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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140
#[cfg(test)]
mod tests;
use crate::borrow::{Cow, ToOwned};
use crate::boxed::Box;
use crate::rc::Rc;
use crate::slice::hack::into_vec;
use crate::string::String;
use crate::vec::Vec;
use core::borrow::Borrow;
use core::ffi::{c_char, CStr};
use core::fmt;
use core::mem;
use core::num::NonZeroU8;
use core::ops;
use core::ptr;
use core::slice;
use core::slice::memchr;
use core::str::{self, Utf8Error};
#[cfg(target_has_atomic = "ptr")]
use crate::sync::Arc;
/// A type representing an owned, C-compatible, nul-terminated string with no nul bytes in the
/// middle.
///
/// This type serves the purpose of being able to safely generate a
/// C-compatible string from a Rust byte slice or vector. An instance of this
/// type is a static guarantee that the underlying bytes contain no interior 0
/// bytes ("nul characters") and that the final byte is 0 ("nul terminator").
///
/// `CString` is to <code>&[CStr]</code> as [`String`] is to <code>&[str]</code>: the former
/// in each pair are owned strings; the latter are borrowed
/// references.
///
/// # Creating a `CString`
///
/// A `CString` is created from either a byte slice or a byte vector,
/// or anything that implements <code>[Into]<[Vec]<[u8]>></code> (for
/// example, you can build a `CString` straight out of a [`String`] or
/// a <code>&[str]</code>, since both implement that trait).
///
/// The [`CString::new`] method will actually check that the provided <code>&[[u8]]</code>
/// does not have 0 bytes in the middle, and return an error if it
/// finds one.
///
/// # Extracting a raw pointer to the whole C string
///
/// `CString` implements an [`as_ptr`][`CStr::as_ptr`] method through the [`Deref`]
/// trait. This method will give you a `*const c_char` which you can
/// feed directly to extern functions that expect a nul-terminated
/// string, like C's `strdup()`. Notice that [`as_ptr`][`CStr::as_ptr`] returns a
/// read-only pointer; if the C code writes to it, that causes
/// undefined behavior.
///
/// # Extracting a slice of the whole C string
///
/// Alternatively, you can obtain a <code>&[[u8]]</code> slice from a
/// `CString` with the [`CString::as_bytes`] method. Slices produced in this
/// way do *not* contain the trailing nul terminator. This is useful
/// when you will be calling an extern function that takes a `*const
/// u8` argument which is not necessarily nul-terminated, plus another
/// argument with the length of the string — like C's `strndup()`.
/// You can of course get the slice's length with its
/// [`len`][slice::len] method.
///
/// If you need a <code>&[[u8]]</code> slice *with* the nul terminator, you
/// can use [`CString::as_bytes_with_nul`] instead.
///
/// Once you have the kind of slice you need (with or without a nul
/// terminator), you can call the slice's own
/// [`as_ptr`][slice::as_ptr] method to get a read-only raw pointer to pass to
/// extern functions. See the documentation for that function for a
/// discussion on ensuring the lifetime of the raw pointer.
///
/// [str]: prim@str "str"
/// [`Deref`]: ops::Deref
///
/// # Examples
///
/// ```ignore (extern-declaration)
/// # fn main() {
/// use std::ffi::CString;
/// use std::os::raw::c_char;
///
/// extern "C" {
/// fn my_printer(s: *const c_char);
/// }
///
/// // We are certain that our string doesn't have 0 bytes in the middle,
/// // so we can .expect()
/// let c_to_print = CString::new("Hello, world!").expect("CString::new failed");
/// unsafe {
/// my_printer(c_to_print.as_ptr());
/// }
/// # }
/// ```
///
/// # Safety
///
/// `CString` is intended for working with traditional C-style strings
/// (a sequence of non-nul bytes terminated by a single nul byte); the
/// primary use case for these kinds of strings is interoperating with C-like
/// code. Often you will need to transfer ownership to/from that external
/// code. It is strongly recommended that you thoroughly read through the
/// documentation of `CString` before use, as improper ownership management
/// of `CString` instances can lead to invalid memory accesses, memory leaks,
/// and other memory errors.
#[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Clone)]
#[cfg_attr(not(test), rustc_diagnostic_item = "cstring_type")]
#[stable(feature = "alloc_c_string", since = "1.64.0")]
pub struct CString {
// Invariant 1: the slice ends with a zero byte and has a length of at least one.
// Invariant 2: the slice contains only one zero byte.
