Struct libloading::Library[][src]

pub struct Library(_);
Expand description

A loaded dynamic library.


Find and load a dynamic library.

The filename argument may be any of:

  • A library filename;
  • Absolute path to the library;
  • Relative (to the current working directory) path to the library.

When a library is loaded initialization routines contained within the library are executed. For the purposes of safety, execution of these routines is conceptually the same calling an unknown foreign function and may impose arbitrary requirements on the caller for the call to be sound.

Additionally, the callers of this function must also ensure that execution of the termination routines contained within the library is safe as well. These routines may be executed when the library is unloaded.


The implementation strives to be as MT-safe as sanely possible, however on certain platforms the underlying error-handling related APIs not always MT-safe. This library shares these limitations on those platforms. In particular, on certain UNIX targets dlerror is not MT-safe, resulting in garbage error messages in certain MT-scenarios.

Calling this function from multiple threads is not MT-safe if used in conjunction with library filenames and the library search path is modified (SetDllDirectory function on Windows, {DY,}LD_LIBRARY_PATH environment variable on UNIX).

Platform-specific behaviour

When a plain library filename is supplied, locations where library is searched for is platform specific and cannot be adjusted in a portable manner. See documentation for the platform specific os::unix::Library::new and [os::windows::Library::new] methods for further information on library lookup behaviour.

If the filename specifies a library filename without path and with extension omitted, .dll extension is implicitly added on Windows.


Distributing your dynamic libraries under a filename common to all platforms (e.g. awesome.module) allows to avoid code which has to account for platform’s conventional library filenames.

Strive to specify an absolute or at least a relative path to your library, unless system-wide libraries are being loaded. Platform-dependent library search locations combined with various quirks related to path-less filenames may cause flakiness in programs.

// Any of the following are valid.
unsafe {
    let _ = Library::new("/path/to/awesome.module").unwrap();
    let _ = Library::new("../awesome.module").unwrap();
    let _ = Library::new("").unwrap();

Get a pointer to function or static variable by symbol name.

The symbol may not contain any null bytes, with an exception of last byte. Providing a null terminated symbol may help to avoid an allocation.

Symbol is interpreted as-is; no mangling is done. This means that symbols like x::y are most likely invalid.


Users of this API must specify the correct type of the function or variable loaded. Using a Symbol with a wrong type is undefined.

Platform-specific behaviour

Implementation of thread local variables is extremely platform specific and uses of such variables that work on e.g. Linux may have unintended behaviour on other targets.

On POSIX implementations where the dlerror function is not confirmed to be MT-safe (such as FreeBSD), this function will unconditionally return an error when the underlying dlsym call returns a null pointer. There are rare situations where dlsym returns a genuine null pointer without it being an error. If loading a null pointer is something you care about, consider using the os::unix::Library::get_singlethreaded call.


Given a loaded library:

let lib = unsafe {

Loading and using a function looks like this:

unsafe {
    let awesome_function: Symbol<unsafe extern fn(f64) -> f64> =

A static variable may also be loaded and inspected:

unsafe {
    let awesome_variable: Symbol<*mut f64> = lib.get(b"awesome_variable\0").unwrap();
    **awesome_variable = 42.0;

Unload the library.

This method might be a no-op, depending on the flags with which the Library was opened, what library was opened or other platform specifics.

You only need to call this if you are interested in handling any errors that may arise when library is unloaded. Otherwise the implementation of Drop for Library will close the library and ignore the errors were they arise.

The underlying data structures may still get leaked if an error does occur.

Trait Implementations

Formats the value using the given formatter. Read more

Performs the conversion.

Performs the conversion.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Performs the conversion.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.