QGlobal: Define a default message handler

Currently, qInstallMsgHandler() does not return the
handle to the default message handler. This patch defines
a default message handler. This is returned by
qInstallMsgHandler() when called for the first time. A call
to qInstallMsgHandler(0) will restore the default message
handler as was the case previously.

Change-Id: I42f06654d45fb0e633f3c6d912fc8f05c23249aa
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 38 insertions, 16 deletions

diff --git a/src/corelib/global/qglobal.cpp b/src/corelib/global/qglobal.cpp
index 453c4a96a8..91ac521a0b 100644
--- a/src/corelib/global/qglobal.cpp
+++ b/src/corelib/global/qglobal.cpp
@@ -2026,25 +2026,11 @@ extern bool usingWinMain;
 extern Q_CORE_EXPORT void qWinMsgHandler(QtMsgType t, const char* str);
 #endif
 
-QtMsgHandler qInstallMsgHandler(QtMsgHandler h)
-{
-    QtMsgHandler old = handler;
-    handler = h;
-#if defined(Q_OS_WIN) && defined(QT_BUILD_CORE_LIB)
-    if (!handler && usingWinMain)
-        handler = qWinMsgHandler;
-#endif
-    return old;
-}
-
 /*!
     \internal
 */
-void qt_message_output(QtMsgType msgType, const char *buf)
+static void qDefaultMsgHandler(QtMsgType, const char *buf)
 {
-    if (handler) {
-        (*handler)(msgType, buf);
-    } else {
 #if defined(Q_CC_MWERKS) && defined(Q_OS_MACX)
         mac_default_handler(buf);
 #elif defined(Q_OS_WINCE)
@@ -2067,7 +2053,31 @@ void qt_message_output(QtMsgType msgType, const char *buf)
         fprintf(stderr, "%s\n", buf);
         fflush(stderr);
 #endif
-    }
+}
+
+QtMsgHandler qInstallMsgHandler(QtMsgHandler h)
+{
+    //if handler is 0, set it to the
+    //default message handler
+    if (!handler)
+        handler = qDefaultMsgHandler;
+    QtMsgHandler old = handler;
+    handler = h;
+#if defined(Q_OS_WIN) && defined(QT_BUILD_CORE_LIB)
+    if (!handler && usingWinMain)
+        handler = qWinMsgHandler;
+#endif
+    return old;
+}
+
+/*!
+    \internal
+*/
+void qt_message_output(QtMsgType msgType, const char *buf)
+{
+    if (!handler)
+        handler = qDefaultMsgHandler;
+     (*handler)(msgType, buf);
 
     if (msgType == QtFatalMsg
         || (msgType == QtWarningMsg
diff --git a/tests/auto/corelib/io/qdebug/tst_qdebug.cpp b/tests/auto/corelib/io/qdebug/tst_qdebug.cpp
index 772fd9fd04..f33a7eef5a 100644
--- a/tests/auto/corelib/io/qdebug/tst_qdebug.cpp
+++ b/tests/auto/corelib/io/qdebug/tst_qdebug.cpp
@@ -54,6 +54,7 @@ private slots:
     void debugWithQBool() const;
     void veryLongWarningMessage() const;
     void qDebugQStringRef() const;
+    void defaultMessagehandler() const;
 };
 
 void tst_QDebug::assignment() const
@@ -154,5 +155,16 @@ void tst_QDebug::qDebugQStringRef() const
     }
 }
 
+void tst_QDebug::defaultMessagehandler() const
+{
+    QtMsgHandler defaultMessageHandler1 = qInstallMsgHandler(0);
+    QtMsgHandler defaultMessageHandler2 = qInstallMsgHandler(myMessageHandler);
+    bool same = (*defaultMessageHandler1 == *defaultMessageHandler2);
+    QVERIFY(same);
+    QtMsgHandler messageHandler = qInstallMsgHandler(0);
+    same = (*messageHandler == *myMessageHandler);
+    QVERIFY(same);
+}
+
 QTEST_MAIN(tst_QDebug);
 #include "tst_qdebug.moc"