// Improper usage of unsafe function can break Invariant 2, but not Invariant 1.
inner: Box<[u8]>,
}
/// An error indicating that an interior nul byte was found.
///
/// While Rust strings may contain nul bytes in the middle, C strings
/// can't, as that byte would effectively truncate the string.
///
/// This error is created by the [`new`][`CString::new`] method on
/// [`CString`]. See its documentation for more.
///
/// # Examples
///
/// ```
/// use std::ffi::{CString, NulError};
///
/// let _: NulError = CString::new(b"f\0oo".to_vec()).unwrap_err();
/// ```
#[derive(Clone, PartialEq, Eq, Debug)]
#[stable(feature = "alloc_c_string", since = "1.64.0")]
pub struct NulError(usize, Vec<u8>);
#[derive(Clone, PartialEq, Eq, Debug)]
enum FromBytesWithNulErrorKind {
InteriorNul(usize),
NotNulTerminated,
}
/// An error indicating that a nul byte was not in the expected position.
///
/// The vector used to create a [`CString`] must have one and only one nul byte,
/// positioned at the end.
///
/// This error is created by the [`CString::from_vec_with_nul`] method.
/// See its documentation for more.
///
/// # Examples
///
/// ```
/// use std::ffi::{CString, FromVecWithNulError};
///
/// let _: FromVecWithNulError = CString::from_vec_with_nul(b"f\0oo".to_vec()).unwrap_err();
/// ```
#[derive(Clone, PartialEq, Eq, Debug)]
#[stable(feature = "alloc_c_string", since = "1.64.0")]
pub struct FromVecWithNulError {
error_kind: FromBytesWithNulErrorKind,
bytes: Vec<u8>,
}
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
impl FromVecWithNulError {
/// Returns a slice of [`u8`]s bytes that were attempted to convert to a [`CString`].
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::ffi::CString;
///
/// // Some invalid bytes in a vector
/// let bytes = b"f\0oo".to_vec();
///
/// let value = CString::from_vec_with_nul(bytes.clone());
///
/// assert_eq!(&bytes[..], value.unwrap_err().as_bytes());
/// ```
#[must_use]
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
pub fn as_bytes(&self) -> &[u8] {
&self.bytes[..]
}
/// Returns the bytes that were attempted to convert to a [`CString`].
///
/// This method is carefully constructed to avoid allocation. It will
/// consume the error, moving out the bytes, so that a copy of the bytes
/// does not need to be made.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::ffi::CString;
///
/// // Some invalid bytes in a vector
/// let bytes = b"f\0oo".to_vec();
///
/// let value = CString::from_vec_with_nul(bytes.clone());
///
/// assert_eq!(bytes, value.unwrap_err().into_bytes());
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
pub fn into_bytes(self) -> Vec<u8> {
self.bytes
}
}
/// An error indicating invalid UTF-8 when converting a [`CString`] into a [`String`].
///
/// `CString` is just a wrapper over a buffer of bytes with a nul terminator;
/// [`CString::into_string`] performs UTF-8 validation on those bytes and may
/// return this error.
///
/// This `struct` is created by [`CString::into_string()`]. See
/// its documentation for more.
#[derive(Clone, PartialEq, Eq, Debug)]
#[stable(feature = "alloc_c_string", since = "1.64.0")]
pub struct IntoStringError {
inner: CString,
error: Utf8Error,
}
impl CString {
/// Creates a new C-compatible string from a container of bytes.
///
/// This function will consume the provided data and use the
/// underlying bytes to construct a new string, ensuring that
/// there is a trailing 0 byte. This trailing 0 byte will be
/// appended by this function; the provided data should *not*
/// contain any 0 bytes in it.
///
/// # Examples
///
/// ```ignore (extern-declaration)
/// use std::ffi::CString;
/// use std::os::raw::c_char;
///
/// extern "C" { fn puts(s: *const c_char); }
///
/// let to_print = CString::new("Hello!").expect("CString::new failed");
/// unsafe {
/// puts(to_print.as_ptr());
/// }
/// ```
///
/// # Errors
///
/// This function will return an error if the supplied bytes contain an
/// internal 0 byte. The [`NulError`] returned will contain the bytes as well as
/// the position of the nul byte.
