Extern "C"
In Rust, extern "C" specifies the C calling convention for functions and foreign-function interfaces.
Refactoring to Rust
extern "C" is a Rust function annotation that gives a function the C ABI and makes it callable according to C conventions.
- How it is used
- Connects Rust functions to C handlers and callbacks across an FFI boundary.
- How deep it goes
- Explains calling conventions and annotation combinations, then demonstrates handlers and function-pointer types without detailing ABI internals.
- Examples
- Uses an NGINX request handler, a request-body callback, and a Rust-only request-body conversion helper.
- What you can do after
- Apply it to declare Rust functions callable from C and to type callbacks passed through C APIs.
Rust in Action: Systems programming concepts and techniques
extern "C" is Rust syntax that specifies C-compatible calling and linkage conventions for functions or foreign-function interfaces.
- How it is used
- Sets C calling conventions for a kernel entry point and declares externally provided LLVM functions.
- How deep it goes
- Explains the calling-convention purpose and shows both function and block syntax, without detailing argument layout.
- Examples
- Shows a kernel `_start` function and declarations for LLVM setjmp and longjmp intrinsics.
- What you can do after
- Apply it to a kernel entry point or external function declarations while distinguishing calling conventions from symbol names.
Read how Rust in Action: Systems programming concepts and techniques explains extern "C" →
Related concepts
- calling conventionuses · A calling convention is a set of platform-specific binary-interface rules governing how functions receive arguments, return values, preserve state, and manage calls.
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