Struct std::ffi::CString 1.0.0
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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
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 .unwrap() let c_to_print = CString::new("Hello, world!").unwrap(); 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!").unwrap(); 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) -> CString1.4.0[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
Create 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!").unwrap(); 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_char1.4.0[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").unwrap(); 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).unwrap(); assert_eq!(cstring.into_string().unwrap(), "foo"); let invalid_utf8 = vec![b'f', 0xff, b'o', b'o']; let cstring = CString::new(invalid_utf8).unwrap(); let err = cstring.into_string().err().unwrap(); 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").unwrap(); 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").unwrap(); 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").unwrap(); 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").unwrap(); 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) -> &CStr1.20.0[src]
Extracts a CStr slice containing the entire string.
Examples
use std::ffi::{CString, CStr}; let c_string = CString::new(b"foo".to_vec()).unwrap(); let c_str = c_string.as_c_str(); assert_eq!(c_str, CStr::from_bytes_with_nul(b"foo\0").unwrap());Run
pub fn into_boxed_c_str(self) -> Box<CStr>1.20.0[src]
Methods from Deref<Target = CStr>
pub 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").unwrap().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").unwrap().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").unwrap(); 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 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").unwrap(); 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").unwrap(); 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 0-cost 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").unwrap(); 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 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 0-cost 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").unwrap(); 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").unwrap(); assert_eq!( c_str.to_string_lossy(), Cow::Owned(String::from("Hello �World")) as Cow<str> );Run
Trait Implementations
impl PartialEq for CString[src]
fn eq(&self, __arg_0: &CString) -> bool[src]
This method tests for self and other values to be equal, and is used by ==. Read more
fn ne(&self, __arg_0: &CString) -> bool[src]
This method tests for !=.
impl PartialOrd for CString[src]
fn partial_cmp(&self, __arg_0: &CString) -> Option<Ordering>[src]
This method returns an ordering between self and other values if one exists. Read more
fn lt(&self, __arg_0: &CString) -> bool[src]
This method tests less than (for self and other) and is used by the < operator. Read more
fn le(&self, __arg_0: &CString) -> bool[src]
This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
fn gt(&self, __arg_0: &CString) -> bool[src]
This method tests greater than (for self and other) and is used by the > operator. Read more
fn ge(&self, __arg_0: &CString) -> bool[src]
This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more
impl Eq for CString[src]
impl Ord for CString[src]
fn cmp(&self, __arg_0: &CString) -> Ordering[src]
This method returns an Ordering between self and other. Read more
fn max(self, other: Self) -> Self1.21.0[src]
Compares and returns the maximum of two values. Read more
fn min(self, other: Self) -> Self1.21.0[src]
Compares and returns the minimum of two values. Read more
impl Hash for CString[src]
fn hash<__H: Hasher>(&self, __arg_0: &mut __H)[src]
Feeds this value into the given [Hasher]. Read more
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 Clone for CString[src]
fn clone(&self) -> CString[src]
Returns a copy of the value. Read more
fn clone_from(&mut self, source: &Self)[src]
Performs copy-assignment from source. Read more
impl Drop for CString1.13.0[src]
impl Deref for CString[src]
type Target = CStr
The resulting type after dereferencing.
fn deref(&self) -> &CStr[src]
Dereferences the value.
impl Debug for CString[src]
fn fmt(&self, f: &mut Formatter) -> Result[src]
Formats the value using the given formatter. Read more
impl From<CString> for Vec<u8>1.7.0[src]
impl Default for CString1.10.0[src]
impl Borrow<CStr> for CString1.3.0[src]
impl From<Box<CStr>> for CString1.18.0[src]
impl From<CString> for Box<CStr>1.20.0[src]
impl<'a> From<&'a CStr> for CString1.7.0[src]
impl Index<RangeFull> for CString1.7.0[src]
type Output = CStr
The returned type after indexing.
fn index(&self, _index: RangeFull) -> &CStr[src]
Performs the indexing (container[index]) operation.