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raidjson/rapidjson/allocators.h

@@ -0,0 +1,692 @@
+// Tencent is pleased to support the open source community by making RapidJSON available.
+// 
+// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip.
+//
+// Licensed under the MIT License (the "License"); you may not use this file except
+// in compliance with the License. You may obtain a copy of the License at
+//
+// http://opensource.org/licenses/MIT
+//
+// 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 RAPIDJSON_ALLOCATORS_H_
+#define RAPIDJSON_ALLOCATORS_H_
+
+#include "rapidjson.h"
+#include "internal/meta.h"
+
+#include <memory>
+
+#if RAPIDJSON_HAS_CXX11
+#include <type_traits>
+#endif
+
+RAPIDJSON_NAMESPACE_BEGIN
+
+///////////////////////////////////////////////////////////////////////////////
+// Allocator
+
+/*! \class rapidjson::Allocator
+    \brief Concept for allocating, resizing and freeing memory block.
+    
+    Note that Malloc() and Realloc() are non-static but Free() is static.
+    
+    So if an allocator need to support Free(), it needs to put its pointer in 
+    the header of memory block.
+
+\code
+concept Allocator {
+    static const bool kNeedFree;    //!< Whether this allocator needs to call Free().
+
+    // Allocate a memory block.
+    // \param size of the memory block in bytes.
+    // \returns pointer to the memory block.
+    void* Malloc(size_t size);
+
+    // Resize a memory block.
+    // \param originalPtr The pointer to current memory block. Null pointer is permitted.
+    // \param originalSize The current size in bytes. (Design issue: since some allocator may not book-keep this, explicitly pass to it can save memory.)
+    // \param newSize the new size in bytes.
+    void* Realloc(void* originalPtr, size_t originalSize, size_t newSize);
+
+    // Free a memory block.
+    // \param pointer to the memory block. Null pointer is permitted.
+    static void Free(void *ptr);
+};
+\endcode
+*/
+
+
+/*! \def RAPIDJSON_ALLOCATOR_DEFAULT_CHUNK_CAPACITY
+    \ingroup RAPIDJSON_CONFIG
+    \brief User-defined kDefaultChunkCapacity definition.
+
+    User can define this as any \c size that is a power of 2.
+*/
+
+#ifndef RAPIDJSON_ALLOCATOR_DEFAULT_CHUNK_CAPACITY
+#define RAPIDJSON_ALLOCATOR_DEFAULT_CHUNK_CAPACITY (64 * 1024)
+#endif
+
+
+///////////////////////////////////////////////////////////////////////////////
+// CrtAllocator
+
+//! C-runtime library allocator.
+/*! This class is just wrapper for standard C library memory routines.
+    \note implements Allocator concept
+*/
+class CrtAllocator {
+public:
+    static const bool kNeedFree = true;
+    void* Malloc(size_t size) { 
+        if (size) //  behavior of malloc(0) is implementation defined.
+            return RAPIDJSON_MALLOC(size);
+        else
+            return NULL; // standardize to returning NULL.
+    }
+    void* Realloc(void* originalPtr, size_t originalSize, size_t newSize) {
+        (void)originalSize;
+        if (newSize == 0) {
+            RAPIDJSON_FREE(originalPtr);
+            return NULL;
+        }
+        return RAPIDJSON_REALLOC(originalPtr, newSize);
+    }
+    static void Free(void *ptr) RAPIDJSON_NOEXCEPT { RAPIDJSON_FREE(ptr); }
+
+    bool operator==(const CrtAllocator&) const RAPIDJSON_NOEXCEPT {
+        return true;
+    }
+    bool operator!=(const CrtAllocator&) const RAPIDJSON_NOEXCEPT {
+        return false;
+    }
+};
+
+///////////////////////////////////////////////////////////////////////////////
+// MemoryPoolAllocator
+
+//! Default memory allocator used by the parser and DOM.
+/*! This allocator allocate memory blocks from pre-allocated memory chunks. 
+
+    It does not free memory blocks. And Realloc() only allocate new memory.
+
+    The memory chunks are allocated by BaseAllocator, which is CrtAllocator by default.
+
+    User may also supply a buffer as the first chunk.
+
+    If the user-buffer is full then additional chunks are allocated by BaseAllocator.
+
+    The user-buffer is not deallocated by this allocator.
+
+    \tparam BaseAllocator the allocator type for allocating memory chunks. Default is CrtAllocator.
