BUG: Fix locale-dependent parsing in NRRD reader causing metadata corruption

Modules/Core/Common/CMake/itkCheckHasConfigthreadlocale.cxx

@@ -0,0 +1,31 @@
+/*=========================================================================
+ *
+ *  Copyright NumFOCUS
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         https://www.apache.org/licenses/LICENSE-2.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *=========================================================================*/
+
+// Check if _configthreadlocale is available (Windows thread-local locale)
+#include <locale.h>
+
+int
+main()
+{
+  int prev = _configthreadlocale(_ENABLE_PER_THREAD_LOCALE);
+  if (prev != -1)
+  {
+    _configthreadlocale(prev);
+  }
+  return 0;
+}

Modules/Core/Common/CMake/itkCheckHasNewlocale.cxx

@@ -0,0 +1,37 @@
+/*=========================================================================
+ *
+ *  Copyright NumFOCUS
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         https://www.apache.org/licenses/LICENSE-2.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *=========================================================================*/
+
+// Check if newlocale and uselocale are available (POSIX thread-local locale)
+#include <locale.h>
+
+#if defined(__APPLE__)
+#  include <xlocale.h>
+#endif
+
+int
+main()
+{
+  locale_t loc = newlocale(LC_NUMERIC_MASK, "C", nullptr);
+  if (loc)
+  {
+    locale_t prev = uselocale(loc);
+    uselocale(prev);
+    freelocale(loc);
+  }
+  return 0;
+}

Modules/Core/Common/CMakeLists.txt

@@ -157,6 +157,29 @@ try_compile(
   ${CMAKE_CURRENT_SOURCE_DIR}/CMake/itkCheckHasSchedGetAffinity.cxx
 )
 
+# Check for thread-local locale functions for NumericLocale
+try_compile(
+  ITK_HAS_NEWLOCALE
+  ${ITK_BINARY_DIR}
+  ${CMAKE_CURRENT_SOURCE_DIR}/CMake/itkCheckHasNewlocale.cxx
+)
+
+try_compile(
+  ITK_HAS_CONFIGTHREADLOCALE
+  ${ITK_BINARY_DIR}
+  ${CMAKE_CURRENT_SOURCE_DIR}/CMake/itkCheckHasConfigthreadlocale.cxx
+)
+
+# Warn if no thread-safe locale method is available
+if(NOT ITK_HAS_NEWLOCALE AND NOT ITK_HAS_CONFIGTHREADLOCALE)
+  message(
+    WARNING
+    "Neither POSIX newlocale/uselocale nor Windows _configthreadlocale detected. "
+    "Thread-safe numeric locale handling is not available. "
+    "Locale must be managed at the application level if needed."
+  )
+endif()
+
 #-----------------------------------------------------------------------------
 # Make default visibility as an option for generated export header
 