#[stable(feature = "rust1", since = "1.0.0")]
pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<CString, NulError> {
trait SpecNewImpl {
fn spec_new_impl(self) -> Result<CString, NulError>;
}
impl<T: Into<Vec<u8>>> SpecNewImpl for T {
default fn spec_new_impl(self) -> Result<CString, NulError> {
let bytes: Vec<u8> = self.into();
match memchr::memchr(0, &bytes) {
Some(i) => Err(NulError(i, bytes)),
None => Ok(unsafe { CString::_from_vec_unchecked(bytes) }),
}
}
}
// Specialization for avoiding reallocation
#[inline(always)] // Without that it is not inlined into specializations
fn spec_new_impl_bytes(bytes: &[u8]) -> Result<CString, NulError> {
// We cannot have such large slice that we would overflow here
// but using `checked_add` allows LLVM to assume that capacity never overflows
// and generate twice shorter code.
// `saturating_add` doesn't help for some reason.
let capacity = bytes.len().checked_add(1).unwrap();
// Allocate before validation to avoid duplication of allocation code.
// We still need to allocate and copy memory even if we get an error.
let mut buffer = Vec::with_capacity(capacity);
buffer.extend(bytes);
// Check memory of self instead of new buffer.
// This allows better optimizations if lto enabled.
match memchr::memchr(0, bytes) {
Some(i) => Err(NulError(i, buffer)),
None => Ok(unsafe { CString::_from_vec_unchecked(buffer) }),
}
}
impl SpecNewImpl for &'_ [u8] {
fn spec_new_impl(self) -> Result<CString, NulError> {
spec_new_impl_bytes(self)
}
}
impl SpecNewImpl for &'_ str {
fn spec_new_impl(self) -> Result<CString, NulError> {
spec_new_impl_bytes(self.as_bytes())
}
}
impl SpecNewImpl for &'_ mut [u8] {
fn spec_new_impl(self) -> Result<CString, NulError> {
spec_new_impl_bytes(self)
}
}
t.spec_new_impl()
}
/// Creates a C-compatible string by consuming a byte vector,
/// without checking for interior 0 bytes.
///
/// Trailing 0 byte will be appended by this function.
///
/// This method is equivalent to [`CString::new`] except that no runtime
/// assertion is made that `v` contains no 0 bytes, and it requires an
/// actual byte vector, not anything that can be converted to one with Into.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let raw = b"foo".to_vec();
/// unsafe {
/// let c_string = CString::from_vec_unchecked(raw);
/// }
/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn from_vec_unchecked(v: Vec<u8>) -> Self {
debug_assert!(memchr::memchr(0, &v).is_none());
unsafe { Self::_from_vec_unchecked(v) }
}
unsafe fn _from_vec_unchecked(mut v: Vec<u8>) -> Self {
v.reserve_exact(1);
v.push(0);
Self { inner: v.into_boxed_slice() }
}
/// Retakes ownership of a `CString` that was transferred to C via
/// [`CString::into_raw`].
///
/// Additionally, the length of the string will be recalculated from the pointer.
///
/// # Safety
///
/// This should only ever be called with a pointer that was earlier
/// obtained by calling [`CString::into_raw`]. Other usage (e.g., trying to take
/// ownership of a string that was allocated by foreign code) is likely to lead
/// to undefined behavior or allocator corruption.
///
/// It should be noted that the length isn't just "recomputed," but that
/// the recomputed length must match the original length from the
/// [`CString::into_raw`] call. This means the [`CString::into_raw`]/`from_raw`
/// methods should not be used when passing the string to C functions that can
/// modify the string's length.
///
/// > **Note:** If you need to borrow a string that was allocated by
/// > foreign code, use [`CStr`]. If you need to take ownership of
/// > a string that was allocated by foreign code, you will need to
/// > make your own provisions for freeing it appropriately, likely
/// > with the foreign code's API to do that.
///
/// # Examples
///
/// Creates a `CString`, pass ownership to an `extern` function (via raw pointer), then retake
/// ownership with `from_raw`:
///
/// ```ignore (extern-declaration)
/// use std::ffi::CString;
/// use std::os::raw::c_char;
///
/// extern "C" {
/// fn some_extern_function(s: *mut c_char);
/// }
///
/// let c_string = CString::new("Hello!").expect("CString::new failed");
/// let raw = c_string.into_raw();
/// unsafe {
/// some_extern_function(raw);
/// let c_string = CString::from_raw(raw);
/// }
/// ```
#[must_use = "call `drop(from_raw(ptr))` if you intend to drop the `CString`"]
#[stable(feature = "cstr_memory", since = "1.4.0")]
pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
// SAFETY: This is called with a pointer that was obtained from a call
// to `CString::into_raw` and the length has not been modified. As such,
// we know there is a NUL byte (and only one) at the end and that the
// information about the size of the allocation is correct on Rust's
// side.
unsafe {
extern "C" {
/// Provided by libc or compiler_builtins.
fn strlen(s: *const c_char) -> usize;
}
let len = strlen(ptr) + 1; // Including the NUL byte
let slice = slice::from_raw_parts_mut(ptr, len as usize);
CString { inner: Box::from_raw(slice as *mut [c_char] as *mut [u8]) }
}
}
/// Consumes the `CString` and transfers ownership of the string to a C caller.
