c++ - 为遗留 C 链表接口(interface)提供 C++ 迭代器

Question

我有一个 Visual Studo 2008 C++ 应用程序，我试图在其中向遗留 C-API 的链表结构添加迭代器支持。 C 接口(interface)如下所示:

typedef struct _LINKED_LIST_INFO {
    struct _LINKED_LIST_INFO* Next;
    const char* name;
    // more elements. some are fixed-size; others are pointers to other structures.
} LINKED_LIST_INFO;

DWORD GetLinkedList( LINKED_LIST_INFO* pInfo, PULONG pOutBufLen );

我希望能够像这样使用它:

int _tmain( int /*argc*/, _TCHAR* /*argv*/[] )
{
    MyLinkedList elements;
    for( MyLinkedList::const_iterator it = elements.begin();
         it != elements.end();
         ++it )
    {
        printf( "Name: %s\r\n", it->Name().c_str() );
    }

    return 0;
}

所以，我创建了这 3 个类。但是，我的 MyInfoIterator 类的 operator->() 有问题。我无法返回指向 MyInfo 的临时指针，因此出现错误:error C2440: 'return' : cannot convert from 'MyInfo' to 'const MyInfo *'

这个问题有什么好的解决方案？

/// wrap the legacy C structure and provide C++ accessors
class MyInfo
{
public:

    MyInfo( const LINKED_LIST_INFO& info ) : elem_( info ) { };

    std::string Name() const { return elem_.name; };

private:
    /// one element of the linked list
    const LINKED_LIST_INFO& elem_;
}; // class MyInfo

namespace detail {

/// buffer to hold the legacy C linked-list
typedef std::vector< BYTE > MyBuffer;

/// iterator support for the legacy C linked-list
class MyInfoIterator 
    : public std::iterator< std::input_iterator_tag, MyInfo > 
{
public:
    explicit MyInfoIterator( MyBuffer& list ) : data_( list )
    {
        elem_ = reinterpret_cast< LINKED_LIST_INFO* >( &data_.front() );
    };

    MyInfoIterator() : elem_( NULL ) { };

    MyInfoIterator& operator++() 
    {
        elem_ = elem_->Next;
        return *this;
    };

    value_type operator*() { return *elem_; };

    //  error C2440: 'return' : cannot convert from 'MyInfo' to 'const MyInfo *'
    const value_type* operator->() { return elem_; };

    friend bool operator==( const MyInfoIterator& i, 
                            const MyInfoIterator& j ) 
    { 
        return i.elem_ == j.elem_;
    };

private:

    /// linked-list of elements
    MyBuffer data_;

    /// current position within the element list
    LINKED_LIST_INFO* elem_;

}; // class MyInfoIterator

bool operator!=( const MyInfoIterator& i, const MyInfoIterator& j ) 
{ 
    return !operator==( i, j );
}

}; // namespace detail

/// provide iterator access for the legacy C linked-list API
class MyLinkedList
{
public:
    typedef detail::MyInfoIterator const_iterator;

    const_iterator begin() const 
    { 
        ULONG size = sizeof( LINKED_LIST_INFO );
        detail::MyBuffer buffer( size );

        DWORD ec = ::GetLinkedList( 
            reinterpret_cast< LINKED_LIST_INFO* >( &buffer.front() ), &size );
        if( ERROR_BUFFER_OVERFLOW == ec )
        {
            buffer.resize( size );
            ec = ::GetLinkedList( 
                reinterpret_cast< LINKED_LIST_INFO* >( &buffer.front() ), &size );
        }

        if( ERROR_SUCCESS != ec )
            Win32Exception::Throw( ec );

        return const_iterator( buffer ); 
    };

    const_iterator end() const { return const_iterator(); };

}; // class MyInfo

谢谢，保罗H

编辑:

我无法更改遗留 API 或其关联结构。

编辑2:

我想我有一个可行的解决方案，它保留了我隐藏底层链表实现的意图，并通过返回 static MyInfo 的地址来维护每个类的职责分离。

class MyInfo
{
   // ...
protected:
    MyInfo() : info_( NULL ) { };
    void Set( const LINKED_LIST_INFO* info ) { info_ = info; };
private:
    friend MyInfoIterator;
    const LINKED_LIST_INFO* info_;
};

const value_type& MyInfoIterator::operator*() const 
{ 
    static MyInfo info;
    info.Set( elem_ );
    return info;
};

const value_type* MyInfoIterator::operator->() const
{ 
    static MyInfo info;
    info.Set( elem_ );
    return &info; 
};

Answer 1

保持简单:

class MyInfoIterator 
    : public std::iterator< std::input_iterator_tag, _LINKED_LIST_INFO >
{
   _LINKED_LIST_INFO* p;
public;
    MyInfoIterator(_LINKED_LIST_INFO* pointer) : p(pointer) {}

    [Same as you did]

    value_type& operator*() { return *p; }
}