Modules/Core/Common/include/itkNumericLocale.h

@@ -0,0 +1,84 @@
+/*=========================================================================
+ *
+ *  Copyright NumFOCUS
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         https://www.apache.org/licenses/LICENSE-2.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *=========================================================================*/
+#ifndef itkNumericLocale_h
+#define itkNumericLocale_h
+
+#include "itkMacro.h"
+#include "ITKCommonExport.h"
+
+#include <memory>
+
+namespace itk
+{
+
+/** \class NumericLocale
+ * \brief RAII class for thread-safe temporary setting of LC_NUMERIC locale to "C".
+ *
+ * This class provides a thread-safe mechanism to temporarily set the LC_NUMERIC
+ * locale to "C" for locale-independent parsing and formatting of floating-point
+ * numbers. The original locale is automatically restored when the object goes
+ * out of scope.
+ *
+ * This is particularly useful when parsing file formats that use dot as decimal
+ * separator (like NRRD, VTK, etc.) regardless of the system locale setting.
+ *
+ * Thread safety:
+ * - On POSIX systems (when newlocale/uselocale are available): Uses thread-local locale
+ * - On Windows (when _configthreadlocale is available): Uses thread-specific locale
+ * - Fallback (when neither is available): Issues a warning if locale differs from "C",
+ *   but does not change the locale. Applications must manage locale externally.
+ *
+ * Example usage:
+ * \code
+ * {
+ *   NumericLocale cLocale;
+ *   // Parse file with dot decimal separator
+ *   double value = std::strtod("3.14159", nullptr);
+ *   // Locale automatically restored here
+ * }
+ * \endcode
+ *
+ * \ingroup ITKCommon
+ */
+class ITKCommon_EXPORT NumericLocale
+{
+public:
+  /** Constructor: Saves current LC_NUMERIC locale and sets it to "C" */
+  NumericLocale();
+
+  /** Destructor: Restores the original LC_NUMERIC locale */
+  ~NumericLocale();
+
+  // Delete copy and move operations
+  NumericLocale(const NumericLocale &) = delete;
+  NumericLocale &
+  operator=(const NumericLocale &) = delete;
+  NumericLocale(NumericLocale &&) = delete;
+  NumericLocale &
+  operator=(NumericLocale &&) = delete;
+
+private:
+  // Forward declaration of implementation structure
+  struct Impl;
+  // Pointer to implementation (pImpl idiom)
+  std::unique_ptr<Impl> m_Impl;
+};
+
+} // end namespace itk
+
+#endif // itkNumericLocale_h

Modules/Core/Common/src/CMakeLists.txt

@@ -66,6 +66,7 @@ set(
   itkLogger.cxx
   itkLogOutput.cxx
   itkLoggerOutput.cxx
+  itkNumericLocale.cxx
   itkProgressAccumulator.cxx
   itkTotalProgressReporter.cxx
   itkNumericTraits.cxx

Modules/Core/Common/src/itkConfigurePrivate.h.in

@@ -33,4 +33,9 @@
 // defined if fenv_t struct as __cw member
 #cmakedefine ITK_HAS_STRUCT_FENV_T_CW
 
+// defined if newlocale/uselocale are available (POSIX thread-local locale)
+#cmakedefine ITK_HAS_NEWLOCALE
+// defined if _configthreadlocale is available (Windows thread-local locale)
+#cmakedefine ITK_HAS_CONFIGTHREADLOCALE
+
 #endif //itkConfigurePrivate_h

