ENH: Pointer-to-function to pointer-to-data casts are not even allowed in strict C. Re-implemented this conversion in pure C++ using a casting trick with an extra level of indirection.

Source/CMakeLists.txt

@@ -10,7 +10,6 @@ cmSourceFile.cxx
 cmSystemTools.cxx
 cmDirectory.cxx
 cmDynamicLoader.cxx
-cmDynamicLoaderC.c
 cmCommands.cxx
 cmTarget.cxx
 cmCustomCommand.cxx

Source/cmDynamicLoader.cxx

@@ -16,20 +16,7 @@
 =========================================================================*/
 #include "cmDynamicLoader.h"
 
-extern "C"
-{
-cmDynamicLoaderFunction cmDynamicLoaderGetSymbolAddress(cmLibHandle,
-                                                        const char*);
-}
-
-// Dispatch to C implementation.
-cmDynamicLoaderFunction cmDynamicLoader::GetSymbolAddress(cmLibHandle lib,
-                                                          const char* sym)
-{
-  return cmDynamicLoaderGetSymbolAddress(lib, sym);
-}
-
-// This file is actually 4 different implementations.
+// This file is actually several different implementations.
 // 1. HP machines which uses shl_load
 // 2. Apple OSX which uses NSLinkModule
 // 3. Windows which uses LoadLibrary
@@ -53,6 +40,19 @@ int cmDynamicLoader::CloseLibrary(cmLibHandle lib)
   return 0;
 }
 
+cmDynamicLoaderFunction
+cmDynamicLoader::GetSymbolAddress(cmLibHandle lib, const char* sym)
+{ 
+  void* addr;
+  int status;
+  
+  status = shl_findsym (&lib, sym, TYPE_PROCEDURE, &addr);
+  void* result = (status < 0) ? (void*)0 : addr;
+  
+  // Hack to cast pointer-to-data to pointer-to-function.
+  return *reinterpret_cast<cmDynamicLoaderFunction*>(&result);
+}
+
 const char* cmDynamicLoader::LibPrefix()
 { 
   return "lib";
@@ -92,6 +92,22 @@ int cmDynamicLoader::CloseLibrary(cmLibHandle lib)
   return 0;
 }
 
+cmDynamicLoaderFunction
+cmDynamicLoader::GetSymbolAddress(cmLibHandle lib, const char* sym)
+{
+  void *result=0;
+  if(NSIsSymbolNameDefined(sym))
+    {
+    NSSymbol symbol= NSLookupAndBindSymbol(sym);
+    if(symbol)
+      {
+      result = NSAddressOfSymbol(symbol);
+      }
+    }
+  // Hack to cast pointer-to-data to pointer-to-function.
+  return *reinterpret_cast<cmDynamicLoaderFunction*>(&result);
+}
+
 const char* cmDynamicLoader::LibPrefix()
 {
   return "";
@@ -136,6 +152,23 @@ int cmDynamicLoader::CloseLibrary(cmLibHandle lib)
   return (int)FreeLibrary(lib);
 }
 
+cmDynamicLoaderFunction
+cmDynamicLoader::GetSymbolAddress(cmLibHandle lib, const char* sym)
+{ 
+  void* result = 0;
+#ifdef UNICODE
+        wchar_t *wsym = new wchar_t [mbstowcs(NULL, sym, 32000)];
+        mbstowcs(wsym, sym, 32000);
+        void *ret = GetProcAddress(lib, wsym);
+        delete [] wsym;
+        result = ret;
+#else
+  result = GetProcAddress(lib, sym);
+#endif
+  // Hack to cast pointer-to-data to pointer-to-function.
+  return *reinterpret_cast<cmDynamicLoaderFunction*>(&result);
+}
+
 const char* cmDynamicLoader::LibPrefix()
 { 
   return "";
@@ -188,6 +221,15 @@ int cmDynamicLoader::CloseLibrary(cmLibHandle lib)
   return (int)dlclose(lib);
 }
 
+cmDynamicLoaderFunction
+cmDynamicLoader::GetSymbolAddress(cmLibHandle lib, const char* sym)
+{ 
+  void* result = dlsym(lib, sym);
+  
+  // Hack to cast pointer-to-data to pointer-to-function.
+  return *reinterpret_cast<cmDynamicLoaderFunction*>(&result);
+}
+
 const char* cmDynamicLoader::LibPrefix()
 { 
   return "lib";