///
/// The pointer which this function returns must be returned to Rust and reconstituted using
/// [`CString::from_raw`] to be properly deallocated. Specifically, one
/// should *not* use the standard C `free()` function to deallocate
/// this string.
///
/// Failure to call [`CString::from_raw`] will lead to a memory leak.
///
/// The C side must **not** modify the length of the string (by writing a
/// nul byte somewhere inside the string or removing the final one) before
/// it makes it back into Rust using [`CString::from_raw`]. See the safety section
/// in [`CString::from_raw`].
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let c_string = CString::new("foo").expect("CString::new failed");
///
/// let ptr = c_string.into_raw();
///
/// unsafe {
/// assert_eq!(b'f', *ptr as u8);
/// assert_eq!(b'o', *ptr.add(1) as u8);
/// assert_eq!(b'o', *ptr.add(2) as u8);
/// assert_eq!(b'\0', *ptr.add(3) as u8);
///
/// // retake pointer to free memory
/// let _ = CString::from_raw(ptr);
/// }
/// ```
#[inline]
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstr_memory", since = "1.4.0")]
pub fn into_raw(self) -> *mut c_char {
Box::into_raw(self.into_inner()) as *mut c_char
}
/// Converts the `CString` into a [`String`] if it contains valid UTF-8 data.
///
/// On failure, ownership of the original `CString` is returned.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let valid_utf8 = vec![b'f', b'o', b'o'];
/// let cstring = CString::new(valid_utf8).expect("CString::new failed");
/// assert_eq!(cstring.into_string().expect("into_string() call failed"), "foo");
///
/// let invalid_utf8 = vec![b'f', 0xff, b'o', b'o'];
/// let cstring = CString::new(invalid_utf8).expect("CString::new failed");
/// let err = cstring.into_string().err().expect("into_string().err() failed");
/// assert_eq!(err.utf8_error().valid_up_to(), 1);
/// ```
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn into_string(self) -> Result<String, IntoStringError> {
String::from_utf8(self.into_bytes()).map_err(|e| IntoStringError {
error: e.utf8_error(),
inner: unsafe { Self::_from_vec_unchecked(e.into_bytes()) },
})
}
/// Consumes the `CString` and returns the underlying byte buffer.
///
/// The returned buffer does **not** contain the trailing nul
/// terminator, and it is guaranteed to not have any interior nul
/// bytes.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let c_string = CString::new("foo").expect("CString::new failed");
/// let bytes = c_string.into_bytes();
/// assert_eq!(bytes, vec![b'f', b'o', b'o']);
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn into_bytes(self) -> Vec<u8> {
let mut vec = into_vec(self.into_inner());
let _nul = vec.pop();
debug_assert_eq!(_nul, Some(0u8));
vec
}
/// Equivalent to [`CString::into_bytes()`] except that the
/// returned vector includes the trailing nul terminator.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let c_string = CString::new("foo").expect("CString::new failed");
/// let bytes = c_string.into_bytes_with_nul();
/// assert_eq!(bytes, vec![b'f', b'o', b'o', b'\0']);
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn into_bytes_with_nul(self) -> Vec<u8> {
into_vec(self.into_inner())
}
/// Returns the contents of this `CString` as a slice of bytes.
///
/// The returned slice does **not** contain the trailing nul
/// terminator, and it is guaranteed to not have any interior nul
/// bytes. If you need the nul terminator, use
/// [`CString::as_bytes_with_nul`] instead.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let c_string = CString::new("foo").expect("CString::new failed");
/// let bytes = c_string.as_bytes();
/// assert_eq!(bytes, &[b'f', b'o', b'o']);
/// ```
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn as_bytes(&self) -> &[u8] {
// SAFETY: CString has a length at least 1
unsafe { self.inner.get_unchecked(..self.inner.len() - 1) }
}
/// Equivalent to [`CString::as_bytes()`] except that the
/// returned slice includes the trailing nul terminator.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let c_string = CString::new("foo").expect("CString::new failed");
/// let bytes = c_string.as_bytes_with_nul();
/// assert_eq!(bytes, &[b'f', b'o', b'o', b'\0']);
/// ```
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn as_bytes_with_nul(&self) -> &[u8] {
&self.inner
}
/// Extracts a [`CStr`] slice containing the entire string.
