From 7ed2d982ac15df78e852fd5835d137881536a4ef Mon Sep 17 00:00:00 2001
From: Martin Pitt <martin@piware.de>
Date: Fri, 27 Aug 2021 11:08:54 +0200
Subject: [PATCH] Call Rust function from C: Skeleton

---
 .gitignore                  |  3 +++
 call-rust-from-c/Cargo.toml |  9 +++++++++
 call-rust-from-c/Makefile   | 20 ++++++++++++++++++++
 call-rust-from-c/src/lib.rs | 26 ++++++++++++++++++++++++++
 call-rust-from-c/src/main.c |  8 ++++++++
 5 files changed, 66 insertions(+)
 create mode 100644 call-rust-from-c/Cargo.toml
 create mode 100644 call-rust-from-c/Makefile
 create mode 100644 call-rust-from-c/src/lib.rs
 create mode 100644 call-rust-from-c/src/main.c

diff --git a/.gitignore b/.gitignore
index 7ecae2e..125ba96 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,6 @@ target
 libmount.rs
 c-langinfo
 c-mounts
+
+rustlib.h
+main
diff --git a/call-rust-from-c/Cargo.toml b/call-rust-from-c/Cargo.toml
new file mode 100644
index 0000000..2868470
--- /dev/null
+++ b/call-rust-from-c/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "call-rust-from-c"
+version = "0.1.0"
+edition = "2018"
+
+[lib]
+crate-type = ['staticlib']
+
+[dependencies]
diff --git a/call-rust-from-c/Makefile b/call-rust-from-c/Makefile
new file mode 100644
index 0000000..66a951a
--- /dev/null
+++ b/call-rust-from-c/Makefile
@@ -0,0 +1,20 @@
+RLIB = target/debug/libcall_rust_from_c.a
+
+main: src/main.o $(RLIB)
+	$(CC) -Wall -o $@ $^
+
+src/main.o: src/rustlib.h
+
+src/rustlib.h: src/lib.rs
+	cbindgen --lang c --output $@
+
+$(RLIB): src/lib.rs
+	cargo build
+
+run: main
+	./main
+
+check:
+	cargo test
+
+.PHONY: run test
diff --git a/call-rust-from-c/src/lib.rs b/call-rust-from-c/src/lib.rs
new file mode 100644
index 0000000..f5e4384
--- /dev/null
+++ b/call-rust-from-c/src/lib.rs
@@ -0,0 +1,26 @@
+use std::os::raw;
+
+/// Return The Answer.
+///
+/// # Example
+///
+/// ```
+/// let a = call_rust_from_c::answer();
+/// assert_eq!(a, 42);
+/// ```
+#[no_mangle]
+// C 'int'; it does not actually hurt to have more specific types such as int32_t, but it's good to know that plain ints work
+pub extern "C" fn answer() -> raw::c_int {
+    return 42;
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_answer() {
+        assert_eq!(answer(), 42);
+    }
+}
diff --git a/call-rust-from-c/src/main.c b/call-rust-from-c/src/main.c
new file mode 100644
index 0000000..b514433
--- /dev/null
+++ b/call-rust-from-c/src/main.c
@@ -0,0 +1,8 @@
+#include <stdio.h>
+#include "rustlib.h"
+
+int main()
+{
+    printf("The answer: %i\n", answer());
+    return 0;
+}
-- 
2.39.5