1.0.0[−][src]Struct std::ffi::CStr
Representation of a borrowed C string.
This type represents a borrowed reference to a nul-terminated
array of bytes. It can be constructed safely from a &[
u8
]
slice, or unsafely from a raw *const c_char
. It can then be
converted to a Rust &str
by performing UTF-8 validation, or
into an owned CString
.
&CStr
is to CString
as &str
is to String
: the former
in each pair are borrowed references; the latter are owned
strings.
Note that this structure is not repr(C)
and is not recommended to be
placed in the signatures of FFI functions. Instead, safe wrappers of FFI
functions may leverage the unsafe from_ptr
constructor to provide a safe
interface to other consumers.
Examples
Inspecting a foreign C string:
use std::ffi::CStr; use std::os::raw::c_char; extern { fn my_string() -> *const c_char; } unsafe { let slice = CStr::from_ptr(my_string()); println!("string buffer size without nul terminator: {}", slice.to_bytes().len()); }Run
Passing a Rust-originating C string:
use std::ffi::{CString, CStr}; use std::os::raw::c_char; fn work(data: &CStr) { extern { fn work_with(data: *const c_char); } unsafe { work_with(data.as_ptr()) } } let s = CString::new("data data data data").expect("CString::new failed"); work(&s);Run
Converting a foreign C string into a Rust String
:
use std::ffi::CStr; use std::os::raw::c_char; extern { fn my_string() -> *const c_char; } fn my_string_safe() -> String { unsafe { CStr::from_ptr(my_string()).to_string_lossy().into_owned() } } println!("string: {}", my_string_safe());Run
Methods
impl CStr
[src]
pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr
[src]
Wraps a raw C string with a safe C string wrapper.
This function will wrap the provided ptr
with a CStr
wrapper, which
allows inspection and interoperation of non-owned C strings. The total
size of the raw C string must be smaller than isize::MAX
bytes
in memory due to calling the slice::from_raw_parts
function.
This method is unsafe for a number of reasons:
- There is no guarantee to the validity of
ptr
. - The returned lifetime is not guaranteed to be the actual lifetime of
ptr
. - There is no guarantee that the memory pointed to by
ptr
contains a valid nul terminator byte at the end of the string. - It is not guaranteed that the memory pointed by
ptr
won't change before theCStr
has been destroyed.
Note: This operation is intended to be a 0-cost cast but it is currently implemented with an up-front calculation of the length of the string. This is not guaranteed to always be the case.
Examples
use std::ffi::CStr; use std::os::raw::c_char; extern { fn my_string() -> *const c_char; } unsafe { let slice = CStr::from_ptr(my_string()); println!("string returned: {}", slice.to_str().unwrap()); }Run
pub fn from_bytes_with_nul(bytes: &[u8]) -> Result<&CStr, FromBytesWithNulError>
1.10.0[src]
Creates a C string wrapper from a byte slice.
This function will cast the provided bytes
to a CStr
wrapper after ensuring that the byte slice is nul-terminated
and does not contain any interior nul bytes.
Examples
use std::ffi::CStr; let cstr = CStr::from_bytes_with_nul(b"hello\0"); assert!(cstr.is_ok());Run
Creating a CStr
without a trailing nul terminator is an error:
use std::ffi::CStr; let cstr = CStr::from_bytes_with_nul(b"hello"); assert!(cstr.is_err());Run
Creating a CStr
with an interior nul byte is an error:
use std::ffi::CStr; let cstr = CStr::from_bytes_with_nul(b"he\0llo\0"); assert!(cstr.is_err());Run
pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr
1.10.0[src]
Unsafely creates a C string wrapper from a byte slice.
This function will cast the provided bytes
to a CStr
wrapper without
performing any sanity checks. The provided slice must be nul-terminated
and not contain any interior nul bytes.
Examples
use std::ffi::{CStr, CString}; unsafe { let cstring = CString::new("hello").expect("CString::new failed"); let cstr = CStr::from_bytes_with_nul_unchecked(cstring.to_bytes_with_nul()); assert_eq!(cstr, &*cstring); }Run
pub const fn as_ptr(&self) -> *const c_char
[src]
Returns the inner pointer to this C string.
