diff --git a/rust/trexio/src/exit_code.rs b/rust/trexio/src/exit_code.rs
index d842d34..74cc08d 100644
--- a/rust/trexio/src/exit_code.rs
+++ b/rust/trexio/src/exit_code.rs
@@ -93,7 +93,7 @@ impl ExitCode {
     }
 
     /// Conversion to a C value
-    pub fn to_c(self) -> c::trexio_exit_code  {
+    pub fn to_c(&self) -> c::trexio_exit_code  {
         match self {
             Self::Failure                =>  c::TREXIO_FAILURE,
             Self::Success                =>  c::TREXIO_SUCCESS,
@@ -136,4 +136,29 @@ impl ExitCode {
             Self::PhaseChange            =>  c::TREXIO_PHASE_CHANGE,
         }
     }
+
+    pub fn to_str(&self) -> Result<&'static str, Utf8Error> {
+        let c_error = self.to_c();
+        let c_buf: *const c_char = unsafe { c::trexio_string_of_error( c_error ) };
+        let c_str: &CStr = unsafe { CStr::from_ptr(c_buf) };
+        c_str.to_str()
+    }
+}
+
+use std::fmt;
+use std::error::Error;
+use std::ffi::CStr;
+use std::ffi::c_char;
+use std::str::Utf8Error;
+
+impl fmt::Display for ExitCode {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.to_str().unwrap())
+    }
+}
+
+impl Error for ExitCode {
+    fn description(&self) -> &str {
+        self.to_str().unwrap()
+    }
 }
diff --git a/rust/trexio/src/main.rs b/rust/trexio/src/main.rs
index 98fb1b2..bd80371 100644
--- a/rust/trexio/src/main.rs
+++ b/rust/trexio/src/main.rs
@@ -1,6 +1,8 @@
+use std::error::Error;
+
 mod test;
 
-fn main() {
+fn main() -> Result<(), Box<dyn Error>> {
         println!("============================================");
         println!("         TREXIO VERSION : {}", trexio::PACKAGE_VERSION );
         println!("============================================");
@@ -8,6 +10,7 @@ fn main() {
     let file_name = "test_write_rust.dir";
 
     let back_end = trexio::BackEnd::Text;
-    test::test_write(file_name, back_end);
+    test::test_write(file_name, back_end)?;
 
+    Ok(())
 }
diff --git a/rust/trexio/src/test.rs b/rust/trexio/src/test.rs
index 5380178..9dd253d 100644
--- a/rust/trexio/src/test.rs
+++ b/rust/trexio/src/test.rs
@@ -1,6 +1,6 @@
 use trexio::back_end::BackEnd;
 
-pub fn test_write(file_name: &str, back_end: BackEnd) {
+pub fn test_write(file_name: &str, back_end: BackEnd) -> Result<(), trexio::ExitCode> {
 
     // Prepare data to be written
     let n_buffers = 5;
@@ -56,32 +56,32 @@ pub fn test_write(file_name: &str, back_end: BackEnd) {
 
 
     println!("{}", file_name);
-    assert!( ! trexio::inquire(file_name).unwrap() );
+    assert!( ! trexio::inquire(file_name)? );
 
-    let trex_file = trexio::open(file_name, 'w', back_end).unwrap();
+    let trex_file = trexio::open(file_name, 'w', back_end)?;
 
-    assert!( ! trexio::has_nucleus(trex_file).unwrap() );
-    assert!( ! trexio::has_nucleus_num(trex_file).unwrap() );
-    assert!( ! trexio::has_nucleus_charge(trex_file).unwrap() );
-    assert!( ! trexio::has_ao_2e_int(trex_file).unwrap() );
-    assert!( ! trexio::has_ao_2e_int_eri(trex_file).unwrap() );
-    assert!( ! trexio::has_determinant_list(trex_file).unwrap() );
+    assert!( ! trexio::has_nucleus(trex_file)? );
+    assert!( ! trexio::has_nucleus_num(trex_file)? );
+    assert!( ! trexio::has_nucleus_charge(trex_file)? );
+    assert!( ! trexio::has_ao_2e_int(trex_file)? );
+    assert!( ! trexio::has_ao_2e_int_eri(trex_file)? );
+    assert!( ! trexio::has_determinant_list(trex_file)? );
 
-    trexio::write_nucleus_num(trex_file, nucleus_num).unwrap();
-    trexio::write_nucleus_charge(trex_file, charge).unwrap();
-    trexio::write_nucleus_point_group(trex_file, sym_str).unwrap();
-    trexio::write_nucleus_coord(trex_file, coord).unwrap();
-    trexio::write_nucleus_label(trex_file, label).unwrap();
-    trexio::write_basis_shell_num(trex_file, basis_shell_num).unwrap();
-    trexio::write_basis_nucleus_index(trex_file, basis_nucleus_index).unwrap();
-    trexio::write_state_id(trex_file, state_id).unwrap();
+    trexio::write_nucleus_num(trex_file, nucleus_num)?;
+    trexio::write_nucleus_charge(trex_file, charge)?;
+    trexio::write_nucleus_point_group(trex_file, sym_str)?;
+    trexio::write_nucleus_coord(trex_file, coord)?;
+    trexio::write_nucleus_label(trex_file, label)?;
+    trexio::write_basis_shell_num(trex_file, basis_shell_num)?;
+    trexio::write_basis_nucleus_index(trex_file, basis_nucleus_index)?;
+    trexio::write_state_id(trex_file, state_id)?;
 
-    if ! trexio::has_ao_num(trex_file).unwrap() {
-        trexio::write_ao_num(trex_file, ao_num).unwrap();
+    if ! trexio::has_ao_num(trex_file)? {
+        trexio::write_ao_num(trex_file, ao_num)?;
     }
 
-    if ! trexio::has_mo_num(trex_file).unwrap() {
-        trexio::write_mo_num(trex_file, mo_num).unwrap();
+    if ! trexio::has_mo_num(trex_file)? {
+        trexio::write_mo_num(trex_file, mo_num)?;
     }
 
     let mut energy = Vec::with_capacity(mo_num);
@@ -91,6 +91,6 @@ pub fn test_write(file_name: &str, back_end: BackEnd) {
     }
     println!("{:#?}", energy);
 
-    trexio::close(trex_file).expect("Unable to close File");
+    trexio::close(trex_file)
 
 }