Struct drone_core::ffi::CString [−][src]
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 &
CStr
as String
is to &
str
: 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 Into
<
Vec
<
u8
>>
(for example, you
can build a CString
straight out of a String
or a &
str
, since
both implement that trait).
The CString::new
method will actually check that the provided &[u8]
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 a as_ptr
method through the core::ops::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
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 &[
u8
]
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
method.
If you need a &[
u8
]
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
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.
Examples
use drone_core::ffi::{c_char, CString}; 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.
Implementations
impl CString
[src]
pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<Self, NulError>
[src]
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
use drone_core::ffi::{c_char, CString}; 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.
pub unsafe fn from_vec_unchecked(v: Vec<u8>) -> Self
[src]
Creates a C-compatible string by consuming a byte vector, without checking for interior 0 bytes.
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 drone_core::ffi::CString; let raw = b"foo".to_vec(); unsafe { let c_string = CString::from_vec_unchecked(raw); }
pub unsafe fn from_raw(ptr: *mut c_char) -> Self
[src]
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
on a CString
. 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.
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
:
use drone_core::ffi::{c_char, CString}; 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); }
pub fn into_raw(self) -> *mut c_char
[src]
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.
Examples
use drone_core::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.offset(1) as u8); assert_eq!(b'o', *ptr.offset(2) as u8); assert_eq!(b'\0', *ptr.offset(3) as u8); // retake pointer to free memory let _ = CString::from_raw(ptr); }
pub fn into_string(self) -> Result<String, IntoStringError>
[src]
Converts the CString
into a String
if it contains valid UTF-8
data.
On failure, ownership of the original CString
is returned.
Examples
use drone_core::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);
pub fn into_bytes(self) -> Vec<u8>
[src]
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 drone_core::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']);
pub fn into_bytes_with_nul(self) -> Vec<u8>
[src]
Equivalent to the CString::into_bytes
function except that the
returned vector includes the trailing nul terminator.
Examples
use drone_core::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']);
pub fn as_bytes(&self) -> &[u8]
[src]
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 drone_core::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']);
pub fn as_bytes_with_nul(&self) -> &[u8]
[src]
Equivalent to the CString::as_bytes
function except that the
returned slice includes the trailing nul terminator.
Examples
use drone_core::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']);
pub fn as_c_str(&self) -> &CStr
[src]
Extracts a CStr
slice containing the entire string.
Examples
use drone_core::ffi::{CStr, CString}; let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed"); let c_str = c_string.as_c_str(); assert_eq!( c_str, CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed") );
pub fn into_boxed_c_str(self) -> Box<CStr>
[src]
Converts this CString
into a boxed CStr
.
Examples
use drone_core::ffi::{CStr, 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, CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed") );
Methods from Deref<Target = CStr>
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 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]
[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 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]
[src]
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>
[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 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>);
Trait Implementations
impl AsRef<CStr> for CString
[src]
impl Borrow<CStr> for CString
[src]
impl Clone for CString
[src]
fn clone(&self) -> CString
[src]
pub fn clone_from(&mut self, source: &Self)
1.0.0[src]
impl Debug for CString
[src]
impl Default for CString
[src]
impl Deref for CString
[src]
impl Drop for CString
[src]
impl Eq for CString
[src]
impl From<&'_ CStr> for CString
[src]
impl From<Box<CStr, Global>> for CString
[src]
impl<'a> From<Cow<'a, CStr>> for CString
[src]
impl Hash for CString
[src]
fn hash<__H: Hasher>(&self, state: &mut __H)
[src]
pub fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,
1.3.0[src]
H: Hasher,
impl Index<RangeFull> for CString
[src]
type Output = CStr
The returned type after indexing.
fn index(&self, _index: RangeFull) -> &CStr
[src]
impl Ord for CString
[src]
fn cmp(&self, other: &CString) -> Ordering
[src]
#[must_use]pub fn max(self, other: Self) -> Self
1.21.0[src]
#[must_use]pub fn min(self, other: Self) -> Self
1.21.0[src]
#[must_use]pub fn clamp(self, min: Self, max: Self) -> Self
1.50.0[src]
impl PartialEq<CString> for CString
[src]
impl PartialOrd<CString> for CString
[src]
fn partial_cmp(&self, other: &CString) -> Option<Ordering>
[src]
#[must_use]pub fn lt(&self, other: &Rhs) -> bool
1.0.0[src]
#[must_use]pub fn le(&self, other: &Rhs) -> bool
1.0.0[src]
#[must_use]pub fn gt(&self, other: &Rhs) -> bool
1.0.0[src]
#[must_use]pub fn ge(&self, other: &Rhs) -> bool
1.0.0[src]
impl StructuralEq for CString
[src]
impl StructuralPartialEq for CString
[src]
Auto Trait Implementations
Blanket Implementations
impl<T> Any for T where
T: 'static + ?Sized,
[src]
T: 'static + ?Sized,
impl<T> Borrow<T> for T where
T: ?Sized,
[src]
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
pub fn borrow_mut(&mut self) -> &mut T
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impl<T> From<T> for T
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T> Same<T> for T
[src]
type Output = T
Should always be Self
impl<T> ToOwned for T where
T: Clone,
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T: Clone,
type Owned = T
The resulting type after obtaining ownership.
pub fn to_owned(&self) -> T
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pub fn clone_into(&self, target: &mut T)
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impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,