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.
WARNING
The returned pointer is read-only; writing to it (including passing it to C code that writes to it) causes undefined behavior.
It is your responsibility to make sure that the underlying memory is not
freed too early. For example, the following code will cause undefined
behavior when ptr
is used inside the unsafe
block:
use std::ffi::CString; let ptr = CString::new("Hello").expect("CString::new failed").as_ptr(); unsafe { // `ptr` is dangling *ptr; }Run
This happens because the pointer returned by as_ptr
does not carry any
lifetime information and the CString
is deallocated immediately after
the CString::new("Hello").expect("CString::new failed").as_ptr()
expression is evaluated.
To fix the problem, bind the CString
to a local variable:
use std::ffi::CString; let hello = CString::new("Hello").expect("CString::new failed"); let ptr = hello.as_ptr(); unsafe { // `ptr` is valid because `hello` is in scope *ptr; }Run
This way, the lifetime of the CString
in hello
encompasses
the lifetime of ptr
and the unsafe
block.
pub fn to_bytes(&self) -> &[u8]
[src]
Converts this C string to a byte slice.
The returned slice will not contain the trailing nul terminator that this C string has.
Note: This method is currently implemented as a constant-time cast, but it is planned to alter its definition in the future to perform the length calculation whenever this method is called.
Examples
use std::ffi::CStr; let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"); assert_eq!(cstr.to_bytes(), b"foo");Run
pub fn to_bytes_with_nul(&self) -> &[u8]
[src]
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 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 length calculation whenever this method is called.
Examples
use std::ffi::CStr; let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"); assert_eq!(cstr.to_bytes_with_nul(), b"foo\0");Run
pub fn to_str(&self) -> Result<&str, Utf8Error>
1.4.0[src]
Yields a &str
slice if the CStr
contains valid UTF-8.
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 constant-time cast, but it is planned to alter its definition in the future to perform the length calculation in addition to the UTF-8 check whenever this method is called.
Examples
use std::ffi::CStr; let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"); assert_eq!(cstr.to_str(), Ok("foo"));Run
pub fn to_string_lossy(&self) -> Cow<str>
1.4.0[src]
Converts a CStr
into a Cow
<
str
>
.
If the contents of the CStr
are valid UTF-8 data, this
function will return a Cow
::
Borrowed
(
[&str
])
with 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 constant-time cast, but it is planned to alter its definition in the future to perform the length calculation in addition to the UTF-8 check whenever this method is called.
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"));Run
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> );Run
pub fn into_c_string(self: Box<CStr>) -> CString
1.20.0[src]
Converts a Box
<CStr>
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"));Run
Trait Implementations
impl<'_> From<&'_ CStr> for Box<CStr>
1.17.0[src]
impl<'a> From<&'a CStr> for Cow<'a, CStr>
1.28.0[src]
impl<'_> From<&'_ CStr> for Arc<CStr>
1.24.0[src]
impl<'_> From<&'_ CStr> for Rc<CStr>
1.24.0[src]
impl<'_> From<&'_ CStr> for CString
1.7.0[src]
impl PartialEq<CStr> for CStr
[src]
impl Eq for CStr
[src]
impl Ord for CStr
[src]
fn cmp(&self, other: &CStr) -> Ordering
[src]
fn max(self, other: Self) -> Self
1.21.0[src]
fn min(self, other: Self) -> Self
1.21.0[src]
fn clamp(self, min: Self, max: Self) -> Self
[src]
impl PartialOrd<CStr> for CStr
[src]
fn partial_cmp(&self, other: &CStr) -> Option<Ordering>
[src]
#[must_use]
fn lt(&self, other: &Rhs) -> bool
[src]
#[must_use]
fn le(&self, other: &Rhs) -> bool
[src]
#[must_use]
fn gt(&self, other: &Rhs) -> bool
[src]
#[must_use]
fn ge(&self, other: &Rhs) -> bool
[src]
impl Hash for CStr
[src]
fn hash<__H: Hasher>(&self, state: &mut __H)
[src]
fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,
1.3.0[src]
H: Hasher,