ENH: support OFstream "/dev/null" equivalent directly

- uses ocountstream for the output, which swallows all output.
  Improves portability

ENH: improved efficiency in countstreambuf

- xsputn() instead of overflow
- more consistent seek* methods

src/OpenFOAM/db/IOstreams/Fstreams/OFstream.C

@@ -39,6 +39,21 @@ namespace Foam
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
+Foam::OFstream::OFstream
+(
+    std::nullptr_t
+)
+:
+    Foam::ofstreamPointer(nullptr),
+    OSstream(*(ofstreamPointer::get()), "/dev/null")
+{
+    setState(ofstreamPointer::get()->rdstate());
+    setOpened();
+
+    lineNumber_ = 1;
+}
+
+
 Foam::OFstream::OFstream
 (
     const fileName& pathname,

src/OpenFOAM/db/IOstreams/Fstreams/OFstream.H

@@ -64,6 +64,10 @@ public:
 
     // Constructors
 
+        //- Construct a null output file stream.
+        //  Behaves like \c /dev/null and is named accordingly
+        explicit OFstream(std::nullptr_t);
+
         //- Construct from pathname
         explicit OFstream
         (

src/OpenFOAM/db/IOstreams/Fstreams/fstreamPointer.H

@@ -82,7 +82,7 @@ protected:
     // Protected Member Functions
 
         //- Special 'rewind' method for compressed stream
-        void reopen_gz(const fileName& pathname_gz);
+        void reopen_gz(const std::string& pathname_gz);
 
 public:
 
@@ -164,7 +164,7 @@ class ofstreamPointer
 {
     // Private Data
 
-        //- The stream pointer (ofstream or ogzstream)
+        //- The stream pointer (ofstream | ogzstream | ocountstream)
         std::unique_ptr<std::ostream> ptr_;
 
 public:
@@ -192,6 +192,9 @@ public:
 
     // Constructors
 
+        //- Construct as null output stream using Foam::ocountstream
+        explicit ofstreamPointer(std::nullptr_t);
+
         //- Construct from pathname, with specified append option
         ofstreamPointer(const fileName& pathname, const bool append)
         :

src/OpenFOAM/db/IOstreams/Fstreams/fstreamPointers.C

@@ -27,6 +27,7 @@ License
 \*---------------------------------------------------------------------------*/
 
 #include "fstreamPointer.H"
+#include "OCountStream.H"
 #include "OSspecific.H"
 
 // HAVE_LIBZ defined externally
@@ -131,6 +132,12 @@ Foam::ifstreamPointer::ifstreamPointer
 }
 
 
+Foam::ofstreamPointer::ofstreamPointer(std::nullptr_t)
+:
+    ptr_(new Foam::ocountstream)
+{}
+
+
 Foam::ofstreamPointer::ofstreamPointer
 (
     const fileName& pathname,
@@ -184,7 +191,7 @@ Foam::ofstreamPointer::ofstreamPointer
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-void Foam::ifstreamPointer::reopen_gz(const fileName& pathname_gz)
+void Foam::ifstreamPointer::reopen_gz(const std::string& pathname_gz)
 {
     #ifdef HAVE_LIBZ
     igzstream* gz = dynamic_cast<igzstream*>(ptr_.get());

src/OpenFOAM/db/IOstreams/IOstreams.C

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011 OpenFOAM Foundation
-    Copyright (C) 2018 OpenCFD Ltd.
+    Copyright (C) 2018-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -49,7 +49,7 @@ unsigned int Foam::IOstream::precision_
 Foam::ISstream Foam::Sin(std::cin, "Sin");
 Foam::OSstream Foam::Sout(std::cout, "Sout");
 Foam::OSstream Foam::Serr(std::cerr, "Serr");
-Foam::OFstream Foam::Snull("/dev/null");
+Foam::OFstream Foam::Snull(nullptr);  // A "/dev/null" equivalent
 
