concat two strings using raw poitners

concat-string.rs

extern crate nix;

use std::ffi::CString;
use std::ptr::write;

use nix::libc::{free, malloc, strlen};

fn main() {
    let c_str1 = CString::new("Hello, ").unwrap();
    let c_str2 = CString::new("world!").unwrap();

    let str1_ptr = c_str1.into_raw();
    let str2_ptr = c_str2.into_raw();

    let str1_len = unsafe { strlen(str1_ptr) };
    let str2_len = unsafe { strlen(str2_ptr) };

    let a_ptr = unsafe { malloc(str1_len + str2_len + 1) };
    let a = a_ptr as *mut i8;

    for i in 0..str1_len {
        unsafe { write(a.add(i), *(str1_ptr.add(i))) };
    }

    for i in 0..str2_len {
        unsafe { write(a.add(str1_len).add(i), *(str2_ptr.add(i))) };
    }

    let hello = unsafe { CString::from_raw(a) };

    println!("{}", hello.to_str().unwrap());

    unsafe { free(a_ptr) };
}