+    \note implements Allocator concept
+*/
+template <typename BaseAllocator = CrtAllocator>
+class MemoryPoolAllocator {
+    //! Chunk header for perpending to each chunk.
+    /*! Chunks are stored as a singly linked list.
+    */
+    struct ChunkHeader {
+        size_t capacity;    //!< Capacity of the chunk in bytes (excluding the header itself).
+        size_t size;        //!< Current size of allocated memory in bytes.
+        ChunkHeader *next;  //!< Next chunk in the linked list.
+    };
+
+    struct SharedData {
+        ChunkHeader *chunkHead;  //!< Head of the chunk linked-list. Only the head chunk serves allocation.
+        BaseAllocator* ownBaseAllocator; //!< base allocator created by this object.
+        size_t refcount;
+        bool ownBuffer;
+    };
+
+    static const size_t SIZEOF_SHARED_DATA = RAPIDJSON_ALIGN(sizeof(SharedData));
+    static const size_t SIZEOF_CHUNK_HEADER = RAPIDJSON_ALIGN(sizeof(ChunkHeader));
+
+    static inline ChunkHeader *GetChunkHead(SharedData *shared)
+    {
+        return reinterpret_cast<ChunkHeader*>(reinterpret_cast<uint8_t*>(shared) + SIZEOF_SHARED_DATA);
+    }
+    static inline uint8_t *GetChunkBuffer(SharedData *shared)
+    {
+        return reinterpret_cast<uint8_t*>(shared->chunkHead) + SIZEOF_CHUNK_HEADER;
+    }
+
+    static const size_t kDefaultChunkCapacity = RAPIDJSON_ALLOCATOR_DEFAULT_CHUNK_CAPACITY; //!< Default chunk capacity.
+
+public:
+    static const bool kNeedFree = false;    //!< Tell users that no need to call Free() with this allocator. (concept Allocator)
+    static const bool kRefCounted = true;   //!< Tell users that this allocator is reference counted on copy
+
+    //! Constructor with chunkSize.
+    /*! \param chunkSize The size of memory chunk. The default is kDefaultChunkSize.
+        \param baseAllocator The allocator for allocating memory chunks.
+    */
+    explicit
+    MemoryPoolAllocator(size_t chunkSize = kDefaultChunkCapacity, BaseAllocator* baseAllocator = 0) : 
+        chunk_capacity_(chunkSize),
+        baseAllocator_(baseAllocator ? baseAllocator : RAPIDJSON_NEW(BaseAllocator)()),
+        shared_(static_cast<SharedData*>(baseAllocator_ ? baseAllocator_->Malloc(SIZEOF_SHARED_DATA + SIZEOF_CHUNK_HEADER) : 0))
+    {
+        RAPIDJSON_ASSERT(baseAllocator_ != 0);
+        RAPIDJSON_ASSERT(shared_ != 0);
+        if (baseAllocator) {
+            shared_->ownBaseAllocator = 0;
+        }
+        else {
+            shared_->ownBaseAllocator = baseAllocator_;
+        }
+        shared_->chunkHead = GetChunkHead(shared_);
+        shared_->chunkHead->capacity = 0;
+        shared_->chunkHead->size = 0;
+        shared_->chunkHead->next = 0;
+        shared_->ownBuffer = true;
+        shared_->refcount = 1;
+    }
+
+    //! Constructor with user-supplied buffer.
+    /*! The user buffer will be used firstly. When it is full, memory pool allocates new chunk with chunk size.
+
+        The user buffer will not be deallocated when this allocator is destructed.
+
+        \param buffer User supplied buffer.
+        \param size Size of the buffer in bytes. It must at least larger than sizeof(ChunkHeader).
+        \param chunkSize The size of memory chunk. The default is kDefaultChunkSize.
+        \param baseAllocator The allocator for allocating memory chunks.
