Fix missing C stderr output (fprintf(stderr, ...) not shown) (#402)

Author: anutosh491

src/xinterpreter.cpp

@@ -56,16 +56,22 @@ using namespace std::placeholders;
 namespace xcpp
 {
     struct StreamRedirectRAII {
-      std::string &err;
-      StreamRedirectRAII(std::string &e) : err(e) {
-        Cpp::BeginStdStreamCapture(Cpp::kStdErr);
-        Cpp::BeginStdStreamCapture(Cpp::kStdOut);
-      }
-      ~StreamRedirectRAII() {
-        std::string out = Cpp::EndStdStreamCapture();
-        err = Cpp::EndStdStreamCapture();
-        std::cout << out;
-      }
+        std::string& out;
+        std::string& err;
+
+        StreamRedirectRAII(std::string& o, std::string& e)
+            : out(o)
+            , err(e)
+        {
+            Cpp::BeginStdStreamCapture(Cpp::kStdOut);
+            Cpp::BeginStdStreamCapture(Cpp::kStdErr);
+        }
+
+        ~StreamRedirectRAII()
+        {
+            err = Cpp::EndStdStreamCapture();
+            out = Cpp::EndStdStreamCapture();
+        }
     };
 
     void interpreter::configure_impl()
@@ -163,11 +169,12 @@ __get_cxx_version ()
         }
 
         std::string err;
+        std::string out;
 
         // Attempt normal evaluation
         try
         {
-            StreamRedirectRAII R(err);
+            StreamRedirectRAII R(out, err);
             compilation_result = Cpp::Process(code.c_str());
         }
         catch (std::exception& e)
@@ -182,11 +189,12 @@ __get_cxx_version ()
             ename = "Error: ";
         }
 
-        if (compilation_result)
+        if (!out.empty())
+        {
+            std::cout << out;
+        }
+        if (!err.empty())
         {
-            errorlevel = 1;
-            ename = "Error: ";
-            evalue = "Compilation error! " + err;
             std::cerr << err;
         }
 
@@ -201,6 +209,13 @@ __get_cxx_version ()
             std::cerr.rdbuf(cerr_strbuf);
         }
 
+        if (compilation_result)
+        {
+            errorlevel = 1;
+            ename = "Error: ";
+            evalue = "Compilation error! " + err;
+        }
+
         // Depending of error level, publish execution result or execution
         // error, and compose execute_reply message.
         if (errorlevel)

test/test_interpreter.cpp

@@ -1094,3 +1094,45 @@ TEST_SUITE("mime_bundle_repr")
         REQUIRE(res == expected);
     }
 }
+
+TEST_CASE("C and C++ stdout/stderr capture") 
+{
+    std::vector<const char*> Args = {};
+    xcpp::interpreter interpreter((int)Args.size(), Args.data());
+
+    xeus::execute_request_config config;
+    config.silent = false;
+    config.store_history = false;
+    config.allow_stdin = false;
+
+    nl::json header = nl::json::object();
+    xeus::xrequest_context::guid_list id = {};
+    xeus::xrequest_context context(header, id);
+
+    std::promise<nl::json> promise;
+    auto callback = [&promise](nl::json result) { promise.set_value(result); };
+
+    // Redirect std::cout and std::cerr
+    StreamRedirectRAII cout_redirect(std::cout);
+    StreamRedirectRAII cerr_redirect(std::cerr);
+
+    std::string code = R"(
+        #include <stdio.h>
+        #include <iostream>
+        printf("C stdout\n");
+        fprintf(stderr, "C stderr\n");
+        std::cout << "C++ stdout\n";
+        std::cerr << "C++ stderr\n";
+    )";
+
+    interpreter.execute_request(context, callback, code, config, nl::json::object());
+    (void)promise.get_future().get(); // wait for result
+
+    std::string captured_out = cout_redirect.getCaptured();
+    std::string captured_err = cerr_redirect.getCaptured();
+
+    REQUIRE(captured_out.find("C stdout") != std::string::npos);
+    REQUIRE(captured_out.find("C++ stdout") != std::string::npos);
+    REQUIRE(captured_err.find("C stderr") != std::string::npos);
+    REQUIRE(captured_err.find("C++ stderr") != std::string::npos);
+}