40b0026a2f
Rustdoc has no way to show that an item is stable, but only at a different path. `std::ffi::c_str::NulError` is not stable, but `std::ffi::NulError` is. To avoid marking these types as unstable when someone just wants to follow a link from `CString`, inline them into their stable paths.
205 lines
9.8 KiB
Rust
205 lines
9.8 KiB
Rust
//! Utilities related to FFI bindings.
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//!
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//! This module provides utilities to handle data across non-Rust
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//! interfaces, like other programming languages and the underlying
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//! operating system. It is mainly of use for FFI (Foreign Function
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//! Interface) bindings and code that needs to exchange C-like strings
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//! with other languages.
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//!
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//! # Overview
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//!
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//! Rust represents owned strings with the [`String`] type, and
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//! borrowed slices of strings with the [`str`] primitive. Both are
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//! always in UTF-8 encoding, and may contain nul bytes in the middle,
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//! i.e., if you look at the bytes that make up the string, there may
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//! be a `\0` among them. Both `String` and `str` store their length
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//! explicitly; there are no nul terminators at the end of strings
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//! like in C.
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//!
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//! C strings are different from Rust strings:
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//!
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//! * **Encodings** - Rust strings are UTF-8, but C strings may use
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//! other encodings. If you are using a string from C, you should
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//! check its encoding explicitly, rather than just assuming that it
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//! is UTF-8 like you can do in Rust.
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//!
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//! * **Character size** - C strings may use `char` or `wchar_t`-sized
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//! characters; please **note** that C's `char` is different from Rust's.
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//! The C standard leaves the actual sizes of those types open to
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//! interpretation, but defines different APIs for strings made up of
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//! each character type. Rust strings are always UTF-8, so different
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//! Unicode characters will be encoded in a variable number of bytes
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//! each. The Rust type [`char`] represents a '[Unicode scalar
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//! value]', which is similar to, but not the same as, a '[Unicode
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//! code point]'.
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//!
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//! * **Nul terminators and implicit string lengths** - Often, C
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//! strings are nul-terminated, i.e., they have a `\0` character at the
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//! end. The length of a string buffer is not stored, but has to be
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//! calculated; to compute the length of a string, C code must
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//! manually call a function like `strlen()` for `char`-based strings,
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//! or `wcslen()` for `wchar_t`-based ones. Those functions return
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//! the number of characters in the string excluding the nul
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//! terminator, so the buffer length is really `len+1` characters.
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//! Rust strings don't have a nul terminator; their length is always
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//! stored and does not need to be calculated. While in Rust
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//! accessing a string's length is an *O*(1) operation (because the
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//! length is stored); in C it is an *O*(*n*) operation because the
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//! length needs to be computed by scanning the string for the nul
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//! terminator.
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//!
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//! * **Internal nul characters** - When C strings have a nul
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//! terminator character, this usually means that they cannot have nul
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//! characters in the middle — a nul character would essentially
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//! truncate the string. Rust strings *can* have nul characters in
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//! the middle, because nul does not have to mark the end of the
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//! string in Rust.
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//!
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//! # Representations of non-Rust strings
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//!
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//! [`CString`] and [`CStr`] are useful when you need to transfer
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//! UTF-8 strings to and from languages with a C ABI, like Python.
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//!
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//! * **From Rust to C:** [`CString`] represents an owned, C-friendly
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//! string: it is nul-terminated, and has no internal nul characters.
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//! Rust code can create a [`CString`] out of a normal string (provided
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//! that the string doesn't have nul characters in the middle), and
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//! then use a variety of methods to obtain a raw <code>\*mut [u8]</code> that can
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//! then be passed as an argument to functions which use the C
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//! conventions for strings.
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//!
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//! * **From C to Rust:** [`CStr`] represents a borrowed C string; it
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//! is what you would use to wrap a raw <code>\*const [u8]</code> that you got from
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//! a C function. A [`CStr`] is guaranteed to be a nul-terminated array
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//! of bytes. Once you have a [`CStr`], you can convert it to a Rust
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//! <code>&[str]</code> if it's valid UTF-8, or lossily convert it by adding
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//! replacement characters.
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//!
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//! [`OsString`] and [`OsStr`] are useful when you need to transfer
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//! strings to and from the operating system itself, or when capturing
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//! the output of external commands. Conversions between [`OsString`],
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//! [`OsStr`] and Rust strings work similarly to those for [`CString`]
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//! and [`CStr`].
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//!
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//! * [`OsString`] losslessly represents an owned platform string. However, this
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//! representation is not necessarily in a form native to the platform.
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//! In the Rust standard library, various APIs that transfer strings to/from the operating
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//! system use [`OsString`] instead of plain strings. For example,
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//! [`env::var_os()`] is used to query environment variables; it
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//! returns an <code>[Option]<[OsString]></code>. If the environment variable
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//! exists you will get a <code>[Some]\(os_string)</code>, which you can
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//! *then* try to convert to a Rust string. This yields a [`Result`], so that
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//! your code can detect errors in case the environment variable did
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//! not in fact contain valid Unicode data.
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//!
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//! * [`OsStr`] losslessly represents a borrowed reference to a platform string.
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//! However, this representation is not necessarily in a form native to the platform.
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//! It can be converted into a UTF-8 Rust string slice in a similar way to
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//! [`OsString`].
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//!
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//! # Conversions
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//!
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//! ## On Unix
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//!
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//! On Unix, [`OsStr`] implements the
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//! <code>std::os::unix::ffi::[OsStrExt][unix.OsStrExt]</code> trait, which
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//! augments it with two methods, [`from_bytes`] and [`as_bytes`].