///
/// # Examples
///
/// ```
/// use std::ffi::{CString, CStr};
///
/// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
/// let cstr = c_string.as_c_str();
/// assert_eq!(cstr,
/// CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"));
/// ```
#[inline]
#[must_use]
#[stable(feature = "as_c_str", since = "1.20.0")]
pub fn as_c_str(&self) -> &CStr {
&*self
}
/// Converts this `CString` into a boxed [`CStr`].
///
/// # Examples
///
/// ```
/// use std::ffi::{CString, CStr};
///
/// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
/// let boxed = c_string.into_boxed_c_str();
/// assert_eq!(&*boxed,
/// CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"));
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "into_boxed_c_str", since = "1.20.0")]
pub fn into_boxed_c_str(self) -> Box<CStr> {
unsafe { Box::from_raw(Box::into_raw(self.into_inner()) as *mut CStr) }
}
/// Bypass "move out of struct which implements [`Drop`] trait" restriction.
#[inline]
fn into_inner(self) -> Box<[u8]> {
// Rationale: `mem::forget(self)` invalidates the previous call to `ptr::read(&self.inner)`
// so we use `ManuallyDrop` to ensure `self` is not dropped.
// Then we can return the box directly without invalidating it.
// See https://github.com/rust-lang/rust/issues/62553.
let this = mem::ManuallyDrop::new(self);
unsafe { ptr::read(&this.inner) }
}
/// Converts a <code>[Vec]<[u8]></code> to a [`CString`] without checking the
/// invariants on the given [`Vec`].
///
/// # Safety
///
/// The given [`Vec`] **must** have one nul byte as its last element.
/// This means it cannot be empty nor have any other nul byte anywhere else.
///
/// # Example
///
/// ```
/// use std::ffi::CString;
/// assert_eq!(
/// unsafe { CString::from_vec_with_nul_unchecked(b"abc\0".to_vec()) },
/// unsafe { CString::from_vec_unchecked(b"abc".to_vec()) }
/// );
/// ```
#[must_use]
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
pub unsafe fn from_vec_with_nul_unchecked(v: Vec<u8>) -> Self {
debug_assert!(memchr::memchr(0, &v).unwrap() + 1 == v.len());
unsafe { Self::_from_vec_with_nul_unchecked(v) }
}
unsafe fn _from_vec_with_nul_unchecked(v: Vec<u8>) -> Self {
Self { inner: v.into_boxed_slice() }
}
/// Attempts to converts a <code>[Vec]<[u8]></code> to a [`CString`].
///
/// Runtime checks are present to ensure there is only one nul byte in the
/// [`Vec`], its last element.
///
/// # Errors
///
/// If a nul byte is present and not the last element or no nul bytes
/// is present, an error will be returned.
///
/// # Examples
///
/// A successful conversion will produce the same result as [`CString::new`]
/// when called without the ending nul byte.
///
/// ```
/// use std::ffi::CString;
/// assert_eq!(
/// CString::from_vec_with_nul(b"abc\0".to_vec())
/// .expect("CString::from_vec_with_nul failed"),
/// CString::new(b"abc".to_vec()).expect("CString::new failed")
/// );
/// ```
///
/// An incorrectly formatted [`Vec`] will produce an error.
///
/// ```
/// use std::ffi::{CString, FromVecWithNulError};
/// // Interior nul byte
/// let _: FromVecWithNulError = CString::from_vec_with_nul(b"a\0bc".to_vec()).unwrap_err();
/// // No nul byte
/// let _: FromVecWithNulError = CString::from_vec_with_nul(b"abc".to_vec()).unwrap_err();
/// ```
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
pub fn from_vec_with_nul(v: Vec<u8>) -> Result<Self, FromVecWithNulError> {
let nul_pos = memchr::memchr(0, &v);
match nul_pos {
Some(nul_pos) if nul_pos + 1 == v.len() => {
// SAFETY: We know there is only one nul byte, at the end
// of the vec.
Ok(unsafe { Self::_from_vec_with_nul_unchecked(v) })
}
Some(nul_pos) => Err(FromVecWithNulError {
error_kind: FromBytesWithNulErrorKind::InteriorNul(nul_pos),
bytes: v,
}),
None => Err(FromVecWithNulError {
error_kind: FromBytesWithNulErrorKind::NotNulTerminated,
bytes: v,
}),
}
}
}
// Turns this `CString` into an empty string to prevent
// memory-unsafe code from working by accident. Inline
// to prevent LLVM from optimizing it away in debug builds.
