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

pub struct CStr { /* fields omitted */ }

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 from_ptr constructor to provide a safe interface to other consumers.

Examples

Inspecting a foreign C string:

This example is not tested
use std::ffi::CStr;
use std::os::raw::c_char;

extern { 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());
}Run

Passing a Rust-originating C string:

This example is not tested
use std::ffi::{CString, CStr};
use std::os::raw::c_char;

fn work(data: &CStr) {
    extern { 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);Run

Converting a foreign C string into a Rust String:

This example is not tested
use std::ffi::CStr;
use std::os::raw::c_char;

extern { 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());Run

Methods

impl CStr
[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 the CStr 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

This example is not tested
use std::ffi::CStr;
use std::os::raw::c_char;

extern {
    fn my_string() -> *const c_char;
}

unsafe {
    let slice = CStr::from_ptr(my_string());
    println!("string returned: {}", slice.to_str().unwrap());
}Run

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());Run

Creating a CStr without a trailing nul terminator is an error:

use std::ffi::CStr;

let c_str = CStr::from_bytes_with_nul(b"hello");
assert!(c_str.is_err());Run

Creating a CStr with an interior nul byte is an error:

use std::ffi::CStr;

let c_str = CStr::from_bytes_with_nul(b"he\0llo\0");
assert!(c_str.is_err());Run

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);
}Run

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 &'a [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 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 &'a [u8]

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

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

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 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

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"));Run

Trait Implementations

impl Hash for CStr
[src]

Feeds this value into the given [Hasher]. Read more

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

impl Debug for CStr
1.3.0
[src]

Formats the value using the given formatter. Read more

impl<'a> Default for &'a CStr
1.10.0
[src]

Returns the "default value" for a type. Read more

impl Borrow<CStr> for CString
1.3.0
[src]

Immutably borrows from an owned value. Read more

impl<'a> From<&'a CStr> for Box<CStr>
1.17.0
[src]

Important traits for Box<I>

Performs the conversion.

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

Performs the conversion.

impl<'a> From<&'a CStr> for Arc<CStr>
1.24.0
[src]

Performs the conversion.

impl<'a> From<&'a CStr> for Rc<CStr>
1.24.0
[src]

Performs the conversion.

impl PartialEq for CStr
[src]

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

impl Eq for CStr
[src]

impl PartialOrd for CStr
[src]

This method returns an ordering between self and other values if one exists. Read more

This method tests less than (for self and other) and is used by the < operator. Read more

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

This method tests greater than (for self and other) and is used by the > operator. Read more

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

impl Ord for CStr
[src]

This method returns an Ordering between self and other. Read more

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

impl ToOwned for CStr
1.3.0
[src]

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (toowned_clone_into #41263)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

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

Performs the conversion.

impl AsRef<CStr> for CStr
1.7.0
[src]

Performs the conversion.

impl AsRef<CStr> for CString
1.7.0
[src]

Performs the conversion.

Auto Trait Implementations

impl Send for CStr

impl Sync for CStr

Blanket Implementations

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

Important traits for &'a mut I

Immutably borrows from an owned value. Read more

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

Important traits for &'a mut I

Mutably borrows from an owned value. Read more

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

🔬 This is a nightly-only experimental API. (get_type_id #27745)

this method will likely be replaced by an associated static

Gets the TypeId of self. Read more

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

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (toowned_clone_into #41263)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more