Fix deallocate for working on old compiers

CMakeLists.txt

@@ -101,6 +101,12 @@ set(CMAKE_LIBRARY_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/lib" CACHE PATH "Library
 set(CMAKE_PDB_OUTPUT_DIRECTORY     "${CMAKE_BINARY_DIR}/bin" CACHE PATH "PDB (MSVC debug symbol)output dir.")
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/bin" CACHE PATH "Executable/dll output dir.")
 
+include(CheckFunctionExists)
+check_function_exists(memset_s HAVE_MEMSET_S)
+if(HAVE_MEMSET_S)
+    add_definitions("-DHAVE_MEMSET_S=1")
+endif()
+
 set(JSONCPP_USE_SECURE_MEMORY "0" CACHE STRING "-D...=1 to use memory-wiping allocator for STL")
 
 configure_file("${PROJECT_SOURCE_DIR}/version.in"

include/json/allocator.h

@@ -8,6 +8,7 @@
 
 #include <cstring>
 #include <memory>
+#include <algorithm>
 
 #pragma pack(push)
 #pragma pack()
@@ -38,8 +39,14 @@ template <typename T> class SecureAllocator {
    * The memory block is filled with zeroes before being released.
    */
   void deallocate(pointer p, size_type n) {
-    // memset_s is used because memset may be optimized away by the compiler
+  #if defined(HAVE_MEMSET_S)
     memset_s(p, n * sizeof(T), 0, n * sizeof(T));
+  #elif defined(_WIN32)
+    RtlSecureZeroMemory(p, n * sizeof(T));
+  #else
+    std::fill_n(reinterpret_cast<volatile unsigned char*>(p), n, 0);
+  #endif
+
     // free using "global operator delete"
     ::operator delete(p);
   }