Improvement of WARN_LOGFILE possibilities

Improvement of the error / warning handling output in respect to the output file used:
- warning when the specified cannot be opened
- possibility to write warnings to stdout instead of the default stderr (useful for redirecting output on, especially, windows so output will not be "garbled").

Author: albert-github

Diff for: src/config.xml

@@ -1366,7 +1366,10 @@ FILE_VERSION_FILTER = "cleartool desc -fmt \%Vn"
 <![CDATA[
  The \c WARN_LOGFILE tag can be used to specify a file to which warning
  and error messages should be written. If left blank the output is written
- to standard error (`stderr`).
+ to standard error (`stderr`). In case the file specified cannot be opened for
+ writing the warning and error messages are written to standard error. When as 
+ file `-` is specified the warning and error messages are written to standard output
+ (`stdout`).
 ]]>
       </docs>
     </option>

Diff for: src/message.cpp

@@ -42,12 +42,22 @@ static std::mutex g_mutex;
 void initWarningFormat()
 {
   outputFormat = Config_getString(WARN_FORMAT);
+  QCString logFile = Config_getString(WARN_LOGFILE);
 
-  if (!Config_getString(WARN_LOGFILE).isEmpty())
+  if (!logFile.isEmpty())
   {
-    warnFile = Portable::fopen(Config_getString(WARN_LOGFILE),"w");
+    if (logFile == "-")
+    {
+      warnFile = stdout;
+    }
+    else if (!(warnFile = Portable::fopen(logFile,"w")))
+    {
+      // point it to something valid, because warn() relies on it
+      warnFile = stderr;
+      err("Cannot open '%s' for writing, redirecting 'WARN_LOGFILE' output to 'stderr'\n",logFile.data());
+    }
   }
-  if (!warnFile) // point it to something valid, because warn() relies on it
+  else
   {
     warnFile = stderr;
   }