ENH: provide formatting version of Foam::name() (issue #253)

- there are some cases in which the C-style sprintf is much more
  convenient, albeit problematic for buffer overwrites.

  Provide a formatting version of Foam::name() for language
  primitives that is buffer-safe.

  Returns a Foam::word, so that further output will be unquoted, but
  without any checking that the characters are indeed entirely valid
  word characters.

  Example use,
      i = 1234;
      s = Foam::name("%08d", i);
      produces '00001234'

  Alternative using string streams:

      std::ostringstream buf;
      buf.fill('0');
      buf << setw(8) << i;
      s = buf.str();

  Note that the format specification can also be slightly more complex:

     Foam::name("output%08d.vtk", i);
     Foam::name("timing=%.2fs", time);

It remains the caller's responsibility to ensure that the format mask
is valid.

src/OpenFOAM/primitives/strings/stringOps/stringOpsTemplates.C

@@ -0,0 +1,69 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2016 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include <cstdio>
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+// NOTE: with C++11 could consider variadic templates for a more general
+// sprintf implementation
+
+template<class PrimitiveType>
+Foam::word Foam::stringOps::name
+(
+    const char* fmt,
+    const PrimitiveType& val
+)
+{
+    // same concept as GNU/BSD asprintf()
+    // use snprintf with zero to determine the number of characters required
+
+    int n = ::snprintf(0, 0, fmt, val);
+    if (n > 0)
+    {
+        char buf[n+1];
+        ::snprintf(buf, n+1, fmt, val);
+        buf[n] = 0;
+
+        // no stripping desired
+        return word(buf, false);
+    }
+
+    return word::null;
+}
+
+
+template<class PrimitiveType>
+Foam::word Foam::stringOps::name
+(
+    const std::string& fmt,
+    const PrimitiveType& val
+)
+{
+    return stringOps::name(fmt.c_str(), val);
+}
+
+
+// ************************************************************************* //