Enhance buffering and target stream handling of iostreams

- buffering may be independent of tied streams, so make it an extra param - the target output stream might be out, error or log The latter is important as cerr and clog share the underlying buffer which avoids mangled output. This is consistent with the stdlib implementation.
boostorg · Oct 18, 2024 · d7572e0 · d7572e0
1 parent 4f4b7ab
commit d7572e0
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Showing 3 changed files with 37 additions and 17 deletions.
diff --git a/include/boost/nowide/iostream.hpp b/include/boost/nowide/iostream.hpp
@@ -40,7 +40,13 @@ namespace nowide {
         class BOOST_NOWIDE_DECL winconsole_ostream : public std::ostream
         {
         public:
-            winconsole_ostream(bool isBuffered, winconsole_ostream* tieStream);
+            enum class target_stream
+            {
+                output,
+                error,
+                log,
+            };
+            winconsole_ostream(target_stream target, bool isBuffered, winconsole_ostream* tieStream);
             ~winconsole_ostream();
 
         private:

diff --git a/src/iostream.cpp b/src/iostream.cpp
@@ -82,27 +82,37 @@ namespace nowide {
             }
         };
 
-        winconsole_ostream::winconsole_ostream(const bool isBuffered, winconsole_ostream* tieStream) : std::ostream(0)
+        winconsole_ostream::winconsole_ostream(const target_stream target,
+                                               const bool isBuffered,
+                                               winconsole_ostream* tieStream) :
+            std::ostream(nullptr)
         {
-            HANDLE h;
-            if(isBuffered)
-                h = GetStdHandle(STD_OUTPUT_HANDLE);
-            else
-                h = GetStdHandle(STD_ERROR_HANDLE);
+            const HANDLE h = GetStdHandle(target == target_stream::output ? STD_OUTPUT_HANDLE : STD_ERROR_HANDLE);
+
             if(is_atty_handle(h))
             {
-                d.reset(new console_output_buffer(h));
-                std::ostream::rdbuf(d.get());
+                if(target == target_stream::log)
+                    rdbuf(boost::nowide::cerr.rdbuf()); // clog and cerr use the same buffer
+                else
+                {
+                    d.reset(new console_output_buffer(h));
+                    rdbuf(d.get());
+                }
             } else
             {
-                std::ostream::rdbuf(isBuffered ? std::cout.rdbuf() : std::cerr.rdbuf());
+                switch(target)
+                {
+                case target_stream::error: rdbuf(std::cerr.rdbuf()); break;
+                case target_stream::log: rdbuf(std::clog.rdbuf()); break;
+                case target_stream::output: rdbuf(std::cout.rdbuf()); break;
+                }
                 assert(rdbuf());
             }
+
             if(tieStream)
-            {
                 tie(tieStream);
-                setf(ios_base::unitbuf); // If tieStream is set, this is cerr -> set unbuffered
-            }
+            if(!isBuffered)
+                setf(ios_base::unitbuf);
         }
         winconsole_ostream::~winconsole_ostream()
         {
@@ -134,7 +144,7 @@ namespace nowide {
 
     } // namespace detail
 
-    // Make sure those are initialized as early as possible
+// Make sure those are initialized as early as possible
 #ifdef BOOST_MSVC
 #pragma warning(disable : 4073)
 #pragma init_seg(lib)
@@ -144,10 +154,11 @@ namespace nowide {
 #else
 #define BOOST_NOWIDE_INIT_PRIORITY
 #endif
-    detail::winconsole_ostream cout BOOST_NOWIDE_INIT_PRIORITY(true, nullptr);
+    using target_stream = detail::winconsole_ostream::target_stream;
+    detail::winconsole_ostream cout BOOST_NOWIDE_INIT_PRIORITY(target_stream::output, true, nullptr);
     detail::winconsole_istream cin BOOST_NOWIDE_INIT_PRIORITY(&cout);
-    detail::winconsole_ostream cerr BOOST_NOWIDE_INIT_PRIORITY(false, &cout);
-    detail::winconsole_ostream clog BOOST_NOWIDE_INIT_PRIORITY(false, nullptr);
+    detail::winconsole_ostream cerr BOOST_NOWIDE_INIT_PRIORITY(target_stream::error, false, &cout);
+    detail::winconsole_ostream clog BOOST_NOWIDE_INIT_PRIORITY(target_stream::log, true, nullptr);
 } // namespace nowide
 } // namespace boost
 

diff --git a/test/test_iostream.cpp b/test/test_iostream.cpp
@@ -245,6 +245,9 @@ void test_clog()
     if(usesNowideRdBufOut)                           // Only executed when attached to a real terminal, i.e. not on CI
         TEST(nw::clog.rdbuf() != std::clog.rdbuf()); // LCOV_EXCL_STOP
 
+    // Assumption:
+    TEST(std::clog.rdbuf() == std::cerr.rdbuf());
+
     TEST(nw::clog.rdbuf() != std::cout.rdbuf());
     TEST(nw::clog.rdbuf() != nw::cin.rdbuf());
     TEST(nw::clog.rdbuf() != nw::cout.rdbuf());