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//! These do inexpensive conversions from and to byte slices.
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//!
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//! Additionally, on Unix [`OsString`] implements the
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//! <code>std::os::unix::ffi::[OsStringExt][unix.OsStringExt]</code> trait,
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//! which provides [`from_vec`] and [`into_vec`] methods that consume
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//! their arguments, and take or produce vectors of [`u8`].
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//!
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//! ## On Windows
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//!
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//! An [`OsStr`] can be losslessly converted to a native Windows string. And
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//! a native Windows string can be losslessly converted to an [`OsString`].
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//!
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//! On Windows, [`OsStr`] implements the
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//! <code>std::os::windows::ffi::[OsStrExt][windows.OsStrExt]</code> trait,
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//! which provides an [`encode_wide`] method. This provides an
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//! iterator that can be [`collect`]ed into a vector of [`u16`]. After a nul
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//! characters is appended, this is the same as a native Windows string.
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//!
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//! Additionally, on Windows [`OsString`] implements the
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//! <code>std::os::windows:ffi::[OsStringExt][windows.OsStringExt]</code>
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//! trait, which provides a [`from_wide`] method to convert a native Windows
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//! string (without the terminating nul character) to an [`OsString`].
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//!
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//! ## Other platforms
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//!
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//! Many other platforms provide their own extension traits in a
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//! `std::os::*::ffi` module.
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//!
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//! ## On all platforms
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//!
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//! On all platforms, [`OsStr`] consists of a sequence of bytes that is encoded as a superset of
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//! UTF-8; see [`OsString`] for more details on its encoding on different platforms.
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//!
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//! For limited, inexpensive conversions from and to bytes, see [`OsStr::as_encoded_bytes`] and
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//! [`OsStr::from_encoded_bytes_unchecked`].
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//!
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//! For basic string processing, see [`OsStr::slice_encoded_bytes`].
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//!
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//! [Unicode scalar value]: https://www.unicode.org/glossary/#unicode_scalar_value
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//! [Unicode code point]: https://www.unicode.org/glossary/#code_point
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//! [`env::set_var()`]: crate::env::set_var "env::set_var"
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//! [`env::var_os()`]: crate::env::var_os "env::var_os"
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//! [unix.OsStringExt]: crate::os::unix::ffi::OsStringExt "os::unix::ffi::OsStringExt"
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//! [`from_vec`]: crate::os::unix::ffi::OsStringExt::from_vec "os::unix::ffi::OsStringExt::from_vec"
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//! [`into_vec`]: crate::os::unix::ffi::OsStringExt::into_vec "os::unix::ffi::OsStringExt::into_vec"
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//! [unix.OsStrExt]: crate::os::unix::ffi::OsStrExt "os::unix::ffi::OsStrExt"
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//! [`from_bytes`]: crate::os::unix::ffi::OsStrExt::from_bytes "os::unix::ffi::OsStrExt::from_bytes"
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//! [`as_bytes`]: crate::os::unix::ffi::OsStrExt::as_bytes "os::unix::ffi::OsStrExt::as_bytes"
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//! [`OsStrExt`]: crate::os::unix::ffi::OsStrExt "os::unix::ffi::OsStrExt"
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//! [windows.OsStrExt]: crate::os::windows::ffi::OsStrExt "os::windows::ffi::OsStrExt"
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//! [`encode_wide`]: crate::os::windows::ffi::OsStrExt::encode_wide "os::windows::ffi::OsStrExt::encode_wide"
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//! [`collect`]: crate::iter::Iterator::collect "iter::Iterator::collect"
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//! [windows.OsStringExt]: crate::os::windows::ffi::OsStringExt "os::windows::ffi::OsStringExt"
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//! [`from_wide`]: crate::os::windows::ffi::OsStringExt::from_wide "os::windows::ffi::OsStringExt::from_wide"
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#![stable(feature = "rust1", since = "1.0.0")]
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#[unstable(feature = "c_str_module", issue = "112134")]
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pub mod c_str;
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#[stable(feature = "core_c_void", since = "1.30.0")]
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pub use core::ffi::c_void;
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#[unstable(
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feature = "c_variadic",
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reason = "the `c_variadic` feature has not been properly tested on \
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all supported platforms",
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issue = "44930"
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)]
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pub use core::ffi::{VaList, VaListImpl};
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#[stable(feature = "core_ffi_c", since = "1.64.0")]
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pub use core::ffi::{
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c_char, c_double, c_float, c_int, c_long, c_longlong, c_schar, c_short, c_uchar, c_uint,
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c_ulong, c_ulonglong, c_ushort,
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};
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#[doc(inline)]
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#[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
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pub use self::c_str::FromBytesUntilNulError;
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#[doc(inline)]
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#[stable(feature = "cstr_from_bytes", since = "1.10.0")]
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pub use self::c_str::FromBytesWithNulError;
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#[doc(inline)]
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#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
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pub use self::c_str::FromVecWithNulError;
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#[doc(inline)]
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#[stable(feature = "cstring_into", since = "1.7.0")]
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pub use self::c_str::IntoStringError;
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#[doc(inline)]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use self::c_str::NulError;
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#[doc(inline)]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use self::c_str::{CStr, CString};
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#[stable(feature = "rust1", since = "1.0.0")]
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#[doc(inline)]
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pub use self::os_str::{OsStr, OsString};
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#[unstable(feature = "os_str_display", issue = "120048")]
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pub mod os_str;
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