1.0.0[][src]Struct std::ffi::CString

pub struct CString { /* fields omitted */ }

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().

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 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

This example is not tested
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

This example is not tested
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:

This example is not tested
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

Important traits for Vec<u8>
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

Important traits for Vec<u8>
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

Important traits for &'_ [u8]
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

Important traits for &'_ [u8]
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

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.

Important traits for &'_ [u8]
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

Important traits for &'_ [u8]
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 Debug for CString[src]

impl PartialEq<CString> for CString[src]

impl Eq for CString[src]

impl Ord for CString[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]

🔬 This is a nightly-only experimental API. (clamp #44095)

Restrict a value to a certain interval. Read more

impl PartialOrd<CString> for CString[src]

impl From<CString> for Vec<u8>
1.7.0
[src]

Important traits for Vec<u8>
fn from(s: CString) -> Vec<u8>[src]

Converts a CString into a Vec<u8>.

The conversion consumes the CString, and removes the terminating NUL byte.

impl<'a> From<Cow<'a, CStr>> for CString
1.28.0
[src]

impl From<Box<CStr>> for CString
1.18.0
[src]

fn from(s: Box<CStr>) -> CString[src]

Converts a Box<CStr> into a CString without copying or allocating.

impl From<CString> for Box<CStr>
1.20.0
[src]

Important traits for Box<I>
fn from(s: CString) -> Box<CStr>[src]

Converts a CString into a Box<CStr> without copying or allocating.

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]

fn from(s: CString) -> Arc<CStr>[src]

Converts a CString into a Arc<CStr> without copying or allocating.

impl From<CString> for Rc<CStr>
1.24.0
[src]

fn from(s: CString) -> Rc<CStr>[src]

Converts a CString into a Rc<CStr> without copying or allocating.

impl<'_> From<&'_ CStr> for CString
1.7.0
[src]

impl Hash for CString[src]

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher
1.3.0
[src]

Feeds a slice of this type into the given [Hasher]. Read more

impl Deref for CString[src]

type Target = CStr

The resulting type after dereferencing.

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.

impl Clone for 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]

fn default() -> CString[src]

Creates an empty CString.

impl AsRef<CStr> for CString
1.7.0
[src]

impl Borrow<CStr> for CString
1.3.0
[src]

Auto Trait Implementations

impl Send for CString

impl Sync for CString

Blanket Implementations

impl<T> From for T[src]

impl<T, U> TryFrom for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<T, U> Into for T where
    U: From<T>, 
[src]

impl<T> Borrow for T where
    T: ?Sized
[src]

impl<T> BorrowMut for T where
    T: ?Sized
[src]

impl<T> Any for T where
    T: 'static + ?Sized
[src]

impl<T> ToOwned for T where
    T: Clone
[src]

type Owned = T