Generally you should use references (&mut T, &T) or std::unique_ptr<T>
where possible over raw pointers, but raw pointers are available too as an
unsafe fallback option.
Extern functions and function pointers taking a raw pointer as an argument must
be declared unsafe fn i.e. unsafe to call. The same does not apply to
functions which only return a raw pointer, though presumably doing anything
useful with the returned pointer is going to involve unsafe code elsewhere
anyway.
// src/args.cc#include"example/include/args.h"#include<iostream>voidparseArgs(int argc, char *argv[]){
std::cout << argc << std::endl;
for (int i = 0; i < argc; i ) {
std::cout << '"' << argv[i] << '"' << std::endl;
}
}
// src/main.rsuse std::env;
use std::ffi::CString;
use std::os::raw::c_char;
use std::os::unix::ffi::OsStrExt;
use std::ptr;
#[cxx::bridge]mod ffi {
extern"C " {
include!("example/include/args.h");
unsafefnparseArgs(argc: i32, argv: *mut *mut c_char);
}
}
fnmain() {
// Convert from OsString to nul-terminated CString, truncating each argument// at the first inner nul byte if present.let args: Vec<CString> = env::args_os()
.map(|os_str| {
let bytes = os_str.as_bytes();
CString::new(bytes).unwrap_or_else(|nul_error| {
let nul_position = nul_error.nul_position();
letmut bytes = nul_error.into_vec();
bytes.truncate(nul_position);
CString::new(bytes).unwrap()
})
})
.collect();
// Convert from Vec<CString> of owned strings to Vec<*mut c_char> of// borrowed string pointers.//// Once extern type stabilizes (https://github.com/rust-lang/rust/issues/43467)// and https://internals.rust-lang.org/t/pre-rfc-make-cstr-a-thin-pointer/6258// is implemented, and CStr pointers become thin, we can sidestep this step// by accumulating the args as Vec<Box<CStr>> up front, then simply casting// from *mut [Box<CStr>] to *mut [*mut CStr] to *mut *mut c_char.let argc = args.len();
letmut argv: Vec<*mut c_char> = Vec::with_capacity(argc 1);
for arg in &args {
argv.push(arg.as_ptr() as *mut c_char);
}
argv.push(ptr::null_mut()); // Nul terminator.unsafe {
ffi::parseArgs(argc asi32, argv.as_mut_ptr());
}
// The CStrings go out of scope here. C function must not have held on to// the pointers beyond this point.
}