c++ - 如何从Rust调用C++动态库？

Question

我想从Rust调用一个C++动态库(* .so)，但是我不想从Rust构建它。像这样，

cc::Build::new()
    .file("src/foo.cc")
    .shared_flag(true)
    .compile("libfoo.so");

在某些情况下，我只需要调用几个函数，而不是所有函数。我该如何使用？

Answer 1

在继续之前，请确保您具有Rust FFI (foreign function interface)的基本概念。
在Rust中，调用C很容易，但是调用C++却很困难。
要在Rust中调用C函数，您只需要用extern包装它们，进行一些基本的类型转换，有时还需要unsafe。
要调用C++函数，由于Rust没有内置的C++功能知识，您可能需要做很多手动翻译。例如，这是Rust-Qt的文档的一部分:

Many things are directly translated from C++ to Rust:

• Primitive types are mapped to Rust's primitive types (like bool) and types provided by libc crate (like libc::c_int).
• Fixed-size numeric types (e.g int8_t or qint8) are mapped to Rust's fixed size types (e.g. i8).
• Pointers, references and values are mapped to Rust's respective types.
• C++ namespaces are mapped to Rust submodules.
• C++ classes and structs are mapped to Rust structs. This also applies to all instantiations of template classes encountered in thelibrary's API, including template classes of dependencies.
• Free functions are mapped to free functions.
• Class methods are mapped to structs' implementations.
• Destructors are mapped to Drop and CppDeletable implementations.
• Function pointer types are mapped to Rust's equivalent representation. Function pointers with references or class values arenot supported.
• static_cast and dynamic_cast are available in Rust through corresponding traits.

Names of Rust identifiers are modified according to Rust's namingconventions.

When direct translation is not possible:

• Contents of each include file of the C++ library are placed into a separate submodule.
• Method overloading is emulated with wrapping arguments in a tuple and creating a trait describing tuples acceptable by each method.Methods with default arguments are treated in the same way.
• Single inheritance is translated to Deref and DerefMut implementation, allowing to call base class methods on derivedobjects. When deref coercions are not enough, static_cast should beused to convert from derived to base class.
• Getter and setter methods are created for each public class field.

Not implemented yet but planned:

• Translate C++ typedefs to Rust type aliases.
• Implement operator traits for structs based on C++ operator methods (issue). Operatorsare currently exposed as regular functions with op_ prefix.
• Implement Debug and Display traits for structs if applicable methods exist on C++ side.
• Implement iterator traits for collections.
• Subclassing API (issue).
• Provide access to a class's public variables (issue).
• Provide conversion from enums to int and back (used in Qt API).
• Support C++ types nested into template types, like Class1<T>::Class2.

Not planned to support:

• Advanced template usage, like types with integer template arguments.
• Template partial specializations.
• Template methods and functions.

我的建议是将C++库包装为C库，然后将其称为正式FFI方式，或使用 rust-bindgen自动进行包装。
如果您仍然想在Rust中调用C++， rustcxx似乎是一个方便的工具。
关于库链接，这很简单:

将库放入系统库中，以搜索/usr/lib或/usr/local/lib/之类的路径，并确保可以通过ldconfig -p找到它。

或使用环境变量LD_LIBRARY_PATH来指定从CLI运行cargo时库所在的路径。