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Rollup merge of #44855 - federicomenaquintero:master, r=steveklabnik
Improved docs for CStr, CString, OsStr, OsString This expands the documentation for those structs and their corresponding traits, per https://github.com/rust-lang/rust/issues/29354
This commit is contained in:
kennytm
GitHub
commit
6c43bd3c83
@ -23,19 +23,69 @@ use ptr;
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use slice;
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use str::{self, Utf8Error};
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/// A type representing an owned C-compatible string.
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/// A type representing an owned, C-compatible, nul-terminated string with no nul bytes in the
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/// middle.
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///
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/// This type serves the primary purpose of being able to safely generate a
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/// This type serves the purpose of being able to safely generate a
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/// C-compatible string from a Rust byte slice or vector. An instance of this
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/// type is a static guarantee that the underlying bytes contain no interior 0
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/// bytes and the final byte is 0.
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/// bytes ("nul characters") and that the final byte is 0 ("nul terminator").
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///
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/// A `CString` is created from either a byte slice or a byte vector. A [`u8`]
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/// slice can be obtained with the `as_bytes` method. Slices produced from a
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/// `CString` do *not* contain the trailing nul terminator unless otherwise
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/// specified.
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/// `CString` is to [`CStr`] as [`String`] is to [`&str`]: the former
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/// in each pair are owned strings; the latter are borrowed
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/// references.
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///
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/// # Creating a `CString`
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///
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/// A `CString` is created from either a byte slice or a byte vector,
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/// or anything that implements [`Into`]`<`[`Vec`]`<`[`u8`]`>>` (for
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/// example, you can build a `CString` straight out of a [`String`] or
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/// a [`&str`], since both implement that trait).
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///
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/// The [`new`] method will actually check that the provided `&[u8]`
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/// does not have 0 bytes in the middle, and return an error if it
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/// finds one.
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///
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/// # Extracting a raw pointer to the whole C string
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///
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/// `CString` implements a [`as_ptr`] method through the [`Deref`]
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/// trait. This method will give you a `*const c_char` which you can
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/// feed directly to extern functions that expect a nul-terminated
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/// string, like C's `strdup()`.
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///
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/// # Extracting a slice of the whole C string
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///
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/// Alternatively, you can obtain a `&[`[`u8`]`]` slice from a
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/// `CString` with the [`as_bytes`] method. Slices produced in this
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/// way do *not* contain the trailing nul terminator. This is useful
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/// when you will be calling an extern function that takes a `*const
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/// u8` argument which is not necessarily nul-terminated, plus another
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/// argument with the length of the string — like C's `strndup()`.
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/// You can of course get the slice's length with its
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/// [`len`][slice.len] method.
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///
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/// If you need a `&[`[`u8`]`]` slice *with* the nul terminator, you
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/// can use [`as_bytes_with_nul`] instead.
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///
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/// Once you have the kind of slice you need (with or without a nul
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/// terminator), you can call the slice's own
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/// [`as_ptr`][slice.as_ptr] method to get a raw pointer to pass to
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/// extern functions. See the documentation for that function for a
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/// discussion on ensuring the lifetime of the raw pointer.
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///
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/// [`Into`]: ../convert/trait.Into.html
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/// [`Vec`]: ../vec/struct.Vec.html
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/// [`String`]: ../string/struct.String.html
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/// [`&str`]: ../primitive.str.html
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/// [`u8`]: ../primitive.u8.html
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/// [`new`]: #method.new
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/// [`as_bytes`]: #method.as_bytes
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/// [`as_bytes_with_nul`]: #method.as_bytes_with_nul
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/// [`as_ptr`]: #method.as_ptr
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/// [slice.as_ptr]: ../primitive.slice.html#method.as_ptr
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/// [slice.len]: ../primitive.slice.html#method.len
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/// [`Deref`]: ../ops/trait.Deref.html
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/// [`CStr`]: struct.CStr.html
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///
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/// # Examples
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///
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@ -48,6 +98,8 @@ use str::{self, Utf8Error};
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/// fn my_printer(s: *const c_char);
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/// }
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///
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/// // We are certain that our string doesn't have 0 bytes in the middle,
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/// // so we can .unwrap()
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/// let c_to_print = CString::new("Hello, world!").unwrap();
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/// unsafe {
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/// my_printer(c_to_print.as_ptr());
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@ -58,7 +110,7 @@ use str::{self, Utf8Error};
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/// # Safety
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///
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/// `CString` is intended for working with traditional C-style strings
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/// (a sequence of non-null bytes terminated by a single null byte); the
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/// (a sequence of non-nul bytes terminated by a single nul byte); the
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/// primary use case for these kinds of strings is interoperating with C-like
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/// code. Often you will need to transfer ownership to/from that external
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/// code. It is strongly recommended that you thoroughly read through the
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@ -77,17 +129,21 @@ pub struct CString {
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/// Representation of a borrowed C string.
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///
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/// This dynamically sized type is only safely constructed via a borrowed
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/// version of an instance of `CString`. This type can be constructed from a raw
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/// C string as well and represents a C string borrowed from another location.
