FFI example from book cannot find -lanneclib under Windows

Question

Error linking following the external c dll with call back example.

I have created anneclib.dll and scattered it ( and the lib) have even tried full path but still get the same error ( but with the full path) .

Error 1 error: linking with gcc failed: exit code: 1 note: "gcc" "-Wl,--enable-long-section-names" "-fno-use-linker-plugin" "-Wl,--nxcompat" "-static-libgcc" "-m64" "-L" "C:\Program Files\Rust stable 1.0\bin\rustlib\x86_64-pc-windows-gnu\lib" "-o" "obj\Debug\Anne.exe" "obj\Debug\Anne.o" "-Wl,--gc-sections" "C:\Program Files\Rust stable 1.0\bin\rustlib\x86_64-pc-windows-gnu\lib\libstd-4e7c5e5c.rlib" "C:\Program Files\Rust stable 1.0\bin\rustlib\x86_64-pc-windows-gnu\lib\libcollections-4e7c5e5c.rlib" "C:\Program Files\Rust stable 1.0\bin\rustlib\x86_64-pc-windows-gnu\lib\libunicode-4e7c5e5c.rlib" "C:\Program Files\Rust stable 1.0\bin\rustlib\x86_64-pc-windows-gnu\lib\librand-4e7c5e5c.rlib" "C:\Program Files\Rust stable 1.0\bin\rustlib\x86_64-pc-windows-gnu\lib\liballoc-4e7c5e5c.rlib" "C:\Program Files\Rust stable 1.0\bin\rustlib\x86_64-pc-windows-gnu\lib\liblibc-4e7c5e5c.rlib" "C:\Program Files\Rust stable 1.0\bin\rustlib\x86_64-pc-windows-gnu\lib\libcore-4e7c5e5c.rlib" "-L" "C:\Program Files\Rust stable 1.0\bin\rustlib\x86_64-pc-windows-gnu\lib" "-L" "C:\src\ann\anne.rust\anne.rust\Anne.rust\bin\x86_64-pc-windows-gnu" "-L" "C:\src\ann\anne.rust\anne.rust\Anne\bin\x86_64-pc-windows-gnu" "-Wl,--whole-archive" "-Wl,-Bstatic" "-Wl,--no-whole-archive" "-Wl,-Bdynamic" "-lanneclib" "-lws2_32" "-luserenv" "-lcompiler-rt" note: ld: cannot find -lanneclib

Using the Visual Studio Rust project.

Where should I put it ?

extern fn callback(a: i32) {
    println!("I'm called from C with value {0}", a);
}

#[link(name = "anneclib")]
extern {
   fn register_callback(cb: extern fn(i32)) -> i32;
   fn trigger_callback();
}

fn main() {
    unsafe {
        register_callback(callback);
        trigger_callback(); // Triggers the callback
    }
}

Answer 1

In the error message you can see that the folder [your source folder]\bin\x86_64-pc-windows-gnu is added to the library path. You have to put your library into this folder. You may also have to add a 'lib' prefix to the library name.

Here is a small example that works for me:

A C file with a hello-function:

#include <stdio.h>

void hello() {
    printf("Hello from C!\n");
}

Compile the C file to a shared library libhello.c using MinGW:

gcc -shared -o libhello.dll hello.c

The Rust file main.rs:

#[link(name = "hello")]
extern {
    fn hello();
}

fn main() {
    unsafe { hello(); }
}

Now you have to put (a copy of) the libhello.dll into the sub-folder \bin\x86_64-pc-windows-gnu:

+ bin
+ --- x86_64-pc-windows-gnu
      + --- libhello.dll
+ main.rs

And you should be able to compile it via

rustc main.rs

Note in order to execute the main.exe you also need a copy of the libhello.dll next to the main.exe or in the system path.