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stringstaticrustffi

How do I create static C strings?


I want to create a plugin module (shared lib) in Rust that exports a C compatible structure containing static C strings. In Sept 2014, this Stack Overflow question determined it wasn't possible. As of Jan 2015 this still was not possible as per this Reddit thread. Has anything changed since?


Solution

  • The following seems to do the trick. I don't really want the struct to be mutable, but I get core::marker::Sync errors if I don't mark it as mut.

    extern crate libc;
    
    use libc::funcs::c95::stdio::puts;
    use std::mem;
    
    pub struct Mystruct {
        s1: *const u8,
        s2: *const u8,
    }
    
    const CONST_C_STR: *const u8 = b"a constant c string\0" as *const u8;
    
    #[no_mangle]
    pub static mut mystaticstruct: Mystruct = Mystruct {
        s1: CONST_C_STR,
        s2: b"another constant c string\0" as *const u8
    };
    
    fn main() {
        unsafe{
            puts(mystaticstruct.s1 as *const i8); // puts likes i8
            puts(mystaticstruct.s2 as *const i8);
            println!("Mystruct size {}", mem::size_of_val(&mystaticstruct));
        }
    }
    

    The output (on 64 bit linux) is ...

    a constant c string
    another constant c string
    Mystruct size 16