Struct std::ffi::CStr
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[src]
pub struct CStr {
// some fields omitted
}Representation of a borrowed C string.
This dynamically sized type is only safely constructed via a borrowed
version of an instance of CString. This type can be constructed from a raw
C string as well and represents a C string borrowed from another location.
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
use std::ffi::CStr; use std::os::raw::c_char; extern { fn my_string() -> *const c_char; } fn main() { unsafe { let slice = CStr::from_ptr(my_string()); println!("string length: {}", slice.to_bytes().len()); } }use std::ffi::CStr; use std::os::raw::c_char; extern { fn my_string() -> *const c_char; } fn main() { unsafe { let slice = CStr::from_ptr(my_string()); println!("string length: {}", 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 { fn work_with(data: *const c_char); } unsafe { work_with(data.as_ptr()) } } fn main() { let s = CString::new("data data data data").unwrap(); work(&s); }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()) } } fn main() { let s = CString::new("data data data data").unwrap(); work(&s); }
Converting a foreign C string into a Rust String
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() } } fn main() { println!("string: {}", my_string_safe()); }
Methods
impl CStr
unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr
Casts a raw C string to a safe C string wrapper.
This function will cast the provided ptr to the 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
ptrcontains a valid nul terminator byte at the end of the string.
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
fn main() { use std::ffi::CStr; use std::os::raw::c_char; use std::str; extern { fn my_string() -> *const c_char; } unsafe { let slice = CStr::from_ptr(my_string()); println!("string returned: {}", str::from_utf8(slice.to_bytes()).unwrap()); } }use std::ffi::CStr; use std::os::raw::c_char; use std::str; extern { fn my_string() -> *const c_char; } unsafe { let slice = CStr::from_ptr(my_string()); println!("string returned: {}", str::from_utf8(slice.to_bytes()).unwrap()); }
fn as_ptr(&self) -> *const c_char
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.
fn to_bytes(&self) -> &[u8]
Converts this C string to a byte slice.
This function will calculate the length of this string (which normally
requires a linear amount of work to be done) and then return the
resulting slice of u8 elements.
The returned slice will not contain the trailing nul 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.
fn to_bytes_with_nul(&self) -> &[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 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.
fn to_str(&self) -> Result<&str, Utf8Error>
Yields a &str slice if the CStr contains valid UTF-8.
This function will calculate the length of this string and check for
UTF-8 validity, and then return the &str if it's valid.
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.
fn to_string_lossy(&self) -> Cow<str>
Converts a CStr into a Cow<str>.
This function will calculate the length of this string (which normally
requires a linear amount of work to be done) and then return the
resulting slice as a Cow<str>, replacing any invalid UTF-8 sequences
with U+FFFD REPLACEMENT CHARACTER.
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.