How to set QFile file name with path with windows separators "\"?

[freely]

Hello,
When I try to create new file in directory ( that has such permissions ) on Linux it works ok but on Windows I get the errors ( file.errorString() = "The parameter is incorrect" ) , file.error = 5 ):

QFile file(outputDir_+"/"+fileName);
     if (!file.open(QFile::WriteOnly))
         {
             QMessageBox::warning(0,"Could not create Project File",
                                        QObject::tr( "\n Could not create Project File on disk"));
 
                  return false;
         }

QFile file(outputDir_+"/"+fileName);
     if (!file.open(QFile::WriteOnly))
         {
             QMessageBox::warning(0,"Could not create Project File",
                                        QObject::tr( "\n Could not create Project File on disk"));

                  return false;
         }

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In Qt docs it is written that Qt 4.> automatically translates file name with path to such that contains separators for underlying system ( Linux - "/" , Windows - "\" ) and it is enought to pass to QFile constructor path with "/" separators , but when I call file.fileName() on Windows I get the "/" separators, another worlds how to create new file on windows?
Can anybody help/point what is the problem? Can anybody provide code snippet to create QFile on Windows? What to pass to QFile constructor as file name?
Thanks in advance.