+    */
+    MemoryPoolAllocator(void *buffer, size_t size, size_t chunkSize = kDefaultChunkCapacity, BaseAllocator* baseAllocator = 0) :
+        chunk_capacity_(chunkSize),
+        baseAllocator_(baseAllocator),
+        shared_(static_cast<SharedData*>(AlignBuffer(buffer, size)))
+    {
+        RAPIDJSON_ASSERT(size >= SIZEOF_SHARED_DATA + SIZEOF_CHUNK_HEADER);
+        shared_->chunkHead = GetChunkHead(shared_);
+        shared_->chunkHead->capacity = size - SIZEOF_SHARED_DATA - SIZEOF_CHUNK_HEADER;
+        shared_->chunkHead->size = 0;
+        shared_->chunkHead->next = 0;
+        shared_->ownBaseAllocator = 0;
+        shared_->ownBuffer = false;
+        shared_->refcount = 1;
+    }
+
+    MemoryPoolAllocator(const MemoryPoolAllocator& rhs) RAPIDJSON_NOEXCEPT :
+        chunk_capacity_(rhs.chunk_capacity_),
+        baseAllocator_(rhs.baseAllocator_),
+        shared_(rhs.shared_)
+    {
+        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
+        ++shared_->refcount;
+    }
+    MemoryPoolAllocator& operator=(const MemoryPoolAllocator& rhs) RAPIDJSON_NOEXCEPT
+    {
+        RAPIDJSON_NOEXCEPT_ASSERT(rhs.shared_->refcount > 0);
+        ++rhs.shared_->refcount;
+        this->~MemoryPoolAllocator();
+        baseAllocator_ = rhs.baseAllocator_;
+        chunk_capacity_ = rhs.chunk_capacity_;
+        shared_ = rhs.shared_;
+        return *this;
+    }
+
+#if RAPIDJSON_HAS_CXX11_RVALUE_REFS
+    MemoryPoolAllocator(MemoryPoolAllocator&& rhs) RAPIDJSON_NOEXCEPT :
+        chunk_capacity_(rhs.chunk_capacity_),
+        baseAllocator_(rhs.baseAllocator_),
+        shared_(rhs.shared_)
+    {
+        RAPIDJSON_NOEXCEPT_ASSERT(rhs.shared_->refcount > 0);
+        rhs.shared_ = 0;
+    }
+    MemoryPoolAllocator& operator=(MemoryPoolAllocator&& rhs) RAPIDJSON_NOEXCEPT
+    {
+        RAPIDJSON_NOEXCEPT_ASSERT(rhs.shared_->refcount > 0);
+        this->~MemoryPoolAllocator();
+        baseAllocator_ = rhs.baseAllocator_;
+        chunk_capacity_ = rhs.chunk_capacity_;
+        shared_ = rhs.shared_;
+        rhs.shared_ = 0;
+        return *this;
+    }
+#endif
+
+    //! Destructor.
+    /*! This deallocates all memory chunks, excluding the user-supplied buffer.
+    */
+    ~MemoryPoolAllocator() RAPIDJSON_NOEXCEPT {
+        if (!shared_) {
+            // do nothing if moved
+            return;
+        }
+        if (shared_->refcount > 1) {
+            --shared_->refcount;
+            return;
+        }
+        Clear();
+        BaseAllocator *a = shared_->ownBaseAllocator;
+        if (shared_->ownBuffer) {
+            baseAllocator_->Free(shared_);
+        }
+        RAPIDJSON_DELETE(a);
+    }
+
+    //! Deallocates all memory chunks, excluding the first/user one.
+    void Clear() RAPIDJSON_NOEXCEPT {
+        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
+        for (;;) {
+            ChunkHeader* c = shared_->chunkHead;
+            if (!c->next) {
+                break;
+            }
+            shared_->chunkHead = c->next;
+            baseAllocator_->Free(c);
+        }
+        shared_->chunkHead->size = 0;
+    }
+
+    //! Computes the total capacity of allocated memory chunks.
+    /*! \return total capacity in bytes.
+    */
+    size_t Capacity() const RAPIDJSON_NOEXCEPT {
+        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
+        size_t capacity = 0;
+        for (ChunkHeader* c = shared_->chunkHead; c != 0; c = c->next)
+            capacity += c->capacity;
+        return capacity;
+    }
+
+    //! Computes the memory blocks allocated.
+    /*! \return total used bytes.
+    */
+    size_t Size() const RAPIDJSON_NOEXCEPT {
+        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
+        size_t size = 0;
+        for (ChunkHeader* c = shared_->chunkHead; c != 0; c = c->next)
+            size += c->size;
+        return size;
+    }
+
+    //! Whether the allocator is shared.
+    /*! \return true or false.
