Calling c function with string

help
17

Thanks a lot, deeply appreciate your support :slight_smile:

Now the working code became like this:
The c file:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void c_free_string(const char *str){
    free(str);
}

char *concat(const char *str1, const char *str2)
{
    char *res;
    const char del[] = ", ";
    res = malloc(strlen(str1) + strlen(str2) + strlen(del) + 1);
    if (!res) {
        fprintf(stderr, "malloc() failed: insufficient memory!\n");
        return EXIT_FAILURE;
    }

    strcpy(res, str1);
    strcat(res, del);
    strcat(res, str2);

    printf("Result: '%s'\n", res);
    return res;
}

The Rust file:

use std::ffi::{CStr, CString};
use std::os::raw::c_char;
use std::ops::Deref;
use std::fmt;

extern "C" {
    fn concat(str1: *const c_char, str2: *const c_char) -> *mut c_char;
    fn c_free_string(str: *mut c_char);
}

pub struct Concat(*mut c_char);
impl fmt::Debug for Concat {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        CStr::fmt(self, f)
    }
}
impl Drop for Concat {
    fn drop(&mut self) {
        unsafe { c_free_string(self.0) }
    }
}
impl Deref for Concat {
    type Target = CStr;

    fn deref(&self) -> &CStr {
        unsafe { CStr::from_ptr(self.0) }
    }
}

fn concat_cstr(str1: &CStr, str2: &CStr) -> Concat {
    let concated = unsafe { concat(str1.as_ptr(), str2.as_ptr()) };
    Concat(concated)
}

fn main() {
    let str1  = CString::new("First").unwrap();
    let str2 = CString::new("Second").unwrap();
    let concated_string = concat_cstr(str1.as_c_str(), str2.as_c_str());
    println!("{:?}", concated_string.to_str());
}
4 Likes