rust: Use c_char for ffi.

rust/onnxruntime/src/lib.rs

@@ -151,6 +151,8 @@ to download.
 //! See the [`sample.rs`](https://github.com/nbigaouette/onnxruntime-rs/blob/main/onnxruntime/examples/sample.rs)
 //! example for more details.
 
+use std::ffi::c_char;
+
 use onnxruntime_sys as sys;
 
 // Make functions `extern "stdcall"` for Windows 32bit.
@@ -187,7 +189,7 @@ use sys::OnnxEnumInt;
 // Re-export ndarray as it's part of the public API anyway
 pub use ndarray;
 
-fn char_p_to_string(raw: *const i8) -> Result<String> {
+fn char_p_to_string(raw: *const c_char) -> Result<String> {
     let c_string = unsafe { std::ffi::CStr::from_ptr(raw as *mut i8).to_owned() };
 
     match c_string.into_string() {
@@ -201,7 +203,7 @@ mod onnxruntime {
     //! Module containing a custom logger, used to catch the runtime's own logging and send it
     //! to Rust's tracing logging instead.
 
-    use std::ffi::CStr;
+    use std::ffi::{CStr, c_char};
     use tracing::{debug, error, info, span, trace, warn, Level};
 
     use onnxruntime_sys as sys;
@@ -240,10 +242,10 @@ mod onnxruntime {
         pub(crate) fn custom_logger(
             _params: *mut std::ffi::c_void,
             severity: sys::OrtLoggingLevel,
-            category: *const i8,
-            logid: *const i8,
-            code_location: *const i8,
-            message: *const i8,
+            category: *const c_char,
+            logid: *const c_char,
+            code_location: *const c_char,
+            message: *const c_char,
         ) {
             let log_level = match severity {
                 sys::OrtLoggingLevel::ORT_LOGGING_LEVEL_VERBOSE => Level::TRACE,