+    */
+    bool Shared() const RAPIDJSON_NOEXCEPT {
+        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
+        return shared_->refcount > 1;
+    }
+
+    //! Allocates a memory block. (concept Allocator)
+    void* Malloc(size_t size) {
+        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
+        if (!size)
+            return NULL;
+
+        size = RAPIDJSON_ALIGN(size);
+        if (RAPIDJSON_UNLIKELY(shared_->chunkHead->size + size > shared_->chunkHead->capacity))
+            if (!AddChunk(chunk_capacity_ > size ? chunk_capacity_ : size))
+                return NULL;
+
+        void *buffer = GetChunkBuffer(shared_) + shared_->chunkHead->size;
+        shared_->chunkHead->size += size;
+        return buffer;
+    }
+
+    //! Resizes a memory block (concept Allocator)
+    void* Realloc(void* originalPtr, size_t originalSize, size_t newSize) {
+        if (originalPtr == 0)
+            return Malloc(newSize);
+
+        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
+        if (newSize == 0)
+            return NULL;
+
+        originalSize = RAPIDJSON_ALIGN(originalSize);
+        newSize = RAPIDJSON_ALIGN(newSize);
+
+        // Do not shrink if new size is smaller than original
+        if (originalSize >= newSize)
+            return originalPtr;
+
+        // Simply expand it if it is the last allocation and there is sufficient space
+        if (originalPtr == GetChunkBuffer(shared_) + shared_->chunkHead->size - originalSize) {
+            size_t increment = static_cast<size_t>(newSize - originalSize);
+            if (shared_->chunkHead->size + increment <= shared_->chunkHead->capacity) {
+                shared_->chunkHead->size += increment;
+                return originalPtr;
+            }
+        }
+
+        // Realloc process: allocate and copy memory, do not free original buffer.
+        if (void* newBuffer = Malloc(newSize)) {
+            if (originalSize)
+                std::memcpy(newBuffer, originalPtr, originalSize);
+            return newBuffer;
+        }
+        else
+            return NULL;
+    }
+
+    //! Frees a memory block (concept Allocator)
+    static void Free(void *ptr) RAPIDJSON_NOEXCEPT { (void)ptr; } // Do nothing
+
+    //! Compare (equality) with another MemoryPoolAllocator
+    bool operator==(const MemoryPoolAllocator& rhs) const RAPIDJSON_NOEXCEPT {
+        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
+        RAPIDJSON_NOEXCEPT_ASSERT(rhs.shared_->refcount > 0);
+        return shared_ == rhs.shared_;
+    }
+    //! Compare (inequality) with another MemoryPoolAllocator
+    bool operator!=(const MemoryPoolAllocator& rhs) const RAPIDJSON_NOEXCEPT {
+        return !operator==(rhs);
+    }
+
+private:
+    //! Creates a new chunk.
+    /*! \param capacity Capacity of the chunk in bytes.
+        \return true if success.
+    */
+    bool AddChunk(size_t capacity) {
+        if (!baseAllocator_)
+            shared_->ownBaseAllocator = baseAllocator_ = RAPIDJSON_NEW(BaseAllocator)();
+        if (ChunkHeader* chunk = static_cast<ChunkHeader*>(baseAllocator_->Malloc(SIZEOF_CHUNK_HEADER + capacity))) {
+            chunk->capacity = capacity;
+            chunk->size = 0;
+            chunk->next = shared_->chunkHead;
+            shared_->chunkHead = chunk;
+            return true;
+        }
+        else
+            return false;
+    }
+
+    static inline void* AlignBuffer(void* buf, size_t &size)
+    {
+        RAPIDJSON_NOEXCEPT_ASSERT(buf != 0);
+        const uintptr_t mask = sizeof(void*) - 1;
+        const uintptr_t ubuf = reinterpret_cast<uintptr_t>(buf);
+        if (RAPIDJSON_UNLIKELY(ubuf & mask)) {
+            const uintptr_t abuf = (ubuf + mask) & ~mask;
+            RAPIDJSON_ASSERT(size >= abuf - ubuf);
+            buf = reinterpret_cast<void*>(abuf);
+            size -= abuf - ubuf;
+        }
+        return buf;
+    }
+
+    size_t chunk_capacity_;     //!< The minimum capacity of chunk when they are allocated.
+    BaseAllocator* baseAllocator_;  //!< base allocator for allocating memory chunks.