 Foam::prefixOSstream Foam::Pout(std::cout, "Pout");
 Foam::prefixOSstream Foam::Perr(std::cerr, "Perr");

src/OpenFOAM/db/IOstreams/IOstreams.H

@@ -6,6 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011 OpenFOAM Foundation
+    Copyright (C) 2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -49,19 +50,19 @@ Description
 
 namespace Foam
 {
-    //- An Istream wrapper for std::cin
+    //- ISstream wrapped stdin (std::cin)
     extern ISstream Sin;
 
-    //- An Ostream wrapper for std::cout
+    //- OSstream wrapped stdout (std::cout)
     extern OSstream Sout;
 
-    //- An Ostream wrapper for std::cerr
+    //- OSstream wrapped stderr (std::cerr)
     extern OSstream Serr;
 
-    //- An Ostream wrapper for parallel output to std::cout
+    //- OSstream wrapped stdout (std::cout) with parallel prefix
     extern prefixOSstream Pout;
 
-    //- An Ostream wrapper for parallel output to std::cerr
+    //- OSstream wrapped stderr (std::cerr) with parallel prefix
     extern prefixOSstream Perr;
 }
 

src/OpenFOAM/db/IOstreams/memory/OCountStream.H

@@ -56,6 +56,48 @@ class countstreambuf
 
 protected:
 
+    //- Set position pointer to relative position
+    virtual std::streampos seekoff
+    (
+        std::streamoff off,
+        std::ios_base::seekdir way,
+        std::ios_base::openmode which = std::ios_base::in|std::ios_base::out
+    )
+    {
+        if (which & std::ios_base::out)
+        {
+            if (way == std::ios_base::beg)
+            {
+                size_ = off;
+            }
+            else if (way == std::ios_base::cur)
+            {
+                size_ += off;
+            }
+            else if (way == std::ios_base::end)
+            {
+                // not really possible
+            }
+
+            return size_; // tellp()
+        }
+
+        return -1;
+    }
+
+
+    //- Set position pointer to absolute position
+    //  For the counter, adjust the count accordingly.
+    virtual std::streampos seekpos
+    (
+        std::streampos pos,
+        std::ios_base::openmode which = std::ios_base::in|std::ios_base::out
+    )
+    {
+        return seekoff(pos, std::ios_base::beg, which);
+    }
+
+
     //- Handle output counting via overflow
     virtual int overflow(int c = EOF)
     {
@@ -66,35 +108,31 @@ protected:
         return c;
     }
 
-    //- Set position pointer to absolute position
-    //  For the counter, any positioning is ignored and it always acts like
-    //  seekpos(0), which resets the count.
-    virtual std::streampos seekpos
-    (
-        std::streampos,
-        std::ios_base::openmode which = std::ios_base::in|std::ios_base::out
-    )
+
+    //- Put sequence of characters
+    virtual std::streamsize xsputn(const char* s, std::streamsize n)
     {
-        size_ = 0;
-        return 0;
+        size_ += n;
+        return n;
     }
 
+
 public:
 
     //- Default construct, or with precount size
-    countstreambuf(std::streamsize precount=0)
+    explicit countstreambuf(std::streamsize precount=0)
     :
         size_(precount)
     {}
 
-    //- \return The number of bytes counted
-    std::streamsize size() const
+    //- \return The buffer put position == number of bytes counted.
+    std::streamsize tellp() const
     {
         return size_;
     }
 
     //- Some information about the number of bytes counted
-    inline void printBufInfo(Ostream& os) const
+    void printBufInfo(Ostream& os) const
     {
         os << "count=" << size_;
     }
@@ -124,8 +162,14 @@ public:
     {}
 
 
+    //- \return The buffer put position == number of bytes counted.
+    using countstreambuf::tellp;
+
     //- \return The number of bytes counted
-    using countstreambuf::size;
+    std::streamsize size() const
+    {
+        return countstreambuf::tellp();
+    }
 
     //- Rewind the stream, reset the count
     void rewind()
@@ -183,7 +227,7 @@ public:
         //- The number of bytes counted
         std::streamsize size() const
         {
-            return buf_.size();
+            return buf_.tellp();
         }
 
         //- Rewind the stream, reset the count