1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205
//! 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 an *O*(1) operation (because the
//! length is stored); in C it is an *O*(*n*) 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 <code>\*mut [u8]</code> 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 <code>\*const [u8]</code> 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
//! <code>&[str]</code> 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`] losslessly represents an owned platform string. However, this
//! representation is not necessarily in a form native to the platform.
//! 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 <code>[Option]<[OsString]></code>. If the environment variable
//! exists you will get a <code>[Some]\(os_string)</code>, 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`] losslessly represents a borrowed reference to a platform string.
//! However, this representation is not necessarily in a form native to the platform.
//! It can be converted into a UTF-8 Rust string slice in a similar way to
//! [`OsString`].
//!
//! # Conversions
//!
//! ## On Unix
//!
//! On Unix, [`OsStr`] implements the
//! <code>std::os::unix::ffi::[OsStrExt][unix.OsStrExt]</code> trait, which
//! augments it with two methods, [`from_bytes`] and [`as_bytes`].
//! These do inexpensive conversions from and to byte slices.
//!
//! Additionally, on Unix [`OsString`] implements the
//! <code>std::os::unix::ffi::[OsStringExt][unix.OsStringExt]</code> trait,
//! which provides [`from_vec`] and [`into_vec`] methods that consume
//! their arguments, and take or produce vectors of [`u8`].
//!
//! ## On Windows
//!
//! An [`OsStr`] can be losslessly converted to a native Windows string. And
//! a native Windows string can be losslessly converted to an [`OsString`].
//!
//! On Windows, [`OsStr`] implements the
//! <code>std::os::windows::ffi::[OsStrExt][windows.OsStrExt]</code> trait,
//! which provides an [`encode_wide`] method. This provides an
//! iterator that can be [`collect`]ed into a vector of [`u16`]. After a nul
//! characters is appended, this is the same as a native Windows string.
//!
//! Additionally, on Windows [`OsString`] implements the
//! <code>std::os::windows:ffi::[OsStringExt][windows.OsStringExt]</code>
//! trait, which provides a [`from_wide`] method to convert a native Windows
//! string (without the terminating nul character) to an [`OsString`].
//!
//! ## Other platforms
//!
//! Many other platforms provide their own extension traits in a
//! `std::os::*::ffi` module.
//!
//! ## On all platforms
//!
//! On all platforms, [`OsStr`] consists of a sequence of bytes that is encoded as a superset of
//! UTF-8; see [`OsString`] for more details on its encoding on different platforms.
//!
//! For limited, inexpensive conversions from and to bytes, see [`OsStr::as_encoded_bytes`] and
//! [`OsStr::from_encoded_bytes_unchecked`].
//!
//! For basic string processing, see [`OsStr::slice_encoded_bytes`].
//!
//! [Unicode scalar value]: https://www.unicode.org/glossary/#unicode_scalar_value
//! [Unicode code point]: https://www.unicode.org/glossary/#code_point
//! [`env::set_var()`]: crate::env::set_var "env::set_var"
//! [`env::var_os()`]: crate::env::var_os "env::var_os"
//! [unix.OsStringExt]: crate::os::unix::ffi::OsStringExt "os::unix::ffi::OsStringExt"
//! [`from_vec`]: crate::os::unix::ffi::OsStringExt::from_vec "os::unix::ffi::OsStringExt::from_vec"
//! [`into_vec`]: crate::os::unix::ffi::OsStringExt::into_vec "os::unix::ffi::OsStringExt::into_vec"
//! [unix.OsStrExt]: crate::os::unix::ffi::OsStrExt "os::unix::ffi::OsStrExt"
//! [`from_bytes`]: crate::os::unix::ffi::OsStrExt::from_bytes "os::unix::ffi::OsStrExt::from_bytes"
//! [`as_bytes`]: crate::os::unix::ffi::OsStrExt::as_bytes "os::unix::ffi::OsStrExt::as_bytes"
//! [`OsStrExt`]: crate::os::unix::ffi::OsStrExt "os::unix::ffi::OsStrExt"
//! [windows.OsStrExt]: crate::os::windows::ffi::OsStrExt "os::windows::ffi::OsStrExt"
//! [`encode_wide`]: crate::os::windows::ffi::OsStrExt::encode_wide "os::windows::ffi::OsStrExt::encode_wide"
//! [`collect`]: crate::iter::Iterator::collect "iter::Iterator::collect"
//! [windows.OsStringExt]: crate::os::windows::ffi::OsStringExt "os::windows::ffi::OsStringExt"
//! [`from_wide`]: crate::os::windows::ffi::OsStringExt::from_wide "os::windows::ffi::OsStringExt::from_wide"
#![stable(feature = "rust1", since = "1.0.0")]
#[unstable(feature = "c_str_module", issue = "112134")]
pub mod c_str;
#[stable(feature = "core_c_void", since = "1.30.0")]
pub use core::ffi::c_void;
#[stable(feature = "core_ffi_c", since = "1.64.0")]
pub use core::ffi::{
c_char, c_double, c_float, c_int, c_long, c_longlong, c_schar, c_short, c_uchar, c_uint,
c_ulong, c_ulonglong, c_ushort,
};
#[unstable(
feature = "c_variadic",
reason = "the `c_variadic` feature has not been properly tested on \
all supported platforms",
issue = "44930"
)]
pub use core::ffi::{VaList, VaListImpl};
#[doc(no_inline)]
#[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
pub use self::c_str::FromBytesUntilNulError;
#[doc(no_inline)]
#[stable(feature = "cstr_from_bytes", since = "1.10.0")]
pub use self::c_str::FromBytesWithNulError;
#[doc(no_inline)]
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
pub use self::c_str::FromVecWithNulError;
#[doc(no_inline)]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub use self::c_str::IntoStringError;
#[doc(no_inline)]
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::c_str::NulError;
#[doc(inline)]
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::c_str::{CStr, CString};
#[stable(feature = "rust1", since = "1.0.0")]
#[doc(inline)]
pub use self::os_str::{OsStr, OsString};
#[unstable(feature = "os_str_display", issue = "120048")]
pub mod os_str;