Crate widestring

A wide string FFI library for converting to and from Windows Wide "Unicode" strings.

This crate provides two types of wide strings: WideString and WideCString. They differ in the guaruntees they provide. For WideString, no guaruntees are made about the underlying string data; it is simply a sequence of UTF-16 values, which may be ill-formed or contain nul values. WideCString on the other hand is aware of nul values and is guarunteed to be terminated with a nul value (unless unchecked methods are used to construct the WideCString). Because WideCString is a C-style, nul-terminated string, it will have no interior nul values. A WideCString may still have ill-formed UTF-16 values.

Use WideString when you simply need to pass-thru values, or when you know or don't care if you're not dealing with a nul-terminated string, such as when string lengths are provided and you are only reading strings from FFI, not passing them into FFI.

Use WideCString when you must properly handle nul values, and must deal with nul-terminated C-style wide strings, such as if you must pass string values into FFI functions.

While these types are roughly based on the types in std::os, they are not an identical wide version of OsString and CString, but do fill a similar, adjacent role.

Examples

The following example uses WideString to get windows error messages, since FormatMessageW returns a string length for us, and we don't need to pass error messages into other FFI functions so we don't need to worry about nuls.

use winapi::*;
use kernel32::{FormatMessageW, LocalFree};
use std::ptr;
use widestring::WideString;

let widestr: WideString;
unsafe {
    // First, get a string buffer from some windows api such as FormatMessageW...
    let mut buffer: LPWSTR = ptr::null_mut();
    let strlen = FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM |
                                FORMAT_MESSAGE_ALLOCATE_BUFFER |
                                FORMAT_MESSAGE_IGNORE_INSERTS,
                                ptr::null(),
                                error_code, // error code from GetLastError()
                                0,
                                (&mut buffer as *mut LPWSTR) as LPWSTR,
                                0,
                                ptr::null_mut());

    // Get the buffer as a wide string
    widestr = WideString::from_ptr(buffer, strlen as usize);
    // Since WideString creates an owned copy, it's safe to free original buffer now
    // If you didn't want an owned copy, you could use &WideStr.
    LocalFree(buffer as HLOCAL);
}
// Convert to a regular Rust String and use it to your heart's desire!
let message = widestr.to_string_lossy();

The following example is the functionally the same, only using WideCString instead.

use winapi::*;
use kernel32::{FormatMessageW, LocalFree};
use std::ptr;
use widestring::WideCString;

let widestr: WideCString;
unsafe {
    // First, get a string buffer from some windows api such as FormatMessageW...
    let mut buffer: LPWSTR = ptr::null_mut();
    FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM |
                   FORMAT_MESSAGE_ALLOCATE_BUFFER |
                   FORMAT_MESSAGE_IGNORE_INSERTS,
                   ptr::null(),
                   error_code, // error code from GetLastError()
                   0,
                   (&mut buffer as *mut LPWSTR) as LPWSTR,
                   0,
                   ptr::null_mut());

    // Get the buffer as a wide string
    widestr = WideCString::from_ptr_str(buffer);
    // Since WideCString creates an owned copy, it's safe to free original buffer now
    // If you didn't want an owned copy, you could use &WideCStr.
    LocalFree(buffer as HLOCAL);
}
// Convert to a regular Rust String and use it to your heart's desire!
let message = widestr.to_string_lossy();

Structs

MissingNulError	An error returned from WideCString and WideCStr to indicate that a terminating nul value was missing.
NulError	An error returned from WideCString to indicate that an invalid nul value was found.
WideCStr	C-style wide string reference for WideCString.
WideCString	An owned, mutable C-style "wide" string for windows FFI that is nul-aware and nul-terminated.
WideStr	Wide string reference for WideString.
WideString	An owned, mutable "wide" string for windows FFI that is not nul-aware.