Struct drone_core::ffi::CStr [−][src]
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 CStr::from_ptr
constructor to provide
a safe interface to other consumers.
Examples
Inspecting a foreign C string:
use drone_core::ffi::{c_char, CStr}; extern "C" fn my_string() -> *const c_char { "example".as_ptr() } unsafe { let slice = CStr::from_ptr(my_string()); println!("string buffer size without nul terminator: {}", slice.to_bytes().len(),); }
Passing a Rust-originating C string:
use drone_core::ffi::{c_char, CStr, CString}; fn work(data: &CStr) { extern "C" 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);
Converting a foreign C string into a Rust String
:
use drone_core::ffi::{c_char, CStr}; extern "C" fn my_string() -> *const c_char { "example".as_ptr() } fn my_string_safe() -> String { unsafe { CStr::from_ptr(my_string()).to_string_lossy().into_owned() } } println!("string: {}", my_string_safe());
Implementations
impl CStr
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pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a Self
[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. 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 drone_core::ffi::{c_char, CStr}; extern "C" fn my_string() -> *const c_char { "example\0".as_ptr() } unsafe { let slice = CStr::from_ptr(my_string()); println!("string returned: {}", slice.to_str().unwrap()); }
pub fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, FromBytesWithNulError>
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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 drone_core::ffi::CStr; let cstr = CStr::from_bytes_with_nul(b"hello\0"); assert!(cstr.is_ok());
Creating a CStr
without a trailing nul terminator is an error:
use drone_core::ffi::CStr; let c_str = CStr::from_bytes_with_nul(b"hello"); assert!(c_str.is_err());
Creating a CStr
with an interior nul byte is an error:
use drone_core::ffi::CStr; let c_str = CStr::from_bytes_with_nul(b"he\0llo\0"); assert!(c_str.is_err());
pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &Self
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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 drone_core::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); }
pub const fn as_ptr(&self) -> *const c_char
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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 drone_core::ffi::CString; let ptr = CString::new("Hello").expect("CString::new failed").as_ptr(); unsafe { // `ptr` is dangling *ptr; }
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 drone_core::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; }
This way, the lifetime of the CString
in hello
encompasses the
lifetime of ptr
and the unsafe
block.
pub fn to_bytes(&self) -> &[u8]
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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 drone_core::ffi::CStr; let c_str = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"); assert_eq!(c_str.to_bytes(), b"foo");
pub fn to_bytes_with_nul(&self) -> &[u8]
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Converts this C string to a byte slice containing the trailing 0 byte.
This function is the equivalent of CStr::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 drone_core::ffi::CStr; let c_str = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"); assert_eq!(c_str.to_bytes_with_nul(), b"foo\0");
pub fn to_str(&self) -> Result<&str, Utf8Error>
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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 drone_core::ffi::CStr; let c_str = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"); assert_eq!(c_str.to_str(), Ok("foo"));
pub fn to_string_lossy(&self) -> Cow<'_, str>
[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 alloc::borrow::Cow; use drone_core::ffi::CStr; let c_str = CStr::from_bytes_with_nul(b"Hello World\0").expect("CStr::from_bytes_with_nul failed"); assert_eq!(c_str.to_string_lossy(), Cow::Borrowed("Hello World"));
Calling to_string_lossy
on a CStr
containing invalid UTF-8:
use alloc::borrow::Cow; use drone_core::ffi::CStr; let c_str = CStr::from_bytes_with_nul(b"Hello \xF0\x90\x80World\0") .expect("CStr::from_bytes_with_nul failed"); assert_eq!(c_str.to_string_lossy(), Cow::Owned(String::from("Hello �World")) as Cow<'_, str>);
pub fn into_c_string(self: Box<Self>) -> CString
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Converts a Box
<CStr>
into a CString
without copying or
allocating.
Examples
use drone_core::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"));
Trait Implementations
impl AsRef<CStr> for CStr
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impl AsRef<CStr> for CString
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impl Borrow<CStr> for CString
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impl Debug for CStr
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impl Default for &CStr
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impl Eq for CStr
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impl From<&'_ CStr> for CString
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impl Hash for CStr
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fn hash<__H: Hasher>(&self, state: &mut __H)
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pub fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,
1.3.0[src]
H: Hasher,