CODEWITHSUNDEEP
rustcompilationrust-cargo
NobinPegasus
NobinPegasus

Reputation: 787

Error while compiling a rust file generated by c2rust. using rustc

I have a rust program named hello.rs.

The program is I'm unable to compile it using rustc. I generated the hello.rs using c2rust online transpiler. But if I use cargo run hello.rs the program runs smoothly.

When using rustc it shows the following error. How to fix it?

The original hello.c file:

    void main() {
       // printf() displays the string inside quotation
       printf("Hello, World!");
       
    }

The hello.rs file.

    #![allow(dead_code, mutable_transmutes, non_camel_case_types, non_snake_case,
             non_upper_case_globals, unused_assignments, unused_mut)]
    #![register_tool(c2rust)]
    #![feature(main, register_tool)]
    extern "C" {
        #[no_mangle]
        fn printf(_: *const libc::c_char, _: ...) -> libc::c_int;
    }
    unsafe fn main_0() {
        // printf() displays the string inside quotation
        printf(b"Hello, World!\x00" as *const u8 as *const libc::c_char);
    }
    #[main]
    pub fn main() { unsafe { main_0() } ::std::process::exit(0i32); }

The error message:

┌──(pegasus㉿pegasus)-[~/Documents/Rust_testing]
└─$ rustc hello.rs -o test2
error[E0557]: feature has been removed
 --> hello.rs:4:12
  |
4 | #![feature(main, register_tool)]
  |            ^^^^ feature has been removed

error: cannot find attribute `main` in this scope
  --> hello.rs:13:3
   |
13 | #[main]
   |   ^^^^
   |
   = note: `main` is in scope, but it is a function, not an attribute

error[E0433]: failed to resolve: use of undeclared crate or module `libc`
 --> hello.rs:7:21
  |
7 | fn printf(_: *const libc::c_char, _: ...) -> libc::c_int;
  |                     ^^^^ use of undeclared crate or module `libc`

error[E0433]: failed to resolve: use of undeclared crate or module `libc`
 --> hello.rs:7:46
  |
7 | fn printf(_: *const libc::c_char, _: ...) -> libc::c_int;
  |                                              ^^^^ use of undeclared crate or module `libc`

error[E0433]: failed to resolve: use of undeclared crate or module `libc`
  --> hello.rs:11:52
   |
11 | printf(b"Hello, World!\x00" as *const u8 as *const libc::c_char);
   |                                                    ^^^^ use of undeclared crate or module `libc`

warning: `#[no_mangle]` has no effect on a foreign function
 --> hello.rs:6:1
  |
6 | #[no_mangle]
  | ^^^^^^^^^^^^ help: remove this attribute
7 | fn printf(_: *const libc::c_char, _: ...) -> libc::c_int;
  | --------------------------------------------------------- foreign function
  |
  = note: `#[warn(unused_attributes)]` on by default
  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
  = note: symbol names in extern blocks are not mangled

error: aborting due to 5 previous errors; 1 warning emitted

Some errors have detailed explanations: E0433, E0557.
For more information about an error, try `rustc --explain E0433`.

When using cargo it compiles and runs perfectly.

└─$ cargo run hello.rs                    
   Compiling Rust_testing v0.1.0 (/home/pegasus/Documents/Rust_testing)
warning: crate `Rust_testing` should have a snake case name
  |
  = note: `#[warn(non_snake_case)]` on by default
  = help: convert the identifier to snake case: `rust_testing`

warning: `Rust_testing` (bin "Rust_testing") generated 1 warning
    Finished dev [unoptimized + debuginfo] target(s) in 0.17s
     Running `target/debug/Rust_testing hello.rs`
Hello, world!

When removing the #[] this code runs in the playground.

here's the new.rs code:

extern "C" {
    fn printf(_: *const libc::c_char, _: ...) -> libc::c_int;
}
unsafe fn main_0() {
    // printf() displays the string inside quotation
    printf(b"Hello, World!\x00" as *const u8 as *const libc::c_char);
}
pub fn main() { unsafe { main_0() } ::std::process::exit(0i32); }

But it still shows the three error[E0433]: failed to resolve: use of undeclared crate or module libc.

Here's my Cargo.toml file:

[package]
name = "Rust_testing"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
libc = "0.2"

Upvotes: 0

Views: 846

Answers (1)

Finomnis
Finomnis

Reputation: 22818

It doesn't work for me either, even with cargo run. I'm unsure, maybe this requires an old version of nightly Rust?

Either way, if you remove the questionable code, it works without a problem:

extern "C" {
    fn printf(_: *const libc::c_char, _: ...) -> libc::c_int;
}

unsafe fn main_0() {
    // printf() displays the string inside quotation
    printf(b"Hello, World!\n\x00" as *const u8 as *const libc::c_char);
}

pub fn main() {
    unsafe { main_0() }
    ::std::process::exit(0i32);
}

Hello, World!

You mention that it doesn't work with rustc directly. That is true, because rustc is a compiler, it is not a dependency manager. You need to link the dependencies manually if you don't want to use cargo. I highly recommend using cargo, though.

If you run cargo run -vv (of course run cargo clean before, otherwise you won't see anything), you can see how cargo adds the dependencies.

Upvotes: 1

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