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/// This type represents a borrowed reference to a nul-terminated
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/// array of bytes. It can be constructed safely from a `&[`[`u8`]`]`
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/// slice, or unsafely from a raw `*const c_char`. It can then be
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/// converted to a Rust [`&str`] by performing UTF-8 validation, or
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/// into an owned [`CString`].
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///
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/// `CStr` is to [`CString`] as [`&str`] is to [`String`]: the former
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/// in each pair are borrowed references; the latter are owned
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/// strings.
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///
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/// Note that this structure is **not** `repr(C)` and is not recommended to be
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/// placed in the signatures of FFI functions. Instead safe wrappers of FFI
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/// placed in the signatures of FFI functions. Instead, safe wrappers of FFI
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/// functions may leverage the unsafe [`from_ptr`] constructor to provide a safe
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/// interface to other consumers.
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///
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/// [`from_ptr`]: #method.from_ptr
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///
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/// # Examples
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///
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/// Inspecting a foreign C string:
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@ -100,7 +156,7 @@ pub struct CString {
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///
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/// unsafe {
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/// let slice = CStr::from_ptr(my_string());
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/// println!("string length: {}", slice.to_bytes().len());
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/// println!("string buffer size without nul terminator: {}", slice.to_bytes().len());
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/// }
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/// ```
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///
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@ -122,8 +178,6 @@ pub struct CString {
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///
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/// Converting a foreign C string into a Rust [`String`]:
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///
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/// [`String`]: ../string/struct.String.html
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///
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/// ```no_run
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/// use std::ffi::CStr;
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/// use std::os::raw::c_char;
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@ -138,6 +192,12 @@ pub struct CString {
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///
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/// println!("string: {}", my_string_safe());
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/// ```
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///
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/// [`u8`]: ../primitive.u8.html
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/// [`&str`]: ../primitive.str.html
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/// [`String`]: ../string/struct.String.html
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/// [`CString`]: struct.CString.html
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/// [`from_ptr`]: #method.from_ptr
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#[derive(Hash)]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub struct CStr {
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@ -148,9 +208,15 @@ pub struct CStr {
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inner: [c_char]
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}
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/// An error returned from [`CString::new`] to indicate that a nul byte was found
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/// in the vector provided.
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/// An error indicating that an interior nul byte was found.
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///
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/// While Rust strings may contain nul bytes in the middle, C strings
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/// can't, as that byte would effectively truncate the string.
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///
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/// This error is created by the [`new`][`CString::new`] method on
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/// [`CString`]. See its documentation for more.
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///
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/// [`CString`]: struct.CString.html
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/// [`CString::new`]: struct.CString.html#method.new
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///
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/// # Examples
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@ -164,9 +230,16 @@ pub struct CStr {
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#[stable(feature = "rust1", since = "1.0.0")]
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pub struct NulError(usize, Vec<u8>);
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/// An error returned from [`CStr::from_bytes_with_nul`] to indicate that a nul
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/// byte was found too early in the slice provided or one wasn't found at all.
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/// An error indicating that a nul byte was not in the expected position.
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///
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/// The slice used to create a [`CStr`] must have one and only one nul
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/// byte at the end of the slice.
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///
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/// This error is created by the
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/// [`from_bytes_with_nul`][`CStr::from_bytes_with_nul`] method on
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/// [`CStr`]. See its documentation for more.
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///
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/// [`CStr`]: struct.CStr.html
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/// [`CStr::from_bytes_with_nul`]: struct.CStr.html#method.from_bytes_with_nul
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///
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/// # Examples
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@ -201,9 +274,18 @@ impl FromBytesWithNulError {
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}
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}
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/// An error returned from [`CString::into_string`] to indicate that a UTF-8 error
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/// was encountered during the conversion.
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/// An error indicating invalid UTF-8 when converting a [`CString`] into a [`String`].
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///
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/// `CString` is just a wrapper over a buffer of bytes with a nul
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/// terminator; [`into_string`][`CString::into_string`] performs UTF-8
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/// validation on those bytes and may return this error.
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///
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/// This `struct` is created by the
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/// [`into_string`][`CString::into_string`] method on [`CString`]. See
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/// its documentation for more.
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///
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/// [`String`]: ../string/struct.String.html
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/// [`CString`]: struct.CString.html
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/// [`CString::into_string`]: struct.CString.html#method.into_string
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#[derive(Clone, PartialEq, Eq, Debug)]
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#[stable(feature = "cstring_into", since = "1.7.0")]
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@ -215,8 +297,11 @@ pub struct IntoStringError {
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impl CString {
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/// Creates a new C-compatible string from a container of bytes.
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///
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/// This method will consume the provided data and use the underlying bytes
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/// to construct a new string, ensuring that there is a trailing 0 byte.
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/// This function will consume the provided data and use the
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/// underlying bytes to construct a new string, ensuring that
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/// there is a trailing 0 byte. This trailing 0 byte will be
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/// appended by this function; the provided data should *not*
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/// contain any 0 bytes in it.