Source/cmDynamicLoader.h

@@ -37,16 +37,8 @@
   typedef void* cmLibHandle;
 #endif
 
-// C++ Does not allow casts from pointer-to-data types to
-// pointer-to-function types.  However, the return type from each
-// platform's symbol lookup implementation is void*.  We need to hide
-// the cast from void* to a pointer-to-function type in C code.  The
-// implementation of cmDynamicLoader::GetSymbolAddress simply calls a
-// C-based implementation in cmDynamicLoaderC.c.  This
-// cmDynamicLoaderFunction type is the return type of
-// cmDynamicLoader::GetSymbolAddress and can be cast to any other
-// pointer-to-function type safely in C++.
-extern "C" { typedef void (*cmDynamicLoaderFunction)(); }
+// Return type from cmDynamicLoader::GetSymbolAddress.
+typedef void (*cmDynamicLoaderFunction)();
 
 class cmDynamicLoader
 {

Source/cmDynamicLoaderC.c

@@ -1,118 +0,0 @@
-/*=========================================================================
-
-  Program:   Insight Segmentation & Registration Toolkit
-  Module:    $RCSfile$
-  Language:  C++
-  Date:      $Date$
-  Version:   $Revision$
-
-  Copyright (c) 2002 Insight Consortium. All rights reserved.
-  See ITKCopyright.txt or http://www.itk.org/HTML/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 notices for more information.
-
-=========================================================================*/
-
-/*
- * This file is actually 4 different implementations.
- * 1. HP machines which uses shl_load
- * 2. Apple OSX which uses NSLinkModule
- * 3. Windows which uses LoadLibrary
- * 4. Most unix systems which use dlopen (default )
- * Each part of the ifdef contains a complete implementation for
- * the static methods of cmDynamicLoader.  
- */
-
-/* Ugly stuff for library handles.  They are different on several
-   different OS's */
-#if defined(__hpux)
-# include <dl.h>
-  typedef shl_t cmLibHandle;
-#elif defined(_WIN32)
-  #include <windows.h>
-  typedef HMODULE cmLibHandle;
-#else
-  typedef void* cmLibHandle;
-#endif
-
-typedef void (*cmDynamicLoaderFunction)();
-
-/* --------------------------------------------------------------- */
-/* 1. Implementation for HPUX  machines */
-#ifdef __hpux
-#define CMDYNAMICLOADER_DEFINED 1
-#include <dl.h>
-
-cmDynamicLoaderFunction cmDynamicLoaderGetSymbolAddress(cmLibHandle lib,
-                                                        const char* sym)
-{ 
-  void* addr;
-  int status;
-  
-  status = shl_findsym (&lib, sym, TYPE_PROCEDURE, &addr);
-  return (cmDynamicLoaderFunction)((status < 0) ? (void*)0 : addr);
-}
-#endif
-
-
-/* --------------------------------------------------------------- */
-/* 2. Implementation for Darwin (including OSX) Machines */
-
-#ifdef __APPLE__
-#define CMDYNAMICLOADER_DEFINED
-#include <mach-o/dyld.h>
-
-cmDynamicLoaderFunction cmDynamicLoaderGetSymbolAddress(cmLibHandle lib,
-                                                        const char* sym)
-{ 
-  void *result=0;
-  if(NSIsSymbolNameDefined(sym))
-    {
-    NSSymbol symbol= NSLookupAndBindSymbol(sym);
-    if(symbol)
-      {
-      result = NSAddressOfSymbol(symbol);
-      }
-    }
-  return (cmDynamicLoaderFunction)result;
-}
-#endif
-
-
-/* --------------------------------------------------------------- */
-/* 3. Implementation for Windows win32 code */
-#ifdef _WIN32
-#include <windows.h>
-#define CMDYNAMICLOADER_DEFINED 1
-
-cmDynamicLoaderFunction cmDynamicLoaderGetSymbolAddress(cmLibHandle lib,
-                                                        const char* sym)
-{ 
-#ifdef UNICODE
-        wchar_t *wsym = new wchar_t [mbstowcs(NULL, sym, 32000)];
-        mbstowcs(wsym, sym, 32000);
-        void *ret = GetProcAddress(lib, wsym);
-        delete [] wsym;
-        return (cmDynamicLoaderFunction)ret;
-#else
-  return (cmDynamicLoaderFunction)GetProcAddress(lib, sym);
-#endif
-}
-#endif
-
-/* --------------------------------------------------------------- */
-/* 4. Implementation for default UNIX machines.
-   if nothing has been defined then use this  */
-#ifndef CMDYNAMICLOADER_DEFINED
-#define CMDYNAMICLOADER_DEFINED
-/* Setup for most unix machines */
-#include <dlfcn.h>
-
-cmDynamicLoaderFunction cmDynamicLoaderGetSymbolAddress(cmLibHandle lib,
-                                                        const char* sym)
-{ 
-  return (cmDynamicLoaderFunction)dlsym(lib, sym);
-}
-#endif