Struct jni::strings::JavaStr

pub struct JavaStr<'local, 'other_local: 'obj_ref, 'obj_ref> { /* private fields */ }

Reference to a string in the JVM. Holds a pointer to the array returned by GetStringUTFChars. Calls ReleaseStringUTFChars on Drop. Can be converted to a &JNIStr with the same cost as the &CStr.from_ptr conversion.

Implementations

impl<'local, 'other_local: 'obj_ref, 'obj_ref> JavaStr<'local, 'other_local, 'obj_ref>

pub fn from_env( env: &JNIEnv<'local>, obj: &'obj_ref JString<'other_local> ) -> Result<Self>

Get a JavaStr from a JNIEnv and a JString. You probably want JNIEnv::get_string instead of this method.

pub fn get_raw(&self) -> *const c_char

Get the raw string pointer from the JavaStr.

The string will be NULL terminated and encoded as Modified UTF-8 / CESU-8.

pub fn into_raw(self) -> *const c_char

Consumes the JavaStr, returning the raw string pointer

The string will be NULL terminated and encoded as Modified UTF-8 / CESU-8.

Warning

The programmer is responsible for making sure the backing string gets released when they are done with it, for example by reconstructing a JavaStr with Self::from_raw, which will release the backing string when it is dropped.

pub unsafe fn from_raw( env: &JNIEnv<'local>, obj: &'obj_ref JString<'other_local>, ptr: *const c_char ) -> Self

Get a JavaStr from it’s raw components

Safety

The caller must guarantee that ptr is a valid, non-null pointer returned by Self::into_raw, and that obj is the same String object originally used to create the JavaStr

Example

let jstring = env.new_string("foo")?;
let java_str = env.get_string(&jstring)?;

let ptr = java_str.into_raw();
// Do whatever you need with the pointer
let java_str = unsafe { JavaStr::from_raw(env, &jstring, ptr) };

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::CString;

// Do not do this:
let ptr = CString::new("Hello").expect("CString::new failed").as_ptr();
unsafe {
    // `ptr` is dangling
    *ptr;
}

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;
}

This way, the lifetime of the CString in hello encompasses the lifetime of ptr and the unsafe block.

pub fn is_empty(&self) -> bool

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

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

Examples

#![feature(cstr_is_empty)]

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());

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 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:

use std::borrow::Cow;
use std::ffi::CStr;

let cstr = CStr::from_bytes_with_nul(b"Hello World\0")
                 .expect("CStr::from_bytes_with_nul failed");
assert_eq!(cstr.to_string_lossy(), Cow::Borrowed("Hello World"));

Calling to_string_lossy on a CStr containing invalid UTF-8:

use std::borrow::Cow;
use std::ffi::CStr;

let cstr = CStr::from_bytes_with_nul(b"Hello \xF0\x90\x80World\0")
                 .expect("CStr::from_bytes_with_nul failed");
assert_eq!(
    cstr.to_string_lossy(),
    Cow::Owned(String::from("Hello �World")) as Cow<'_, str>
);

Trait Implementations

impl<'local, 'other_local: 'obj_ref, 'obj_ref> Deref for JavaStr<'local, 'other_local, 'obj_ref>

type Target = JNIStr

The resulting type after dereferencing.

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

Dereferences the value.

impl<'local, 'other_local: 'obj_ref, 'obj_ref> Drop for JavaStr<'local, 'other_local, 'obj_ref>

fn drop(&mut self)

Executes the destructor for this type.

impl<'local, 'other_local: 'obj_ref, 'obj_ref: 'java_str, 'java_str> From<&'java_str JavaStr<'local, 'other_local, 'obj_ref>> for &'java_str JNIStr

fn from(other: &'java_str JavaStr<'_, '_, '_>) -> &'java_str JNIStr

Converts to this type from the input type.

impl<'local, 'other_local: 'obj_ref, 'obj_ref: 'java_str, 'java_str> From<&'java_str JavaStr<'local, 'other_local, 'obj_ref>> for Cow<'java_str, str>

fn from(other: &'java_str JavaStr<'_, '_, '_>) -> Cow<'java_str, str>

Converts to this type from the input type.

impl<'local, 'other_local: 'obj_ref, 'obj_ref> From<JavaStr<'local, 'other_local, 'obj_ref>> for String

fn from(other: JavaStr<'_, '_, '_>) -> String

Converts to this type from the input type.