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///
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/// # Examples
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///
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@ -234,9 +319,11 @@ impl CString {
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///
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/// # Errors
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///
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/// This function will return an error if the bytes yielded contain an
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/// internal 0 byte. The error returned will contain the bytes as well as
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/// This function will return an error if the supplied bytes contain an
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/// internal 0 byte. The [`NulError`] returned will contain the bytes as well as
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/// the position of the nul byte.
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///
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/// [`NulError`]: struct.NulError.html
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<CString, NulError> {
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Self::_new(t.into())
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@ -249,8 +336,8 @@ impl CString {
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}
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}
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/// Creates a C-compatible string from a byte vector without checking for
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/// interior 0 bytes.
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/// Creates a C-compatible string by consuming a byte vector,
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/// without checking for interior 0 bytes.
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///
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/// This method is equivalent to [`new`] except that no runtime assertion
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/// is made that `v` contains no 0 bytes, and it requires an actual
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@ -275,7 +362,7 @@ impl CString {
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CString { inner: v.into_boxed_slice() }
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}
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/// Retakes ownership of a `CString` that was transferred to C.
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/// Retakes ownership of a `CString` that was transferred to C via [`into_raw`].
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///
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/// Additionally, the length of the string will be recalculated from the pointer.
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///
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@ -286,7 +373,14 @@ impl CString {
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/// ownership of a string that was allocated by foreign code) is likely to lead
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/// to undefined behavior or allocator corruption.
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///
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/// > **Note:** If you need to borrow a string that was allocated by
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/// > foreign code, use [`CStr`]. If you need to take ownership of
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/// > a string that was allocated by foreign code, you will need to
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/// > make your own provisions for freeing it appropriately, likely
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/// > with the foreign code's API to do that.
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///
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/// [`into_raw`]: #method.into_raw
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/// [`CStr`]: struct.CStr.html
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///
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/// # Examples
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///
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@ -315,11 +409,11 @@ impl CString {
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CString { inner: Box::from_raw(slice as *mut [c_char] as *mut [u8]) }
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}
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/// Transfers ownership of the string to a C caller.
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/// Consumes the `CString` and transfers ownership of the string to a C caller.
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///
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/// The pointer must be returned to Rust and reconstituted using
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/// The pointer which this function returns must be returned to Rust and reconstituted using
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/// [`from_raw`] to be properly deallocated. Specifically, one
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/// should *not* use the standard C `free` function to deallocate
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/// should *not* use the standard C `free()` function to deallocate
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/// this string.
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///
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/// Failure to call [`from_raw`] will lead to a memory leak.
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@ -351,11 +445,27 @@ impl CString {
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Box::into_raw(self.into_inner()) as *mut c_char
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}
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/// Converts the `CString` into a [`String`] if it contains valid Unicode data.
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/// Converts the `CString` into a [`String`] if it contains valid UTF-8 data.
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///
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/// On failure, ownership of the original `CString` is returned.
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///
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/// [`String`]: ../string/struct.String.html
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///
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/// # Examples
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///
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/// ```
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/// use std::ffi::CString;
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///
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/// let valid_utf8 = vec![b'f', b'o', b'o'];
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/// let cstring = CString::new(valid_utf8).unwrap();
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/// assert_eq!(cstring.into_string().unwrap(), "foo");
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///
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/// let invalid_utf8 = vec![b'f', 0xff, b'o', b'o'];
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/// let cstring = CString::new(invalid_utf8).unwrap();
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/// let err = cstring.into_string().err().unwrap();
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/// assert_eq!(err.utf8_error().valid_up_to(), 1);
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/// ```
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#[stable(feature = "cstring_into", since = "1.7.0")]
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pub fn into_string(self) -> Result<String, IntoStringError> {
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String::from_utf8(self.into_bytes())
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@ -365,10 +475,11 @@ impl CString {
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})
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}
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/// Returns the underlying byte buffer.
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/// Consumes the `CString` and returns the underlying byte buffer.
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///
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/// The returned buffer does **not** contain the trailing nul separator and
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/// it is guaranteed to not have any interior nul bytes.
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/// The returned buffer does **not** contain the trailing nul
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/// terminator, and it is guaranteed to not have any interior nul
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/// bytes.
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///
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/// # Examples
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///
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@ -388,7 +499,7 @@ impl CString {
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}
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/// Equivalent to the [`into_bytes`] function except that the returned vector
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/// includes the trailing nul byte.
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/// includes the trailing nul terminator.
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///
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/// [`into_bytes`]: #method.into_bytes
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///
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@ -408,8 +519,12 @@ impl CString {
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/// Returns the contents of this `CString` as a slice of bytes.
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///
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/// The returned slice does **not** contain the trailing nul separator and
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/// it is guaranteed to not have any interior nul bytes.
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/// The returned slice does **not** contain the trailing nul
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/// terminator, and it is guaranteed to not have any interior nul
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/// bytes. If you need the nul terminator, use
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/// [`as_bytes_with_nul`] instead.
