Struct LLVMString

pub struct LLVMString { /* private fields */ }

An owned LLVM String. Also known as a LLVM Message

Implementations

impl LLVMString

pub fn to_string(&self) -> String

This is a convenience method for creating a Rust String, however; it will reallocate. LLVMString should be used as much as possible to save memory since it is allocated by LLVM. It’s essentially a CString with a custom LLVM deallocator

Methods from Deref<Target = CStr>

pub 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.

The type of the returned pointer is *const c_char, and whether it’s an alias for *const i8 or *const u8 is platform-specific.

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::{CStr, CString};

// 💀 The meaning of this entire program is undefined,
// 💀 and nothing about its behavior is guaranteed,
// 💀 not even that its behavior resembles the code as written,
// 💀 just because it contains a single instance of undefined behavior!

// 🚨 creates a dangling pointer to a temporary `CString`
// 🚨 that is deallocated at the end of the statement
let ptr = CString::new("Hi!".to_uppercase()).unwrap().as_ptr();

// without undefined behavior, you would expect that `ptr` equals:
dbg!(CStr::from_bytes_with_nul(b"HI!\0").unwrap());

// 🙏 Possibly the program behaved as expected so far,
// 🙏 and this just shows `ptr` is now garbage..., but
// 💀 this violates `CStr::from_ptr`'s safety contract
// 💀 leading to a dereference of a dangling pointer,
// 💀 which is immediate undefined behavior.
// 💀 *BOOM*, you're dead, you're entire program has no meaning.
dbg!(unsafe { CStr::from_ptr(ptr) });

This happens because, the pointer returned by as_ptr does not carry any lifetime information, and the CString is deallocated immediately after the expression that it is part of has been evaluated. To fix the problem, bind the CString to a local variable:

use std::ffi::{CStr, CString};

let c_str = CString::new("Hi!".to_uppercase()).unwrap();
let ptr = c_str.as_ptr();

assert_eq!(unsafe { CStr::from_ptr(ptr) }, c"HI!");

pub fn count_bytes(&self) -> usize

Returns the length of self. Like C’s strlen, this does not include the nul terminator.

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").unwrap();
assert_eq!(cstr.count_bytes(), 3);

let cstr = CStr::from_bytes_with_nul(b"\0").unwrap();
assert_eq!(cstr.count_bytes(), 0);

pub fn is_empty(&self) -> bool

Returns true if self.to_bytes() has a length of 0.

Examples

use std::ffi::CStr;

let cstr = CStr::from_bytes_with_nul(b"foo\0")?;
assert!(!cstr.is_empty());

let empty_cstr = CStr::from_bytes_with_nul(b"\0")?;
assert!(empty_cstr.is_empty());
assert!(c"".is_empty());

pub fn to_bytes(&self) -> &[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");

pub 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 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");

pub fn bytes(&self) -> Bytes<'_>

🔬This is a nightly-only experimental API. (cstr_bytes)

Iterates over the bytes in this C string.

The returned iterator will not contain the trailing nul terminator that this C string has.

Examples

#![feature(cstr_bytes)]
use std::ffi::CStr;

let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
assert!(cstr.bytes().eq(*b"foo"));

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"));

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. The leading c on the string literal denotes a CStr.

use std::borrow::Cow;

assert_eq!(c"Hello World".to_string_lossy(), Cow::Borrowed("Hello World"));

Calling to_string_lossy on a CStr containing invalid UTF-8:

use std::borrow::Cow;

assert_eq!(
    c"Hello \xF0\x90\x80World".to_string_lossy(),
    Cow::Owned(String::from("Hello �World")) as Cow<'_, str>
);

Trait Implementations

impl Debug for LLVMString

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Deref for LLVMString

type Target = CStr

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl Display for LLVMString

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Drop for LLVMString

fn drop(&mut self)

Executes the destructor for this type.

impl Error for LLVMString

fn description(&self) -> &str

👎Deprecated since 1.42.0: use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl PartialEq for LLVMString

fn eq(&self, other: &LLVMString) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Eq for LLVMString