Padding filenames for ExodusII writer based on number of processes

In order to read in ExodusII files written out in parallel we
need to pad the process ids with zeros so that all of them are
associated together.

IO/Exodus/vtkExodusIIWriter.cxx

@@ -49,12 +49,23 @@
 #include <cctype>
 #include <map>
 #include <ctime>
-
-
+#include <sstream>
 
 vtkObjectFactoryNewMacro (vtkExodusIIWriter);
 vtkCxxSetObjectMacro (vtkExodusIIWriter, ModelMetadata, vtkModelMetadata);
 
+namespace
+{
+unsigned int GetNumberOfDigits(unsigned int i)
+{
+  if (i<10)
+  {
+    return 1;
+  }
+  return GetNumberOfDigits(i/10)+1;
+}
+}
+
 //----------------------------------------------------------------------------
 
 vtkExodusIIWriter::vtkExodusIIWriter ()
@@ -595,24 +606,25 @@ int vtkExodusIIWriter::CreateNewExodusFile()
   }
   else
   {
-    char *myFileName = new char [VTK_MAXPATH];
-    if (this->CurrentTimeIndex == 0)
-    {
-      sprintf(myFileName, "%s.%d.%d", this->FileName, this->NumberOfProcesses, this->MyRank);
-    }
-    else
+    std::ostringstream myFileName;
+    myFileName << this->FileName << ".";
+    if (this->CurrentTimeIndex != 0)
     {
-      sprintf(myFileName, "%s_%06d.%d.%d",
-          this->FileName, this->CurrentTimeIndex, this->NumberOfProcesses, this->MyRank);
+      myFileName << "_" << std::setfill('0') << std::setw(6) <<
+        this->CurrentTimeIndex << std::setw(0) << ".";
     }
-    this->fid = ex_create(myFileName, EX_CLOBBER, &compWordSize, &IOWordSize);
+    unsigned int numDigits = GetNumberOfDigits(
+      static_cast<unsigned int>(this->NumberOfProcesses-1));
+    myFileName << this->NumberOfProcesses << "." << std::setfill('0')
+               << std::setw(numDigits) << this->MyRank;
+    this->fid = ex_create(myFileName.str().c_str(), EX_CLOBBER,
+                          &compWordSize, &IOWordSize);
     if (fid <= 0)
     {
       vtkErrorMacro (
         << "vtkExodusIIWriter: CreateNewExodusFile can't create "
-        << myFileName);
+        << myFileName.str());
     }
-    delete [] myFileName;
   }
 
   // FileTimeOffset makes the time in the file relative