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///
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/// [`as_bytes_with_nul`]: #method.as_bytes_with_nul
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///
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/// # Examples
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///
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@ -427,7 +542,7 @@ impl CString {
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}
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/// Equivalent to the [`as_bytes`] function except that the returned slice
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/// includes the trailing nul byte.
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/// includes the trailing nul terminator.
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///
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/// [`as_bytes`]: #method.as_bytes
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///
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@ -598,8 +713,8 @@ impl Default for Box<CStr> {
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}
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impl NulError {
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/// Returns the position of the nul byte in the slice that was provided to
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/// [`CString::new`].
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/// Returns the position of the nul byte in the slice that caused
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/// [`CString::new`] to fail.
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///
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/// [`CString::new`]: struct.CString.html#method.new
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///
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@ -711,9 +826,9 @@ impl fmt::Display for IntoStringError {
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}
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impl CStr {
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/// Casts a raw C string to a safe C string wrapper.
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/// Wraps a raw C string with a safe C string wrapper.
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///
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/// This function will cast the provided `ptr` to the `CStr` wrapper which
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/// This function will wrap the provided `ptr` with a `CStr` wrapper, which
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/// allows inspection and interoperation of non-owned C strings. This method
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/// is unsafe for a number of reasons:
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///
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@ -753,9 +868,9 @@ impl CStr {
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/// Creates a C string wrapper from a byte slice.
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///
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/// This function will cast the provided `bytes` to a `CStr` wrapper after
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/// ensuring that it is null terminated and does not contain any interior
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/// nul bytes.
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/// This function will cast the provided `bytes` to a `CStr`
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/// wrapper after ensuring that the byte slice is nul-terminated
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/// and does not contain any interior nul bytes.
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///
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/// # Examples
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///
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@ -766,7 +881,7 @@ impl CStr {
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/// assert!(cstr.is_ok());
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/// ```
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///
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/// Creating a `CStr` without a trailing nul byte is an error:
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/// Creating a `CStr` without a trailing nul terminator is an error:
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///
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/// ```
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/// use std::ffi::CStr;
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@ -800,7 +915,7 @@ impl CStr {
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/// Unsafely creates a C string wrapper from a byte slice.
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///
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/// This function will cast the provided `bytes` to a `CStr` wrapper without
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/// performing any sanity checks. The provided slice must be null terminated
|
||||
/// performing any sanity checks. The provided slice **must** be nul-terminated
|
||||
/// and not contain any interior nul bytes.
|
||||
///
|
||||
/// # Examples
|
||||
@ -822,7 +937,7 @@ impl CStr {
|
||||
|
||||
/// Returns the inner pointer to this C string.
|
||||
///
|
||||
/// The returned pointer will be valid for as long as `self` is and points
|
||||
/// The returned pointer will be valid for as long as `self` is, and points
|
||||
/// to a contiguous region of memory terminated with a 0 byte to represent
|
||||
/// the end of the string.
|
||||
///
|
||||
@ -843,9 +958,9 @@ impl CStr {
|
||||
/// ```
|
||||
///
|
||||
/// This happens because the pointer returned by `as_ptr` does not carry any
|
||||
/// lifetime information and the string is deallocated immediately after
|
||||
/// lifetime information and the [`CString`] is deallocated immediately after
|
||||
/// the `CString::new("Hello").unwrap().as_ptr()` expression is evaluated.
|
||||
/// To fix the problem, bind the string to a local variable:
|
||||
/// To fix the problem, bind the `CString` to a local variable:
|
||||
///
|
||||
/// ```no_run
|
||||
/// use std::ffi::{CString};
|
||||
@ -857,6 +972,11 @@ impl CStr {
|
||||
/// *ptr;
|
||||
/// }
|
||||
/// ```
|
||||
///
|
||||
/// This way, the lifetime of the `CString` in `hello` encompasses
|
||||
/// the lifetime of `ptr` and the `unsafe` block.
|
||||
///
|
||||
/// [`CString`]: struct.CString.html
|
||||
#[inline]
|
||||
#[stable(feature = "rust1", since = "1.0.0")]
|
||||
pub fn as_ptr(&self) -> *const c_char {
|
||||
@ -865,11 +985,7 @@ impl CStr {
|
||||
|
||||
/// Converts this C string to a byte slice.
|
||||
///
|
||||
/// This function will calculate the length of this string (which normally
|
||||
/// requires a linear amount of work to be done) and then return the
|
||||
/// resulting slice of `u8` elements.
|
||||
///
|
||||
/// The returned slice will **not** contain the trailing nul that this C
|
||||
/// The returned slice will **not** contain the trailing nul terminator that this C
|
||||
/// string has.
|
||||
///
|
||||
/// > **Note**: This method is currently implemented as a 0-cost cast, but
|
||||
@ -894,7 +1010,7 @@ impl CStr {
|
||||
/// Converts this C string to a byte slice containing the trailing 0 byte.
|
||||
///
|
||||
/// This function is the equivalent of [`to_bytes`] except that it will retain
|
||||
/// the trailing nul instead of chopping it off.