+    SharedData *shared_;        //!< The shared data of the allocator
+};
+
+namespace internal {
+    template<typename, typename = void>
+    struct IsRefCounted :
+        public FalseType
+    { };
+    template<typename T>
+    struct IsRefCounted<T, typename internal::EnableIfCond<T::kRefCounted>::Type> :
+        public TrueType
+    { };
+}
+
+template<typename T, typename A>
+inline T* Realloc(A& a, T* old_p, size_t old_n, size_t new_n)
+{
+    RAPIDJSON_NOEXCEPT_ASSERT(old_n <= SIZE_MAX / sizeof(T) && new_n <= SIZE_MAX / sizeof(T));
+    return static_cast<T*>(a.Realloc(old_p, old_n * sizeof(T), new_n * sizeof(T)));
+}
+
+template<typename T, typename A>
+inline T *Malloc(A& a, size_t n = 1)
+{
+    return Realloc<T, A>(a, NULL, 0, n);
+}
+
+template<typename T, typename A>
+inline void Free(A& a, T *p, size_t n = 1)
+{
+    static_cast<void>(Realloc<T, A>(a, p, n, 0));
+}
+
+#ifdef __GNUC__
+RAPIDJSON_DIAG_PUSH
+RAPIDJSON_DIAG_OFF(effc++) // std::allocator can safely be inherited
+#endif
+
+template <typename T, typename BaseAllocator = CrtAllocator>
+class StdAllocator :
+    public std::allocator<T>
+{
+    typedef std::allocator<T> allocator_type;
+#if RAPIDJSON_HAS_CXX11
+    typedef std::allocator_traits<allocator_type> traits_type;
+#else
+    typedef allocator_type traits_type;
+#endif
+
+public:
+    typedef BaseAllocator BaseAllocatorType;
+
+    StdAllocator() RAPIDJSON_NOEXCEPT :
+        allocator_type(),
+        baseAllocator_()
+    { }
+
+    StdAllocator(const StdAllocator& rhs) RAPIDJSON_NOEXCEPT :
+        allocator_type(rhs),
+        baseAllocator_(rhs.baseAllocator_)
+    { }
+
+    template<typename U>
+    StdAllocator(const StdAllocator<U, BaseAllocator>& rhs) RAPIDJSON_NOEXCEPT :
+        allocator_type(rhs),
+        baseAllocator_(rhs.baseAllocator_)
+    { }
+
+#if RAPIDJSON_HAS_CXX11_RVALUE_REFS
+    StdAllocator(StdAllocator&& rhs) RAPIDJSON_NOEXCEPT :
+        allocator_type(std::move(rhs)),
+        baseAllocator_(std::move(rhs.baseAllocator_))
+    { }
+#endif
+#if RAPIDJSON_HAS_CXX11
+    using propagate_on_container_move_assignment = std::true_type;
+    using propagate_on_container_swap = std::true_type;
+#endif
+
+    /* implicit */
+    StdAllocator(const BaseAllocator& allocator) RAPIDJSON_NOEXCEPT :
+        allocator_type(),
+        baseAllocator_(allocator)
+    { }
+
+    ~StdAllocator() RAPIDJSON_NOEXCEPT
+    { }
+
+    template<typename U>
+    struct rebind {
+        typedef StdAllocator<U, BaseAllocator> other;
+    };
+
+    typedef typename traits_type::size_type         size_type;
+    typedef typename traits_type::difference_type   difference_type;
+
+    typedef typename traits_type::value_type        value_type;
+    typedef typename traits_type::pointer           pointer;
+    typedef typename traits_type::const_pointer     const_pointer;
+
+#if RAPIDJSON_HAS_CXX11
+
+    typedef typename std::add_lvalue_reference<value_type>::type &reference;
+    typedef typename std::add_lvalue_reference<typename std::add_const<value_type>::type>::type &const_reference;
+
+    pointer address(reference r) const RAPIDJSON_NOEXCEPT
+    {
+        return std::addressof(r);
+    }
+    const_pointer address(const_reference r) const RAPIDJSON_NOEXCEPT
+    {
+        return std::addressof(r);
+    }
+
+    size_type max_size() const RAPIDJSON_NOEXCEPT
+    {
+        return traits_type::max_size(*this);
+    }
+
+    template <typename ...Args>
+    void construct(pointer p, Args&&... args)
+    {
+        traits_type::construct(*this, p, std::forward<Args>(args)...);
+    }
+    void destroy(pointer p)
+    {
+        traits_type::destroy(*this, p);
+    }
+
+#else // !RAPIDJSON_HAS_CXX11
+
+    typedef typename allocator_type::reference       reference;