Modules/Core/Common/src/itkNumericLocale.cxx

@@ -0,0 +1,150 @@
+/*=========================================================================
+ *
+ *  Copyright NumFOCUS
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         https://www.apache.org/licenses/LICENSE-2.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *=========================================================================*/
+
+#include "itkNumericLocale.h"
+#include "itkConfigurePrivate.h"
+
+#include <locale.h>
+#include <cstring>
+#include <cstdlib>
+
+// Include platform-specific headers based on detected features
+#ifdef ITK_HAS_NEWLOCALE
+#  if defined(__APPLE__)
+#    include <xlocale.h>
+#  endif
+#endif
+
+namespace itk
+{
+
+// Implementation structure definition
+struct NumericLocale::Impl
+{
+#ifdef ITK_HAS_CONFIGTHREADLOCALE
+  // Windows: thread-specific locale
+  int    m_PreviousThreadLocaleSetting{ -1 };
+  char * m_SavedLocale{ nullptr };
+#elif defined(ITK_HAS_NEWLOCALE)
+  // POSIX: thread-local locale
+  locale_t m_PreviousLocale{ nullptr };
+  locale_t m_CLocale{ nullptr };
+#else
+  // Fallback: no locale change, only check and warn
+  bool m_WarningIssued{ false };
+#endif
+};
+
+#ifdef ITK_HAS_CONFIGTHREADLOCALE
+
+// Windows implementation using thread-specific locale
+NumericLocale::NumericLocale()
+  : m_Impl(new Impl())
+{
+  // Enable thread-specific locale for this thread
+  m_Impl->m_PreviousThreadLocaleSetting = _configthreadlocale(_ENABLE_PER_THREAD_LOCALE);
+
+  // Save current LC_NUMERIC locale
+  const char * currentLocale = setlocale(LC_NUMERIC, nullptr);
+  if (currentLocale)
+  {
+    m_Impl->m_SavedLocale = _strdup(currentLocale);
+    // If _strdup fails (returns nullptr), m_SavedLocale remains nullptr
+    // and the locale will not be restored in the destructor
+  }
+
+  // Set to C locale for parsing
+  setlocale(LC_NUMERIC, "C");
+}
+
+NumericLocale::~NumericLocale()
+{
+  // Restore original locale
+  if (m_Impl->m_SavedLocale)
+  {
+    setlocale(LC_NUMERIC, m_Impl->m_SavedLocale);
+    free(m_Impl->m_SavedLocale);
+  }
+
+  // Restore previous thread-specific locale setting
+  if (m_Impl->m_PreviousThreadLocaleSetting != -1)
+  {
+    _configthreadlocale(m_Impl->m_PreviousThreadLocaleSetting);
+  }
+}
+
+#elif defined(ITK_HAS_NEWLOCALE)
+
+// POSIX implementation using thread-local locale (uselocale/newlocale)
+NumericLocale::NumericLocale()
+  : m_Impl(new Impl())
+{
+  // Create a new C locale
+  // If newlocale fails (returns nullptr), m_CLocale remains nullptr
+  // and the locale will not be changed - this is a safe fallback
+  m_Impl->m_CLocale = newlocale(LC_NUMERIC_MASK, "C", nullptr);
+
+  if (m_Impl->m_CLocale)
+  {
+    // Set the C locale for this thread and save the previous locale
+    // uselocale returns the previous locale, which may be LC_GLOBAL_LOCALE
+    m_Impl->m_PreviousLocale = uselocale(m_Impl->m_CLocale);
+  }
+}
+
+NumericLocale::~NumericLocale()
+{
+  // If we created and installed a C locale for this thread,
+  // restore the previous locale and free the C locale.
+  // Always restore if m_CLocale is set, as m_PreviousLocale may be
+  // LC_GLOBAL_LOCALE which is a valid non-null value.
+  if (m_Impl->m_CLocale)
+  {
+    uselocale(m_Impl->m_PreviousLocale);
+    freelocale(m_Impl->m_CLocale);
+  }
+}
+
+#else
+
+// Fallback implementation - only check locale and issue warning if not "C"
+// Do not modify the locale, application must manage it externally
+NumericLocale::NumericLocale()
+  : m_Impl(new Impl())
+{
+  // Check if current locale is compatible with expected "C" locale
+  const char * currentLocale = setlocale(LC_NUMERIC, nullptr);
+  if (currentLocale && std::strcmp(currentLocale, "C") != 0)
+  {
+    // Issue warning only once per instance
+    itkWarningMacro("LC_NUMERIC locale is '" << currentLocale << "' (not 'C'). "
+                                             << "Thread-safe locale functions not available. "
+                                             << "Locale-dependent number parsing may cause issues. "
+                                             << "Please manage locale at application level.");
+    m_Impl->m_WarningIssued = true;
+  }
+}
+
+NumericLocale::~NumericLocale()
+{
+  // No action needed in fallback - we don't change the locale
+}
+
+#endif
+
+} // end namespace itk

Modules/Core/Common/test/CMakeLists.txt

@@ -1887,6 +1887,7 @@ set(
   itkMersenneTwisterRandomVariateGeneratorGTest.cxx
   itkNeighborhoodAllocatorGTest.cxx
   itkNumberToStringGTest.cxx
+  itkNumericLocaleGTest.cxx
   itkObjectFactoryBaseGTest.cxx
   itkOffsetGTest.cxx
   itkOptimizerParametersGTest.cxx