|
||||
/// the trailing nul terminator instead of chopping it off.
|
||||
///
|
||||
/// > **Note**: This method is currently implemented as a 0-cost cast, but
|
||||
/// > it is planned to alter its definition in the future to perform the
|
||||
@ -918,8 +1034,9 @@ impl CStr {
|
||||
|
||||
/// Yields a [`&str`] slice if the `CStr` contains valid UTF-8.
|
||||
///
|
||||
/// This function will calculate the length of this string and check for
|
||||
/// UTF-8 validity, and then return the [`&str`] if it's valid.
|
||||
/// If the contents of the `CStr` are valid UTF-8 data, this
|
||||
/// function will return the corresponding [`&str`] slice. Otherwise,
|
||||
/// it will return an error with details of where UTF-8 validation failed.
|
||||
///
|
||||
/// > **Note**: This method is currently implemented to check for validity
|
||||
/// > after a 0-cost cast, but it is planned to alter its definition in the
|
||||
@ -947,10 +1064,12 @@ impl CStr {
|
||||
|
||||
/// Converts a `CStr` into a [`Cow`]`<`[`str`]`>`.
|
||||
///
|
||||
/// This function will calculate the length of this string (which normally
|
||||
/// requires a linear amount of work to be done) and then return the
|
||||
/// resulting slice as a [`Cow`]`<`[`str`]`>`, replacing any invalid UTF-8 sequences
|
||||
/// with `U+FFFD REPLACEMENT CHARACTER`.
|
||||
/// If the contents of the `CStr` are valid UTF-8 data, this
|
||||
/// function will return a [`Cow`]`::`[`Borrowed`]`(`[`&str`]`)`
|
||||
/// with the the corresponding [`&str`] slice. Otherwise, it will
|
||||
/// replace any invalid UTF-8 sequences with `U+FFFD REPLACEMENT
|
||||
/// CHARACTER` and return a [`Cow`]`::`[`Owned`]`(`[`String`]`)`
|
||||
/// with the result.
|
||||
///
|
||||
/// > **Note**: This method is currently implemented to check for validity
|
||||
/// > after a 0-cost cast, but it is planned to alter its definition in the
|
||||
@ -958,7 +1077,9 @@ impl CStr {
|
||||
/// > check whenever this method is called.
|
||||
///
|
||||
/// [`Cow`]: ../borrow/enum.Cow.html
|
||||
/// [`Borrowed`]: ../borrow/enum.Cow.html#variant.Borrowed
|
||||
/// [`str`]: ../primitive.str.html
|
||||
/// [`String`]: ../string/struct.String.html
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
|
||||
@ -9,6 +9,157 @@
|
||||
// except according to those terms.
|
||||
|
||||
//! Utilities related to FFI bindings.
|
||||
//!
|
||||
//! This module provides utilities to handle data across non-Rust
|
||||
//! interfaces, like other programming languages and the underlying
|
||||
//! operating system. It is mainly of use for FFI (Foreign Function
|
||||
//! Interface) bindings and code that needs to exchange C-like strings
|
||||
//! with other languages.
|
||||
//!
|
||||
//! # Overview
|
||||
//!
|
||||
//! Rust represents owned strings with the [`String`] type, and
|
||||
//! borrowed slices of strings with the [`str`] primitive. Both are
|
||||
//! always in UTF-8 encoding, and may contain nul bytes in the middle,
|
||||
//! i.e. if you look at the bytes that make up the string, there may
|
||||
//! be a `\0` among them. Both `String` and `str` store their length
|
||||
//! explicitly; there are no nul terminators at the end of strings
|
||||
//! like in C.
|
||||
//!
|
||||
//! C strings are different from Rust strings:
|
||||
//!
|
||||
//! * **Encodings** - Rust strings are UTF-8, but C strings may use
|
||||
//! other encodings. If you are using a string from C, you should
|
||||
//! check its encoding explicitly, rather than just assuming that it
|
||||
//! is UTF-8 like you can do in Rust.
|
||||
//!
|
||||
//! * **Character size** - C strings may use `char` or `wchar_t`-sized
|
||||
//! characters; please **note** that C's `char` is different from Rust's.
|
||||
//! The C standard leaves the actual sizes of those types open to
|
||||
//! interpretation, but defines different APIs for strings made up of
|
||||
//! each character type. Rust strings are always UTF-8, so different
|
||||
//! Unicode characters will be encoded in a variable number of bytes
|
||||
//! each. The Rust type [`char`] represents a '[Unicode scalar
|
||||
//! value]', which is similar to, but not the same as, a '[Unicode
|
||||
//! code point]'.
|
||||
//!
|
||||
//! * **Nul terminators and implicit string lengths** - Often, C
|
||||
//! strings are nul-terminated, i.e. they have a `\0` character at the
|
||||
//! end. The length of a string buffer is not stored, but has to be
|
||||
//! calculated; to compute the length of a string, C code must
|
||||
//! manually call a function like `strlen()` for `char`-based strings,
|
||||
//! or `wcslen()` for `wchar_t`-based ones. Those functions return
|
||||
//! the number of characters in the string excluding the nul
|
||||
//! terminator, so the buffer length is really `len+1` characters.
