reprC

reprC is an attribute used in the Rust programming language to designate that a struct or union should have a memory layout compatible with the C programming language. By applying this attribute, Rust ensures that the data layout, including field order and padding, follows the rules of the C ABI on the target platform. This makes it possible to interface Rust code with C libraries through the Foreign Function Interface (FFI).

Usage and behavior: The attribute is placed on a type definition, typically as #[repr(C)]. This signals the compiler to lay out the type in a way that aligns with a corresponding C struct. It is commonly used for structs and unions that will be passed to or from C functions, ensuring that Rust and C agree on how data is arranged in memory. It can be combined with other layout-related options, such as #[repr(C, packed)], to alter alignment and padding, though packing can introduce performance and safety trade-offs.

Example:

#[repr(C)]

struct Point {

x: f64,

y: f64,

}

Limitations and considerations: repr(C) provides a C-compatible layout but is not a guarantee of complete ABI compatibility across all platforms or compilers. Developers must ensure that both sides of an FFI boundary agree on type sizes and representations, often by using standard C types or fixed-width integers from libc or std::os::raw. Endianness, alignment requirements, and structure padding can still vary by platform. Additionally, repr(C) does not make a type inherently safe for FFI; unsafe blocks and explicit validation are still required when exchanging data with C code.

In summary, repr(C) is a Rust feature for enabling C-compatible data layouts to facilitate safe and predictable interoperability with C libraries.