1.0.0[−][src]Struct std::ffi::CString
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 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 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 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 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 std::ffi::CString; use std::os::raw::c_char; extern { 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()); }Run
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.
Methods
impl CString
[src]
pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<CString, 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 std::ffi::CString; use std::os::raw::c_char; extern { fn puts(s: *const c_char); } let to_print = CString::new("Hello!").expect("CString::new failed"); unsafe { puts(to_print.as_ptr()); }Run
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>) -> CString
[src]
Creates a C-compatible string by consuming a byte vector, without checking for interior 0 bytes.
This method is equivalent to 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); }Run
pub unsafe fn from_raw(ptr: *mut c_char) -> CString
1.4.0[src]
Retakes ownership of a CString
that was transferred to C via 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 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 std::ffi::CString; use std::os::raw::c_char; extern { 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); }Run
pub fn into_raw(self) -> *mut c_char
1.4.0[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
from_raw
to be properly deallocated. Specifically, one
should not use the standard C free()
function to deallocate
this string.
Failure to call from_raw
will lead to a memory leak.
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.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); }Run
pub fn into_string(self) -> Result<String, IntoStringError>
1.7.0[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 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);Run
pub fn into_bytes(self) -> Vec<u8>
1.7.0[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 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']);Run
pub fn into_bytes_with_nul(self) -> Vec<u8>
1.7.0[src]
Equivalent to the into_bytes
function 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']);Run
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
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']);Run
pub fn as_bytes_with_nul(&self) -> &[u8]
[src]
Equivalent to the as_bytes
function 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']);Run
pub fn as_c_str(&self) -> &CStr
1.20.0[src]
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 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"));Run
ⓘImportant traits for Box<I>pub fn into_boxed_c_str(self) -> Box<CStr>
1.20.0[src]
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"));Run
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 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 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");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 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");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 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"));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 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"));Run
Calling to_string_lossy
on a CStr
containing invalid UTF-8:
use std::borrow::Cow; use std::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> );Run
Trait Implementations
impl Deref for CString
[src]
impl PartialEq<CString> for CString
[src]
impl Eq for CString
[src]
impl Ord for CString
[src]
fn cmp(&self, other: &CString) -> Ordering
[src]
fn max(self, other: Self) -> Self
1.21.0[src]
Compares and returns the maximum of two values. Read more
fn min(self, other: Self) -> Self
1.21.0[src]
Compares and returns the minimum of two values. Read more
fn clamp(self, min: Self, max: Self) -> Self
[src]
Restrict a value to a certain interval. Read more
impl PartialOrd<CString> for CString
[src]
fn partial_cmp(&self, other: &CString) -> Option<Ordering>
[src]
fn lt(&self, other: &CString) -> bool
[src]
fn le(&self, other: &CString) -> bool
[src]
fn gt(&self, other: &CString) -> bool
[src]
fn ge(&self, other: &CString) -> bool
[src]
impl Hash for CString
[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,
Feeds a slice of this type into the given [Hasher
]. Read more
impl Debug for CString
[src]
impl Drop for CString
1.13.0[src]
impl Index<RangeFull> for CString
1.7.0[src]
type Output = CStr
The returned type after indexing.
fn index(&self, _index: RangeFull) -> &CStr
[src]
impl AsRef<CStr> for CString
1.7.0[src]
impl From<CString> for Vec<u8>
1.7.0[src]
impl<'a> From<Cow<'a, CStr>> for CString
1.28.0[src]
impl From<Box<CStr>> for CString
1.18.0[src]
impl From<CString> for Box<CStr>
1.20.0[src]
impl<'a> From<CString> for Cow<'a, CStr>
1.28.0[src]
impl<'a> From<&'a CString> for Cow<'a, CStr>
1.28.0[src]
impl From<CString> for Arc<CStr>
1.24.0[src]
impl From<CString> for Rc<CStr>
1.24.0[src]
impl<'_> From<&'_ CStr> for CString
1.7.0[src]
impl Clone for CString
[src]
fn clone(&self) -> CString
[src]
fn clone_from(&mut self, source: &Self)
[src]
Performs copy-assignment from source
. Read more
impl Default for CString
1.10.0[src]
impl Borrow<CStr> for CString
1.3.0[src]
Auto Trait Implementations
Blanket Implementations
impl<T, U> TryFrom<U> for T where
U: Into<T>,
[src]
U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
[src]
impl<T, U> Into<U> for T where
U: From<T>,
[src]
U: From<T>,
impl<T> From<T> for T
[src]
impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
[src]
U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
[src]
impl<T> Borrow<T> for T where
T: ?Sized,
[src]
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
[src]
T: ?Sized,
ⓘImportant traits for &'_ mut Ffn borrow_mut(&mut self) -> &mut T
[src]
impl<T> Any for T where
T: 'static + ?Sized,
[src]
T: 'static + ?Sized,
impl<T> ToOwned for T where
T: Clone,
[src]
T: Clone,