|
||||
//! Rust strings don't have a nul terminator; their length is always
|
||||
//! stored and does not need to be calculated. While in Rust
|
||||
//! accessing a string's length is a O(1) operation (becasue the
|
||||
//! length is stored); in C it is an O(length) operation because the
|
||||
//! length needs to be computed by scanning the string for the nul
|
||||
//! terminator.
|
||||
//!
|
||||
//! * **Internal nul characters** - When C strings have a nul
|
||||
//! terminator character, this usually means that they cannot have nul
|
||||
//! characters in the middle — a nul character would essentially
|
||||
//! truncate the string. Rust strings *can* have nul characters in
|
||||
//! the middle, because nul does not have to mark the end of the
|
||||
//! string in Rust.
|
||||
//!
|
||||
//! # Representations of non-Rust strings
|
||||
//!
|
||||
//! [`CString`] and [`CStr`] are useful when you need to transfer
|
||||
//! UTF-8 strings to and from languages with a C ABI, like Python.
|
||||
//!
|
||||
//! * **From Rust to C:** [`CString`] represents an owned, C-friendly
|
||||
//! string: it is nul-terminated, and has no internal nul characters.
|
||||
//! Rust code can create a `CString` out of a normal string (provided
|
||||
//! that the string doesn't have nul characters in the middle), and
|
||||
//! then use a variety of methods to obtain a raw `*mut u8` that can
|
||||
//! then be passed as an argument to functions which use the C
|
||||
//! conventions for strings.
|
||||
//!
|
||||
//! * **From C to Rust:** [`CStr`] represents a borrowed C string; it
|
||||
//! is what you would use to wrap a raw `*const u8` that you got from
|
||||
//! a C function. A `CStr` is guaranteed to be a nul-terminated array
|
||||
//! of bytes. Once you have a `CStr`, you can convert it to a Rust
|
||||
//! `&str` if it's valid UTF-8, or lossily convert it by adding
|
||||
//! replacement characters.
|
||||
//!
|
||||
//! [`OsString`] and [`OsStr`] are useful when you need to transfer
|
||||
//! strings to and from the operating system itself, or when capturing
|
||||
//! the output of external commands. Conversions between `OsString`,
|
||||
//! `OsStr` and Rust strings work similarly to those for [`CString`]
|
||||
//! and [`CStr`].
|
||||
//!
|
||||
//! * [`OsString`] represents an owned string in whatever
|
||||
//! representation the operating system prefers. In the Rust standard
|
||||
//! library, various APIs that transfer strings to/from the operating
|
||||
//! system use `OsString` instead of plain strings. For example,
|
||||
//! [`env::var_os()`] is used to query environment variables; it
|
||||
//! returns an `Option<OsString>`. If the environment variable exists
|
||||
//! you will get a `Some(os_string)`, which you can *then* try to
|
||||
//! convert to a Rust string. This yields a [`Result<>`], so that
|
||||
//! your code can detect errors in case the environment variable did
|
||||
//! not in fact contain valid Unicode data.
|
||||
//!
|
||||
//! * [`OsStr`] represents a borrowed reference to a string in a
|
||||
//! format that can be passed to the operating system. It can be
|
||||
//! converted into an UTF-8 Rust string slice in a similar way to
|
||||
//! `OsString`.
|
||||
//!
|
||||
//! # Conversions
|
||||
//!
|
||||
//! ## On Unix
|
||||
//!
|
||||
//! On Unix, [`OsStr`] implements the
|
||||
//! `std::os::unix:ffi::`[`OsStrExt`][unix.OsStrExt] trait, which
|
||||
//! augments it with two methods, [`from_bytes`] and [`as_bytes`].
|
||||
//! These do inexpensive conversions from and to UTF-8 byte slices.
|
||||
//!
|
||||
//! Additionally, on Unix [`OsString`] implements the
|
||||
//! `std::os::unix:ffi::`[`OsStringExt`][unix.OsStringExt] trait,
|
||||
//! which provides [`from_vec`] and [`into_vec`] methods that consume
|
||||
//! their arguments, and take or produce vectors of [`u8`].
|
||||
//!
|
||||
//! ## On Windows
|
||||
//!
|
||||
//! On Windows, [`OsStr`] implements the
|
||||
//! `std::os::windows::ffi::`[`OsStrExt`][windows.OsStrExt] trait,
|
||||
//! which provides an [`encode_wide`] method. This provides an
|
||||
//! iterator that can be [`collect`]ed into a vector of [`u16`].
|
||||
//!
|
||||
//! Additionally, on Windows [`OsString`] implements the
|
||||
//! `std::os::windows:ffi::`[`OsStringExt`][windows.OsStringExt]
|
||||
//! trait, which provides a [`from_wide`] method. The result of this
|
||||
//! method is an `OsString` which can be round-tripped to a Windows
|
||||
//! string losslessly.
|
||||
//!
