Returning a String from Rust function to Python

Question

I\'m very new to Rust. How would I return a String from a Rust function that can be used in Python?

Here is my Rust implementation:

use          


        

Answer 1

The problem here is that you are returning a CString directly, which does not correspond to the representation of a string in C (you can see here the source code of CString).

You should be returning a pointer to the string, by using s.as_ptr(). However, you need to make sure that the string is not deallocated at the end of the function, since that would result in a dangling pointer.

The only solution I can think of is to use forget to let rust forget the variable instead of freeing it. Of course you will need to find a way to free the string later to avoid a memory leak (see Vladimir's answer).

With the changes I mentioned, your Rust code should be the following:

use std::ffi::CString;
use std::mem;

#[no_mangle]
pub extern fn query() -> *const i8 {
    let s = CString::new("Hello!").unwrap();
    let ptr = s.as_ptr();
    mem::forget(s);
    return ptr;
}