pub struct CStr { /* private fields */ }
Expand description
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 std::ffi::CStr;
use std::os::raw::c_char;
extern "C" { 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());
}
Passing a Rust-originating C string:
use std::ffi::{CString, CStr};
use std::os::raw::c_char;
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 std::ffi::CStr;
use std::os::raw::c_char;
extern "C" { 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());
Implementations
sourceimpl CStr
impl CStr
sourcepub unsafe fn from_ptr<'a>(ptr: *const i8) -> &'a CStr
pub unsafe fn from_ptr<'a>(ptr: *const i8) -> &'a CStr
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 "C" {
fn my_string() -> *const c_char;
}
unsafe {
let slice = CStr::from_ptr(my_string());
println!("string returned: {}", slice.to_str().unwrap());
}
1.10.0 · sourcepub fn from_bytes_with_nul(bytes: &[u8]) -> Result<&CStr, FromBytesWithNulError>
pub fn from_bytes_with_nul(bytes: &[u8]) -> Result<&CStr, FromBytesWithNulError>
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());
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());
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());
1.10.0 (const: 1.59.0) · sourcepub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr
pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr
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);
}
const: 1.32.0 · sourcepub const fn as_ptr(&self) -> *const i8
pub const fn as_ptr(&self) -> *const i8
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;
}
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;
}
This way, the lifetime of the CString
in hello
encompasses
the lifetime of ptr
and the unsafe
block.
sourcepub fn to_bytes(&self) -> &[u8]ⓘNotable traits for &'_ [u8]impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]
pub fn to_bytes(&self) -> &[u8]ⓘNotable traits for &'_ [u8]impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]
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");
sourcepub fn to_bytes_with_nul(&self) -> &[u8]ⓘNotable traits for &'_ [u8]impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]
pub fn to_bytes_with_nul(&self) -> &[u8]ⓘNotable traits for &'_ [u8]impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]
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 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");
1.4.0 · sourcepub fn to_str(&self) -> Result<&str, Utf8Error>
pub fn to_str(&self) -> Result<&str, Utf8Error>
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.
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"));
1.4.0 · sourcepub fn to_string_lossy(&self) -> Cow<'_, str>
pub fn to_string_lossy(&self) -> Cow<'_, str>
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(&str)
with the result.
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>
);
1.20.0 · sourcepub fn into_c_string(self: Box<CStr, Global>) -> CString
pub fn into_c_string(self: Box<CStr, Global>) -> CString
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"));
Trait Implementations
sourceimpl Arg for &CStr
impl Arg for &CStr
sourcefn to_string_lossy(&self) -> Cow<'_, str>
fn to_string_lossy(&self) -> Cow<'_, str>
Returns a potentially-lossy rendering of this string as a Cow<'_, str>
. Read more
sourcefn as_cow_c_str(&self) -> Result<Cow<'_, CStr>>
fn as_cow_c_str(&self) -> Result<Cow<'_, CStr>>
Returns a view of this string as a maybe-owned CStr
.
sourcefn into_c_str<'b>(self) -> Result<Cow<'b, CStr>> where
Self: 'b,
fn into_c_str<'b>(self) -> Result<Cow<'b, CStr>> where
Self: 'b,
sourceimpl Ord for CStr
impl Ord for CStr
sourceimpl PartialOrd<CStr> for CStr
impl PartialOrd<CStr> for CStr
sourcefn partial_cmp(&self, other: &CStr) -> Option<Ordering>
fn partial_cmp(&self, other: &CStr) -> Option<Ordering>
This method returns an ordering between self
and other
values if one exists. Read more
sourcefn lt(&self, other: &Rhs) -> bool
fn lt(&self, other: &Rhs) -> bool
This method tests less than (for self
and other
) and is used by the <
operator. Read more
sourcefn le(&self, other: &Rhs) -> bool
fn le(&self, other: &Rhs) -> bool
This method tests less than or equal to (for self
and other
) and is used by the <=
operator. Read more