#[stable(feature = "cstring_drop", since = "1.13.0")]
impl Drop for CString {
#[inline]
fn drop(&mut self) {
unsafe {
*self.inner.get_unchecked_mut(0) = 0;
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl ops::Deref for CString {
type Target = CStr;
#[inline]
fn deref(&self) -> &CStr {
unsafe { CStr::from_bytes_with_nul_unchecked(self.as_bytes_with_nul()) }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Debug for CString {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&**self, f)
}
}
#[stable(feature = "cstring_into", since = "1.7.0")]
impl From<CString> for Vec<u8> {
/// Converts a [`CString`] into a <code>[Vec]<[u8]></code>.
///
/// The conversion consumes the [`CString`], and removes the terminating NUL byte.
#[inline]
fn from(s: CString) -> Vec<u8> {
s.into_bytes()
}
}
#[stable(feature = "cstr_default", since = "1.10.0")]
impl Default for CString {
/// Creates an empty `CString`.
fn default() -> CString {
let a: &CStr = Default::default();
a.to_owned()
}
}
#[stable(feature = "cstr_borrow", since = "1.3.0")]
impl Borrow<CStr> for CString {
#[inline]
fn borrow(&self) -> &CStr {
self
}
}
#[stable(feature = "cstring_from_cow_cstr", since = "1.28.0")]
impl<'a> From<Cow<'a, CStr>> for CString {
/// Converts a `Cow<'a, CStr>` into a `CString`, by copying the contents if they are
/// borrowed.
#[inline]
fn from(s: Cow<'a, CStr>) -> Self {
s.into_owned()
}
}
#[cfg(not(test))]
#[stable(feature = "box_from_c_str", since = "1.17.0")]
impl From<&CStr> for Box<CStr> {
/// Converts a `&CStr` into a `Box<CStr>`,
/// by copying the contents into a newly allocated [`Box`].
fn from(s: &CStr) -> Box<CStr> {
let boxed: Box<[u8]> = Box::from(s.to_bytes_with_nul());
unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
}
}
#[stable(feature = "box_from_cow", since = "1.45.0")]
impl From<Cow<'_, CStr>> for Box<CStr> {
/// Converts a `Cow<'a, CStr>` into a `Box<CStr>`,
/// by copying the contents if they are borrowed.
#[inline]
fn from(cow: Cow<'_, CStr>) -> Box<CStr> {
match cow {
Cow::Borrowed(s) => Box::from(s),
Cow::Owned(s) => Box::from(s),
}
}
}
#[stable(feature = "c_string_from_box", since = "1.18.0")]
impl From<Box<CStr>> for CString {
/// Converts a <code>[Box]<[CStr]></code> into a [`CString`] without copying or allocating.
#[inline]
fn from(s: Box<CStr>) -> CString {
let raw = Box::into_raw(s) as *mut [u8];
CString { inner: unsafe { Box::from_raw(raw) } }
}
}
#[stable(feature = "cstring_from_vec_of_nonzerou8", since = "1.43.0")]
impl From<Vec<NonZeroU8>> for CString {
/// Converts a <code>[Vec]<[NonZeroU8]></code> into a [`CString`] without
/// copying nor checking for inner nul bytes.
#[inline]
fn from(v: Vec<NonZeroU8>) -> CString {
unsafe {
// Transmute `Vec<NonZeroU8>` to `Vec<u8>`.
let v: Vec<u8> = {
// SAFETY:
// - transmuting between `NonZeroU8` and `u8` is sound;
// - `alloc::Layout<NonZeroU8> == alloc::Layout<u8>`.
let (ptr, len, cap): (*mut NonZeroU8, _, _) = Vec::into_raw_parts(v);
Vec::from_raw_parts(ptr.cast::<u8>(), len, cap)
};
// SAFETY: `v` cannot contain nul bytes, given the type-level
// invariant of `NonZeroU8`.
Self::_from_vec_unchecked(v)
}
}
}
#[cfg(not(test))]
#[stable(feature = "more_box_slice_clone", since = "1.29.0")]
impl Clone for Box<CStr> {
#[inline]
fn clone(&self) -> Self {
(**self).into()
}
}
#[stable(feature = "box_from_c_string", since = "1.20.0")]
impl From<CString> for Box<CStr> {
/// Converts a [`CString`] into a <code>[Box]<[CStr]></code> without copying or allocating.
