chore: move __c_cpp/* to __ffi

__ffi/c_export/Cargo.lock

@@ -0,0 +1,16 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "c_export"
+version = "0.1.0"
+dependencies = [
+ "libc 0.2.60 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "libc"
+version = "0.2.60"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[metadata]
+"checksum libc 0.2.60 (registry+https://github.com/rust-lang/crates.io-index)" = "d44e80633f007889c7eff624b709ab43c92d708caad982295768a7b13ca3b5eb"

__ffi/c_export/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "c_export"
+version = "0.1.0"
+authors = ["Hatter Jiang <jht5945@gmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[lib]
+name = "stringtools"
+crate-type = ["dylib"]
+
+[dependencies]
+libc = "0.2.60"

__ffi/c_export/README.md

@@ -0,0 +1,29 @@
+
+Rust libray build:
+```
+cargo build
+```
+
+
+Python test:
+```
+python call_in_python.py
+```
+
+
+C test:
+```
+gcc call_in_c.c -L target/debug/ -lstringtools
+```
+
+
+NodeJS test:
+```
+npm install ffi
+node call_in_node.js
+```
+
+
+Reference:
+http://siciarz.net/24-days-of-rust-calling-rust-from-other-languages/
+

__ffi/c_export/call_in_c.c

@@ -0,0 +1,9 @@
+#include <stdint.h>
+#include <stdio.h>
+
+int32_t count_substrings(const char* value, const char* substr);
+
+int main() {
+    printf("%d\n", count_substrings("banana", "na"));
+    return 0;
+}

__ffi/c_export/call_in_node.js

@@ -0,0 +1,8 @@
+var ffi = require('ffi');
+
+var stringtools = ffi.Library('target/debug/libstringtools.dylib', {
+    'count_substrings': ['int', ['string', 'string']]
+});
+
+console.log(stringtools.count_substrings("banana", "na"));
+

__ffi/c_export/call_in_python.py

@@ -0,0 +1,5 @@
+import ctypes
+
+stringtools = ctypes.CDLL("target/debug/libstringtools.dylib")
+print(stringtools.count_substrings(b"banana", b"na"))
+

__ffi/c_export/src/lib.rs

@@ -0,0 +1,17 @@
+extern crate libc;
+
+use std::ffi::CStr;
+use libc::c_char;
+
+#[no_mangle]
+pub extern "C" fn count_substrings(value: *const c_char, substr: *const c_char) -> i32 {
+    let c_value = unsafe { CStr::from_ptr(value) };
+    let c_substr = unsafe { CStr::from_ptr(substr) };
+    match c_value.to_str() {
+        Ok(value) => match c_substr.to_str() {
+            Ok(substr) => value.match_indices(substr).count() as i32,
+            Err(_) => -1,
+        },
+        Err(_) => -1,
+    }
+}