FFIing a C# char[][] into Rust

Asked Oct 16 '22 at 04:34

Active Oct 16 '22 at 13:21

Viewed 54 times

I'm trying to pass a char[][] to Rust, which then needs to decode it back to a String.

I've tried a few approaches:

Using Marshal to copy each array with a header of the array length, then reading it back in Rust.

I did this using Marshal.AllocHGlobal, but after the Rust code finished the C# crashes when I try to free the memory. (Same with Marshal.AllocCoTask).

Using GCAlloc to copy the array to unmanaged memory, then loading that

This SEGFAULTed. I don't know why, but I couldn't find enough documentation over GCAlloc to figure it out

Just passing the array to Rust

Between https://github.com/rust-lang/rust/issues/58905 and https://medium.com/jim-fleming/complex-types-with-rust-s-ffi-315d14619479, this route seemed ill-advised.

So what can I do to pass this dang array? The first approach works fine with a char[], and I've got no clue why it crashes (the memory pointers are actual pointers, not 0 also).

edited Oct 16 '22 at 13:21

Mohammad Aghazadeh

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asked Oct 16 '22 at 04:34

Big_Bad_E

What's a _char[][]_. Is it a `char[][]`. You may want to put a space between the brackets to emphasize that it's not a rectangle – Flydog57 Oct 16 '22 at 04:50
Rust's ffi is based on C's ABI. So you have to expose your C# types as C types in order to communicate with rust. – Aleksander Krauze Oct 16 '22 at 04:58
@Flydog57 A rectangle makes no sense, but I guess the font is weird. – Big_Bad_E Oct 16 '22 at 16:02
@AleksanderKrauze Yes, the point is you cannot do that with arrays to Rust, look at the 3rd approach I put. – Big_Bad_E Oct 16 '22 at 16:03

FFIing a C# char[][] into Rust

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