|
||||
//! [`String`]: ../string/struct.String.html
|
||||
//! [`str`]: ../primitive.str.html
|
||||
//! [`char`]: ../primitive.char.html
|
||||
//! [`u8`]: ../primitive.u8.html
|
||||
//! [`u16`]: ../primitive.u16.html
|
||||
//! [Unicode scalar value]: http://www.unicode.org/glossary/#unicode_scalar_value
|
||||
//! [Unicode code point]: http://www.unicode.org/glossary/#code_point
|
||||
//! [`CString`]: struct.CString.html
|
||||
//! [`CStr`]: struct.CStr.html
|
||||
//! [`OsString`]: struct.OsString.html
|
||||
//! [`OsStr`]: struct.OsStr.html
|
||||
//! [`env::set_var()`]: ../env/fn.set_var.html
|
||||
//! [`env::var_os()`]: ../env/fn.var_os.html
|
||||
//! [`Result<>`]: ../result/enum.Result.html
|
||||
//! [unix.OsStringExt]: ../os/unix/ffi/trait.OsStringExt.html
|
||||
//! [`from_vec`]: ../os/unix/ffi/trait.OsStringExt.html#tymethod.from_vec
|
||||
//! [`into_vec`]: ../os/unix/ffi/trait.OsStringExt.html#tymethod.into_vec
|
||||
//! [unix.OsStrExt]: ../os/unix/ffi/trait.OsStrExt.html
|
||||
//! [`from_bytes`]: ../os/unix/ffi/trait.OsStrExt.html#tymethod.from_bytes
|
||||
//! [`as_bytes`]: ../os/unix/ffi/trait.OsStrExt.html#tymethod.as_bytes
|
||||
//! [`OsStrExt`]: ../os/unix/ffi/trait.OsStrExt.html
|
||||
//! [windows.OsStrExt]: ../os/windows/ffi/trait.OsStrExt.html
|
||||
//! [`encode_wide`]: ../os/windows/ffi/trait.OsStrExt.html#tymethod.encode_wide
|
||||
//! [`collect`]: ../iter/trait.Iterator.html#method.collect
|
||||
//! [windows.OsStringExt]: ../os/windows/ffi/trait.OsStringExt.html
|
||||
//! [`from_wide`]: ../os/windows/ffi/trait.OsStringExt.html#tymethod.from_wide
|
||||
|
||||
#![stable(feature = "rust1", since = "1.0.0")]
|
||||
|
||||
|
||||
@ -32,18 +32,65 @@ use sys_common::{AsInner, IntoInner, FromInner};
|
||||
///
|
||||
/// `OsString` and [`OsStr`] bridge this gap by simultaneously representing Rust
|
||||
/// and platform-native string values, and in particular allowing a Rust string
|
||||
/// to be converted into an "OS" string with no cost.
|
||||
/// to be converted into an "OS" string with no cost if possible.
|
||||
///
|
||||
/// `OsString` is to [`OsStr`] as [`String`] is to [`&str`]: the former
|
||||
/// in each pair are owned strings; the latter are borrowed
|
||||
/// references.
|
||||
///
|
||||
/// # Creating an `OsString`
|
||||
///
|
||||
/// **From a Rust string**: `OsString` implements
|
||||
/// [`From`]`<`[`String`]`>`, so you can use `my_string.`[`from`] to
|
||||
/// create an `OsString` from a normal Rust string.
|
||||
///
|
||||
/// **From slices:** Just like you can start with an empty Rust
|
||||
/// [`String`] and then [`push_str`][String.push_str] `&str`
|
||||
/// sub-string slices into it, you can create an empty `OsString` with
|
||||
/// the [`new`] method and then push string slices into it with the
|
||||
/// [`push`] method.
|
||||
///
|
||||
/// # Extracting a borrowed reference to the whole OS string
|
||||
///
|
||||
/// You can use the [`as_os_str`] method to get an `&`[`OsStr`] from
|
||||
/// an `OsString`; this is effectively a borrowed reference to the
|
||||
/// whole string.
|
||||
///
|
||||
/// # Conversions
|
||||
///
|
||||
/// See the [module's toplevel documentation about conversions][conversions] for a discussion on
|
||||
/// the traits which `OsString` implements for conversions from/to native representations.
|
||||
///
|
||||
/// [`OsStr`]: struct.OsStr.html
|
||||
/// [`From`]: ../convert/trait.From.html
|
||||
/// [`from`]: ../convert/trait.From.html#tymethod.from
|
||||
/// [`String`]: ../string/struct.String.html
|
||||
/// [`&str`]: ../primitive.str.html
|
||||
/// [`u8`]: ../primitive.u8.html
|
||||
/// [`u16`]: ../primitive.u16.html
|
||||
/// [String.push_str]: ../string/struct.String.html#method.push_str
|
||||
/// [`new`]: #method.new
|
||||
/// [`push`]: #method.push
|
||||
/// [`as_os_str`]: #method.as_os_str
|
||||
#[derive(Clone)]
|
||||
#[stable(feature = "rust1", since = "1.0.0")]
|
||||
pub struct OsString {
|
||||
inner: Buf
|
||||
}
|
||||
|
||||
/// Slices into OS strings (see [`OsString`]).
