vtkOStreamWrapper: Support std::string

This will allow std::string to be used with vtkSet/Get macros.

See discussion thread

 VTK coding conventions clarification
 http://www.vtk.org/pipermail/vtk-developers/2014-March/014867.html



It is not possible to portably forward-declare std::string or the
std::basic_string<> template, but we do not want to include <string>.
Instead, use a template that happens to match std::basic_string<> and
forwards to a private implementation (where <string> and <iostream>
are available) by casting through an internal concrete type.  Use
std::char_traits<> and std::allocator<> declarations that we know
vtkSystemIncludes.h brought in before including the
vtkOStreamWrapper.h header.

Add a new "TestOStreamWrapper" test case to cover use of the
vtkOStreamWrapper with std::string in a translation unit that acts
like wrapper-generated sources (define VTK_STREAMS_FWD_ONLY) where
no <iostream> is included.

Suggested-by: David C. Lonie <david.lonie@kitware.com>
Change-Id: I5bf4803b0e4b1e7c899b061fdbd6f66f08cbc7d6

Common/Core/Testing/Cxx/CMakeLists.txt

@@ -37,6 +37,7 @@ vtk_add_test_cxx(NO_DATA NO_VALID NO_OUTPUT
   TestObjectFactory.cxx
   TestObservers.cxx
   TestObserversPerformance.cxx
+  TestOStreamWrapper.cxx
   TestSMP.cxx
   TestSmartPointer.cxx
   TestSortDataArray.cxx

Common/Core/Testing/Cxx/TestOStreamWrapper.cxx

+/*=========================================================================
+
+  Program:   Visualization Toolkit
+  Module:    TestOStreamWrapper.cxx
+
+  Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
+  All rights reserved.
+  See Copyright.txt or http://www.kitware.com/Copyright.htm for details.
+
+     This software is distributed WITHOUT ANY WARRANTY; without even
+     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+     PURPOSE.  See the above copyright notice for more information.
+
+=========================================================================*/
+#define VTK_STREAMS_FWD_ONLY // like wrapper-generated sources
+#include "vtkSystemIncludes.h"
+
+#include <stdio.h> // test covers NOT including <iostream>
+#include <string>
+
+int TestOStreamWrapper(int, char *[])
+{
+  int failed = 0;
+  std::string const expect = "hello, world: 1";
+  std::string actual;
+  std::string s = "hello, world";
+  vtkOStrStreamWrapper vtkmsg;
+  vtkmsg << s << ": " << 1;
+  actual = vtkmsg.str();
+  vtkmsg.rdbuf()->freeze(0);
+  if(actual != expect)
+    {
+    failed = 1;
+    fprintf(stderr, "Expected '%s' but got '%s'\n",
+            expect.c_str(), actual.c_str());
+    }
+  return failed;
+}

Common/Core/vtkOStreamWrapper.cxx

@@ -21,6 +21,8 @@
 #include "vtkObjectBase.h"
 #include "vtkSmartPointerBase.h"
 
+#include <string>
+
 #define VTKOSTREAM_OPERATOR(type) \
   vtkOStreamWrapper& vtkOStreamWrapper::operator << (type a) \
     { this->ostr << a; return *this; }
@@ -86,6 +88,13 @@ VTKOSTREAM_OPERATOR_FUNC(float* (*a)(void*));
 VTKOSTREAM_OPERATOR_FUNC(const char* (*a)(void*));
 VTKOSTREAM_OPERATOR_FUNC(void (*a)(void*, int*));
 
+//----------------------------------------------------------------------------
+vtkOStreamWrapper& vtkOStreamWrapper::operator << (std_string const& s)
+{
+  this->ostr << reinterpret_cast<std::string const&>(s);
+  return *this;
+}
+
 //----------------------------------------------------------------------------
 #if defined(__IBMCPP__)
 vtkOStreamWrapper& vtkOStreamWrapper::WriteInternal(const char* a)

Common/Core/vtkOStreamWrapper.h

@@ -43,6 +43,7 @@ class vtkStdString;
 
 class VTKCOMMONCORE_EXPORT vtkOStreamWrapper
 {
+  class std_string;
 public:
   // Description:
   // Construct class to reference a real ostream.  All methods and
@@ -106,6 +107,14 @@ public:
   vtkOStreamWrapper& operator << (const char* (*)(void*));
   vtkOStreamWrapper& operator << (void (*)(void*, int*));
 
+  // Accept std::string without a declaration.
+  template <template <typename, typename, typename> class S>
+  vtkOStreamWrapper& operator << (const
+    S< char, std::char_traits<char>, std::allocator<char> >& s)
+    {
+    return *this << reinterpret_cast<std_string const&>(s);
+    }
+
   // Description:
   // Forward the write method to the real stream.
   vtkOStreamWrapper& write(const char*, unsigned long);
@@ -137,6 +146,7 @@ protected:
   ostream& ostr;
 private:
   vtkOStreamWrapper& operator=(const vtkOStreamWrapper& r); // Not Implemented.
+  vtkOStreamWrapper& operator << (std_string const&);
 };
 
 #endif