Change ostringstream to simple string

dune/istl/matrixmarket.hh

@@ -1136,11 +1136,10 @@ namespace Dune
                          std::string filename,
                          int prec=default_precision)
   {
-    std::ostringstream rfilename;
-    rfilename << filename << ".mm";
-    std::ofstream file(rfilename.str().c_str());
+    std::string rfilename = filename + ".mm";
+    std::ofstream file(rfilename.c_str());
     if(!file)
-      DUNE_THROW(IOError, "Could not open file for storage: " << rfilename.str().c_str());
+      DUNE_THROW(IOError, "Could not open file for storage: " << rfilename.c_str());
     file.setf(std::ios::scientific,std::ios::floatfield);
     if(prec>0)
       file.precision(prec);
@@ -1312,12 +1311,11 @@ namespace Dune
   void loadMatrixMarket(M& matrix,
                         const std::string& filename)
   {
-    std::ostringstream rfilename;
-    rfilename << filename << ".mm";
+    std::string rfilename = filename + ".mm";
     std::ifstream file;
-    file.open(rfilename.str().c_str(), std::ios::in);
+    file.open(rfilename.c_str(), std::ios::in);
     if(!file)
-      DUNE_THROW(IOError, "Could not open file: " << rfilename.str().c_str());
+      DUNE_THROW(IOError, "Could not open file: " << rfilename.c_str());
     readMatrixMarket(matrix,file);
     file.close();
   }