From c3336470788ed31670b578237fd49f2923c15df6 Mon Sep 17 00:00:00 2001
From: Tilman Blumhagen <tilman.blumhagen@googlemail.com>
Date: Fri, 19 May 2023 14:47:58 +0200
Subject: [PATCH] iiopp: exceptions now have a specific type, derived from
 std::system_error

std::system_error is better at reporting errno-based errors: It also
reports the error code while runtime_error only reported a message.

Also throwing a specific iiopp::error class allows applications to
discriminate them from other kinds of errors.

Signed-off-by: Tilman Blumhagen <tilman.blumhagen@googlemail.com>
---
 bindings/cpp/examples/iiopp-enum.cpp |  4 ++--
 bindings/cpp/iiopp.h                 | 15 ++++++++++-----
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/bindings/cpp/examples/iiopp-enum.cpp b/bindings/cpp/examples/iiopp-enum.cpp
index 5f4388305..19eb46eb5 100644
--- a/bindings/cpp/examples/iiopp-enum.cpp
+++ b/bindings/cpp/examples/iiopp-enum.cpp
@@ -93,9 +93,9 @@ int main(int argc, char ** argv)
     {
         enumerateIioEntities();
     }
-    catch (std::exception & e)
+    catch (error & e)
     {
-        cerr << "ERROR: " << e.what() << endl;
+        cerr << "ERROR " << e.code().value() << ": " << e.what() << endl;
         return EXIT_FAILURE;
     }
 
diff --git a/bindings/cpp/iiopp.h b/bindings/cpp/iiopp.h
index 6a5cc3ffb..983d2ecbe 100644
--- a/bindings/cpp/iiopp.h
+++ b/bindings/cpp/iiopp.h
@@ -18,7 +18,7 @@
 #include <string>
 #include <optional>
 #include <stdexcept>
-#include <sstream>
+#include <system_error>
 #include <cassert>
 #include <memory>
 
@@ -70,6 +70,14 @@ class cstr
     operator char const * () const {return s;}
 };
 
+/** @brief Thrown to report errors.
+ */
+class error : public std::system_error
+{
+public:
+    using std::system_error::system_error;
+};
+
 /** @brief Common interface for attribute access
  */
 class IAttr
@@ -123,10 +131,7 @@ inline std::string err_str(int err)
 [[noreturn]] inline void err(int err, char const * ctx)
 {
     assert(err > 0);
-    std::ostringstream s;
-    s << ctx << ": " << err_str(err);
-    s.flush();
-    throw std::runtime_error(s.str());
+    throw error(err, std::generic_category(), ctx);
 }
 
 inline void check(int ret, char const * ctx)