+    typedef typename allocator_type::const_reference const_reference;
+
+    pointer address(reference r) const RAPIDJSON_NOEXCEPT
+    {
+        return allocator_type::address(r);
+    }
+    const_pointer address(const_reference r) const RAPIDJSON_NOEXCEPT
+    {
+        return allocator_type::address(r);
+    }
+
+    size_type max_size() const RAPIDJSON_NOEXCEPT
+    {
+        return allocator_type::max_size();
+    }
+
+    void construct(pointer p, const_reference r)
+    {
+        allocator_type::construct(p, r);
+    }
+    void destroy(pointer p)
+    {
+        allocator_type::destroy(p);
+    }
+
+#endif // !RAPIDJSON_HAS_CXX11
+
+    template <typename U>
+    U* allocate(size_type n = 1, const void* = 0)
+    {
+        return RAPIDJSON_NAMESPACE::Malloc<U>(baseAllocator_, n);
+    }
+    template <typename U>
+    void deallocate(U* p, size_type n = 1)
+    {
+        RAPIDJSON_NAMESPACE::Free<U>(baseAllocator_, p, n);
+    }
+
+    pointer allocate(size_type n = 1, const void* = 0)
+    {
+        return allocate<value_type>(n);
+    }
+    void deallocate(pointer p, size_type n = 1)
+    {
+        deallocate<value_type>(p, n);
+    }
+
+#if RAPIDJSON_HAS_CXX11
+    using is_always_equal = std::is_empty<BaseAllocator>;
+#endif
+
+    template<typename U>
+    bool operator==(const StdAllocator<U, BaseAllocator>& rhs) const RAPIDJSON_NOEXCEPT
+    {
+        return baseAllocator_ == rhs.baseAllocator_;
+    }
+    template<typename U>
+    bool operator!=(const StdAllocator<U, BaseAllocator>& rhs) const RAPIDJSON_NOEXCEPT
+    {
+        return !operator==(rhs);
+    }
+
+    //! rapidjson Allocator concept
+    static const bool kNeedFree = BaseAllocator::kNeedFree;
+    static const bool kRefCounted = internal::IsRefCounted<BaseAllocator>::Value;
+    void* Malloc(size_t size)
+    {
+        return baseAllocator_.Malloc(size);
+    }
+    void* Realloc(void* originalPtr, size_t originalSize, size_t newSize)
+    {
+        return baseAllocator_.Realloc(originalPtr, originalSize, newSize);
+    }
+    static void Free(void *ptr) RAPIDJSON_NOEXCEPT
+    {
+        BaseAllocator::Free(ptr);
+    }
+
+private:
+    template <typename, typename>
+    friend class StdAllocator; // access to StdAllocator<!T>.*
+
+    BaseAllocator baseAllocator_;
+};
+
+#if !RAPIDJSON_HAS_CXX17 // std::allocator<void> deprecated in C++17
+template <typename BaseAllocator>
+class StdAllocator<void, BaseAllocator> :
+    public std::allocator<void>
+{
+    typedef std::allocator<void> allocator_type;
+
+public:
+    typedef BaseAllocator BaseAllocatorType;
+
+    StdAllocator() RAPIDJSON_NOEXCEPT :
+        allocator_type(),
+        baseAllocator_()
+    { }
+
+    StdAllocator(const StdAllocator& rhs) RAPIDJSON_NOEXCEPT :
+        allocator_type(rhs),
+        baseAllocator_(rhs.baseAllocator_)
+    { }
+
+    template<typename U>
+    StdAllocator(const StdAllocator<U, BaseAllocator>& rhs) RAPIDJSON_NOEXCEPT :
+        allocator_type(rhs),
+        baseAllocator_(rhs.baseAllocator_)
+    { }
+
+    /* implicit */
+    StdAllocator(const BaseAllocator& baseAllocator) RAPIDJSON_NOEXCEPT :
+        allocator_type(),
+        baseAllocator_(baseAllocator)
+    { }
+
+    ~StdAllocator() RAPIDJSON_NOEXCEPT
+    { }
+
+    template<typename U>
+    struct rebind {
+        typedef StdAllocator<U, BaseAllocator> other;
+    };
+
+    typedef typename allocator_type::value_type value_type;
+
+private:
+    template <typename, typename>
+    friend class StdAllocator; // access to StdAllocator<!T>.*
+
+    BaseAllocator baseAllocator_;
+};
+#endif
+
+#ifdef __GNUC__
+RAPIDJSON_DIAG_POP
+#endif
+
+RAPIDJSON_NAMESPACE_END
+
+#endif // RAPIDJSON_ENCODINGS_H_