#[inline]
fn from(s: CString) -> Box<CStr> {
s.into_boxed_c_str()
}
}
#[stable(feature = "cow_from_cstr", since = "1.28.0")]
impl<'a> From<CString> for Cow<'a, CStr> {
/// Converts a [`CString`] into an owned [`Cow`] without copying or allocating.
#[inline]
fn from(s: CString) -> Cow<'a, CStr> {
Cow::Owned(s)
}
}
#[stable(feature = "cow_from_cstr", since = "1.28.0")]
impl<'a> From<&'a CStr> for Cow<'a, CStr> {
/// Converts a [`CStr`] into a borrowed [`Cow`] without copying or allocating.
#[inline]
fn from(s: &'a CStr) -> Cow<'a, CStr> {
Cow::Borrowed(s)
}
}
#[stable(feature = "cow_from_cstr", since = "1.28.0")]
impl<'a> From<&'a CString> for Cow<'a, CStr> {
/// Converts a `&`[`CString`] into a borrowed [`Cow`] without copying or allocating.
#[inline]
fn from(s: &'a CString) -> Cow<'a, CStr> {
Cow::Borrowed(s.as_c_str())
}
}
#[cfg(target_has_atomic = "ptr")]
#[stable(feature = "shared_from_slice2", since = "1.24.0")]
impl From<CString> for Arc<CStr> {
/// Converts a [`CString`] into an <code>[Arc]<[CStr]></code> by moving the [`CString`]
/// data into a new [`Arc`] buffer.
#[inline]
fn from(s: CString) -> Arc<CStr> {
let arc: Arc<[u8]> = Arc::from(s.into_inner());
unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
}
}
#[cfg(target_has_atomic = "ptr")]
#[stable(feature = "shared_from_slice2", since = "1.24.0")]
impl From<&CStr> for Arc<CStr> {
/// Converts a `&CStr` into a `Arc<CStr>`,
/// by copying the contents into a newly allocated [`Arc`].
#[inline]
fn from(s: &CStr) -> Arc<CStr> {
let arc: Arc<[u8]> = Arc::from(s.to_bytes_with_nul());
unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
}
}
#[stable(feature = "shared_from_slice2", since = "1.24.0")]
impl From<CString> for Rc<CStr> {
/// Converts a [`CString`] into an <code>[Rc]<[CStr]></code> by moving the [`CString`]
/// data into a new [`Rc`] buffer.
#[inline]
fn from(s: CString) -> Rc<CStr> {
let rc: Rc<[u8]> = Rc::from(s.into_inner());
unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
}
}
#[stable(feature = "shared_from_slice2", since = "1.24.0")]
impl From<&CStr> for Rc<CStr> {
/// Converts a `&CStr` into a `Rc<CStr>`,
/// by copying the contents into a newly allocated [`Rc`].
#[inline]
fn from(s: &CStr) -> Rc<CStr> {
let rc: Rc<[u8]> = Rc::from(s.to_bytes_with_nul());
unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
}
}
#[cfg(not(test))]
#[stable(feature = "default_box_extra", since = "1.17.0")]
impl Default for Box<CStr> {
fn default() -> Box<CStr> {
let boxed: Box<[u8]> = Box::from([0]);
unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
}
}
impl NulError {
/// Returns the position of the nul byte in the slice that caused
/// [`CString::new`] to fail.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let nul_error = CString::new("foo\0bar").unwrap_err();
/// assert_eq!(nul_error.nul_position(), 3);
///
/// let nul_error = CString::new("foo bar\0").unwrap_err();
/// assert_eq!(nul_error.nul_position(), 7);
/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn nul_position(&self) -> usize {
self.0
}
/// Consumes this error, returning the underlying vector of bytes which
/// generated the error in the first place.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let nul_error = CString::new("foo\0bar").unwrap_err();
/// assert_eq!(nul_error.into_vec(), b"foo\0bar");
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn into_vec(self) -> Vec<u8> {
self.1
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for NulError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "nul byte found in provided data at position: {}", self.0)
}
}
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
impl fmt::Display for FromVecWithNulError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self.error_kind {
FromBytesWithNulErrorKind::InteriorNul(pos) => {
write!(f, "data provided contains an interior nul byte at pos {pos}")
}
FromBytesWithNulErrorKind::NotNulTerminated => {
write!(f, "data provided is not nul terminated")
}
}
}
}
impl IntoStringError {
/// Consumes this error, returning original [`CString`] which generated the
/// error.
