not all byte slices are valid string slices, however: [`&str`] requires |
| /// that it is valid UTF-8. `from_utf8()` checks to ensure that the bytes are valid |
| /// UTF-8, and then does the conversion. |
| /// |
| /// [`&str`]: str |
| /// [byteslice]: slice |
| /// |
| /// If you are sure that the byte slice is valid UTF-8, and you don't want to |
| /// incur the overhead of the validity check, there is an unsafe version of |
| /// this function, [`from_utf8_unchecked`], which has the same |
| /// behavior but skips the check. |
| /// |
| /// If you need a `String` instead of a `&str`, consider |
| /// [`String::from_utf8`][string]. |
| /// |
| /// [string]: ../../std/string/struct.String.html#method.from_utf8 |
| /// |
| /// Because you can stack-allocate a `[u8; N]`, and you can take a |
| /// [`&[u8]`][byteslice] of it, this function is one way to have a |
| /// stack-allocated string. There is an example of this in the |
| /// examples section below. |
| /// |
| /// [byteslice]: slice |
| /// |
| /// # Errors |
| /// |
| /// Returns `Err` if the slice is not UTF-8 with a description as to why the |
| /// provided slice is not UTF-8. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// use std::str; |
| /// |
| /// // some bytes, in a vector |
| /// let sparkle_heart = vec![240, 159, 146, 150]; |
| /// |
| /// // We know these bytes are valid, so just use `unwrap()`. |
| /// let sparkle_heart = str::from_utf8(&sparkle_heart).unwrap(); |
| /// |
| /// assert_eq!("💖", sparkle_heart); |
| /// ``` |
| /// |
| /// Incorrect bytes: |
| /// |
| /// ``` |
| /// use std::str; |
| /// |
| /// // some invalid bytes, in a vector |
| /// let sparkle_heart = vec![0, 159, 146, 150]; |
| /// |
| /// assert!(str::from_utf8(&sparkle_heart).is_err()); |
| /// ``` |
| /// |
| /// See the docs for [`Utf8Error`] for more details on the kinds of |
| /// errors that can be returned. |
| /// |
| /// A "stack allocated string": |
| /// |
| /// ``` |
| /// use std::str; |
| /// |
| /// // some bytes, in a stack-allocated array |
| /// let sparkle_heart = [240, 159, 146, 150]; |
| /// |
| /// // We know these bytes are valid, so just use `unwrap()`. |
| /// let sparkle_heart: &str = str::from_utf8(&sparkle_heart).unwrap(); |
| /// |
| /// assert_eq!("💖", sparkle_heart); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[rustc_const_stable(feature = "const_str_from_utf8_shared", since = "1.63.0")] |
| #[rustc_allow_const_fn_unstable(str_internals)] |
| pub const fn from_utf8(v: &[u8]) -> Result<&str, Utf8Error> { |
| // FIXME: This should use `?` again, once it's `const` |
| match run_utf8_validation(v) { |
| Ok(_) => { |
| // SAFETY: validation succeeded. |
| Ok(unsafe { from_utf8_unchecked(v) }) |
| } |
| Err(err) => Err(err), |
| } |
| } |
| |
| /// Converts a mutable slice of bytes to a mutable string slice. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// use std::str; |
| /// |
| /// // "Hello, Rust!" as a mutable vector |
| /// let mut hellorust = vec![72, 101, 108, 108, 111, 44, 32, 82, 117, 115, 116, 33]; |
| /// |
| /// // As we know these bytes are valid, we can use `unwrap()` |
| /// let outstr = str::from_utf8_mut(&mut hellorust).unwrap(); |
| /// |
| /// assert_eq!("Hello, Rust!", outstr); |
| /// ``` |
| /// |
| /// Incorrect bytes: |
| /// |
| /// ``` |
| /// use std::str; |
| /// |
| /// // Some invalid bytes in a mutable vector |
| /// let mut invalid = vec![128, 223]; |
| /// |
| /// assert!(str::from_utf8_mut(&mut invalid).is_err()); |
| /// ``` |
| /// See the docs for [`Utf8Error`] for more details on the kinds of |
| /// errors that can be returned. |
| #[stable(feature = "str_mut_extras", since = "1.20.0")] |
| #[rustc_const_unstable(feature = "const_str_from_utf8", issue = "91006")] |
| pub const fn from_utf8_mut(v: &mut [u8]) -> Result<&mut str, Utf8Error> { |
| // This should use `?` again, once it's `const` |
| match run_utf8_validation(v) { |
| Ok(_) => { |
| // SAFETY: validation succeeded. |
| Ok(unsafe { from_utf8_unchecked_mut(v) }) |
| } |
| Err(err) => Err(err), |
| } |
| } |
| |
| /// Converts a slice of bytes to a string slice without checking |
| /// that the string contains valid UTF-8. |
| /// |
| /// See the safe version, [`from_utf8`], for more information. |
| /// |
| /// # Safety |
| /// |
| /// The bytes passed in must be valid UTF-8. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// use std::str; |
| /// |
| /// // some bytes, in a vector |
| /// let sparkle_heart = vec![240, 159, 146, 150]; |
| /// |
| /// let sparkle_heart = unsafe { |
| /// str::from_utf8_unchecked(&sparkle_heart) |
| /// }; |
| /// |
| /// assert_eq!("💖", sparkle_heart); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[rustc_const_stable(feature = "const_str_from_utf8_unchecked", since = "1.55.0")] |
| pub const unsafe fn from_utf8_unchecked(v: &[u8]) -> &str { |
| // SAFETY: the caller must guarantee that the bytes `v` are valid UTF-8. |
| // Also relies on `&str` and `&[u8]` having the same layout. |
| unsafe { mem::transmute(v) } |
| } |
| |
| /// Converts a slice of bytes to a string slice without checking |
| /// that the string contains valid UTF-8; mutable version. |
| /// |
| /// See the immutable version, [`from_utf8_unchecked()`] for more information. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// use std::str; |
| /// |
| /// let mut heart = vec![240, 159, 146, 150]; |
| /// let heart = unsafe { str::from_utf8_unchecked_mut(&mut heart) }; |
| /// |
| /// assert_eq!("💖", heart); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[stable(feature = "str_mut_extras", since = "1.20.0")] |
| #[rustc_const_unstable(feature = "const_str_from_utf8_unchecked_mut", issue = "91005")] |
| pub const unsafe fn from_utf8_unchecked_mut(v: &mut [u8]) -> &mut str { |
| // SAFETY: the caller must guarantee that the bytes `v` |
| // are valid UTF-8, thus the cast to `*mut str` is safe. |
| // Also, the pointer dereference is safe because that pointer |
| // comes from a reference which is guaranteed to be valid for writes. |
| unsafe { &mut *(v as *mut [u8] as *mut str) } |
| } |