|
||||
/// Borrowed reference to an OS string (see [`OsString`]).
|
||||
///
|
||||
/// This type represents a borrowed reference to a string in the operating system's preferred
|
||||
/// representation.
|
||||
///
|
||||
/// `OsStr` is to [`OsString`] as [`String`] is to [`&str`]: the former in each pair are borrowed
|
||||
/// references; the latter are owned strings.
|
||||
///
|
||||
/// See the [module's toplevel documentation about conversions][conversions] for a discussion on
|
||||
/// the traits which `OsStr` implements for conversions from/to native representations.
|
||||
///
|
||||
/// [`OsString`]: struct.OsString.html
|
||||
/// [conversions]: index.html#conversions
|
||||
#[stable(feature = "rust1", since = "1.0.0")]
|
||||
pub struct OsStr {
|
||||
inner: Slice
|
||||
|
||||
@ -9,6 +9,62 @@
|
||||
// except according to those terms.
|
||||
|
||||
//! Windows-specific extensions to the primitives in the `std::ffi` module.
|
||||
//!
|
||||
//! # Overview
|
||||
//!
|
||||
//! For historical reasons, the Windows API uses a form of potentially
|
||||
//! ill-formed UTF-16 encoding for strings. Specifically, the 16-bit
|
||||
//! code units in Windows strings may contain [isolated surrogate code
|
||||
//! points which are not paired together][ill-formed-utf-16]. The
|
||||
//! Unicode standard requires that surrogate code points (those in the
|
||||
//! range U+D800 to U+DFFF) always be *paired*, because in the UTF-16
|
||||
//! encoding a *surrogate code unit pair* is used to encode a single
|
||||
//! character. For compatibility with code that does not enforce
|
||||
//! these pairings, Windows does not enforce them, either.
|
||||
//!
|
||||
//! While it is not always possible to convert such a string losslessly into
|
||||
//! a valid UTF-16 string (or even UTF-8), it is often desirable to be
|
||||
//! able to round-trip such a string from and to Windows APIs
|
||||
//! losslessly. For example, some Rust code may be "bridging" some
|
||||
//! Windows APIs together, just passing `WCHAR` strings among those
|
||||
//! APIs without ever really looking into the strings.
|
||||
//!
|
||||
//! If Rust code *does* need to look into those strings, it can
|
||||
//! convert them to valid UTF-8, possibly lossily, by substituting
|
||||
//! invalid sequences with U+FFFD REPLACEMENT CHARACTER, as is
|
||||
//! conventionally done in other Rust APIs that deal with string
|
||||
//! encodings.
|
||||
//!
|
||||
//! # `OsStringExt` and `OsStrExt`
|
||||
//!
|
||||
//! [`OsString`] is the Rust wrapper for owned strings in the
|
||||
//! preferred representation of the operating system. On Windows,
|
||||
//! this struct gets augmented with an implementation of the
|
||||
//! [`OsStringExt`] trait, which has a [`from_wide`] method. This
|
||||
//! lets you create an [`OsString`] from a `&[u16]` slice; presumably
|
||||
//! you get such a slice out of a `WCHAR` Windows API.
|
||||
//!
|
||||
//! Similarly, [`OsStr`] is the Rust wrapper for borrowed strings from
|
||||
//! preferred representation of the operating system. On Windows, the
|
||||
//! [`OsStrExt`] trait provides the [`encode_wide`] method, which
|
||||
//! outputs an [`EncodeWide`] iterator. You can [`collect`] this
|
||||
//! iterator, for example, to obtain a `Vec<u16>`; you can later get a
|
||||
//! pointer to this vector's contents and feed it to Windows APIs.
|
||||
//!
|
||||
//! These traits, along with [`OsString`] and [`OsStr`], work in
|
||||
//! conjunction so that it is possible to **round-trip** strings from
|
||||
//! Windows and back, with no loss of data, even if the strings are
|
||||
//! ill-formed UTF-16.
|
||||
//!
|
||||
//! [ill-formed-utf-16]: https://simonsapin.github.io/wtf-8/#ill-formed-utf-16
|
||||
//! [`OsString`]: ../../../ffi/struct.OsString.html
|
||||
//! [`OsStr`]: ../../../ffi/struct.OsStr.html
|
||||
//! [`OsStringExt`]: trait.OsStringExt.html
|
||||
//! [`OsStrExt`]: trait.OsStrExt.html
|
||||
//! [`EncodeWide`]: struct.EncodeWide.html
|
||||
//! [`from_wide`]: trait.OsStringExt.html#tymethod.from_wide
|
||||
//! [`encode_wide`]: trait.OsStrExt.html#tymethod.encode_wide
|
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//! [`collect`]: ../../../iter/trait.Iterator.html#method.collect
|
||||
|
||||
#![stable(feature = "rust1", since = "1.0.0")]
|
||||
|
||||
|
||||
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Reference in New Issue
Block a user