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn into_cstring(self) -> CString {
self.inner
}
/// Access the underlying UTF-8 error that was the cause of this error.
#[must_use]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn utf8_error(&self) -> Utf8Error {
self.error
}
}
impl IntoStringError {
fn description(&self) -> &str {
"C string contained non-utf8 bytes"
}
}
#[stable(feature = "cstring_into", since = "1.7.0")]
impl fmt::Display for IntoStringError {
#[allow(deprecated, deprecated_in_future)]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.description().fmt(f)
}
}
#[stable(feature = "cstr_borrow", since = "1.3.0")]
impl ToOwned for CStr {
type Owned = CString;
fn to_owned(&self) -> CString {
CString { inner: self.to_bytes_with_nul().into() }
}
fn clone_into(&self, target: &mut CString) {
let mut b = into_vec(mem::take(&mut target.inner));
self.to_bytes_with_nul().clone_into(&mut b);
target.inner = b.into_boxed_slice();
}
}
#[stable(feature = "cstring_asref", since = "1.7.0")]
impl From<&CStr> for CString {
fn from(s: &CStr) -> CString {
s.to_owned()
}
}
#[stable(feature = "cstring_asref", since = "1.7.0")]
impl ops::Index<ops::RangeFull> for CString {
type Output = CStr;
#[inline]
fn index(&self, _index: ops::RangeFull) -> &CStr {
self
}
}
#[stable(feature = "cstring_asref", since = "1.7.0")]
impl AsRef<CStr> for CString {
#[inline]
fn as_ref(&self) -> &CStr {
self
}
}
#[cfg(not(test))]
impl CStr {
/// Converts a `CStr` into a <code>[Cow]<[str]></code>.
///
/// If the contents of the `CStr` are valid UTF-8 data, this
/// function will return a <code>[Cow]::[Borrowed]\(&[str])</code>
/// with the corresponding <code>&[str]</code> slice. Otherwise, it will
/// replace any invalid UTF-8 sequences with
/// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD] and return a
/// <code>[Cow]::[Owned]\(&[str])</code> with the result.
///
/// [str]: prim@str "str"
/// [Borrowed]: Cow::Borrowed
/// [Owned]: Cow::Owned
/// [U+FFFD]: core::char::REPLACEMENT_CHARACTER "std::char::REPLACEMENT_CHARACTER"
///
/// # Examples
///
/// Calling `to_string_lossy` on a `CStr` containing valid UTF-8:
///
/// ```
/// use std::borrow::Cow;
/// use std::ffi::CStr;
///
/// let cstr = CStr::from_bytes_with_nul(b"Hello World\0")
/// .expect("CStr::from_bytes_with_nul failed");
/// assert_eq!(cstr.to_string_lossy(), Cow::Borrowed("Hello World"));
/// ```
///
/// Calling `to_string_lossy` on a `CStr` containing invalid UTF-8:
///
/// ```
/// use std::borrow::Cow;
/// use std::ffi::CStr;
///
/// let cstr = CStr::from_bytes_with_nul(b"Hello \xF0\x90\x80World\0")
/// .expect("CStr::from_bytes_with_nul failed");
/// assert_eq!(
/// cstr.to_string_lossy(),
/// Cow::Owned(String::from("Hello �World")) as Cow<'_, str>
/// );
/// ```
#[rustc_allow_incoherent_impl]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[stable(feature = "cstr_to_str", since = "1.4.0")]
pub fn to_string_lossy(&self) -> Cow<'_, str> {
String::from_utf8_lossy(self.to_bytes())
}
/// Converts a <code>[Box]<[CStr]></code> into a [`CString`] without copying or allocating.
///
/// # Examples
///
/// ```
/// use std::ffi::CString;
///
/// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed");
/// let boxed = c_string.into_boxed_c_str();
/// assert_eq!(boxed.into_c_string(), CString::new("foo").expect("CString::new failed"));
/// ```
#[rustc_allow_incoherent_impl]
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "into_boxed_c_str", since = "1.20.0")]
pub fn into_c_string(self: Box<Self>) -> CString {
CString::from(self)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl core::error::Error for NulError {
#[allow(deprecated)]
fn description(&self) -> &str {
"nul byte found in data"
}
}
#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
impl core::error::Error for FromVecWithNulError {}
#[stable(feature = "cstring_into", since = "1.7.0")]
impl core::error::Error for IntoStringError {
#[allow(deprecated)]
fn description(&self) -> &str {
"C string contained non-utf8 bytes"
}
fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
Some(&self.error)
}
}