CODEWITHSUNDEEP
pythonc++matrixrustffi
Chris
Chris

Reputation: 1

How can I pass a FFI array as a c_void pointer to nalgebra's DMatrix2?

I have a matrix in the form of an array in C++ and would like to pass it to a shared library function written in Rust. I have something like this

#![crate_type = "dylib"]

extern crate libc;
use libc::c_void;

extern crate nalgebra as na;
use na::DMatrix2;

#[no_mangle]
pub extern "C" fn rust_fn(p_data: *const c_void, sizex: usize, sizey: usize) {
    let matrix = DMatrix2::from_row_vector(sizey, sizex, p_data);
    // Do something usefull with the matrix
}

This doesn't compile since I pass a c_void to from_row_vector().

How can I do this right?

The matrix is an array of doubles, but I'm trying to keep the interface generic so I can also call the functions from e.g. Python.

I don't want to free the matrix when returning from the function (I want to borrow, not own the matrix).

Upvotes: 0

Views: 270

Answers (1)

oli_obk
oli_obk

Reputation: 31233

You can use std::slice::from_raw_parts to obtain a slice:

let slice = std::slice::from_raw_parts(p_data, sizex*sizey);

To make sure that the pointer types match up, you can either change p_data's type in the argument list to *const N where N is the type you use in the matrix, or use a cast like p_data as *const N.

Upvotes: 1

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