c++ - 错误 C2582: 'operator =' 函数在 'bitstream::bitset_extractor VS 2010 中不可用

Question

我遇到了一个奇怪的问题。相同的代码在 vs 2008 和 VS 2010 Debug 和 Dubug Unicode 版本中运行良好，但在 Release 和 Release Unicode 中编译失败。这可能是什么原因。

这段代码产生了错误

struct bitset_extractor
{
    typedef std::forward_iterator_tag   iterator_category;
    typedef T                           value_type;
    typedef T*                          pointer;
    typedef T&                          reference;
    typedef ptrdiff_t                   difference_type;

    bitset_extractor(const boost::dynamic_bitset<T>& bs, T *buffer)
        : bs_(bs), buffer_(buffer), current_(0)
    {}

    bitset_extractor(const bitset_extractor& it)
        : bs_(it.bs_), buffer_(it.buffer_), current_(it.current_)
    {}

    T& operator*()
    {
        return buffer_[current_];
    }

    bitset_extractor& operator++()
    {
        ++current_;
        return *this;
    }
   private:
    void operator=(T const&);           // unimplemented

    const boost::dynamic_bitset<T>&     bs_;
    T * const                           buffer_;
    unsigned int                        current_;
};

1>C:\Program Files\Microsoft Visual Studio 10.0\VC\include\xutility(275): error C2679: binary '=' : no operator found which takes a right-hand operand of type 'bitstream::bitset_extractor<T>' (or there is no acceptable conversion)
1>          with
1>          [
1>              T=uint8_t
1>          ]
1>           C:\vikram\Project\Seurat\src\app\logitech\LogiRTP\Library\Filters\plc\common\bitstream.h(195): could be 'void bitstream::bitset_extractor<T>::operator =(const T &)'
1>          with
1>          [
1>              T=uint8_t
1>          ]
1>          while trying to match the argument list '(bitstream::bitset_extractor<T>, bitstream::bitset_extractor<T>)'
1>          with
1>          [
1>              T=uint8_t
1>          ]
1>          C:\Program Files\Microsoft Visual Studio 10.0\VC\include\xutility(2176) : see reference to function template instantiation '_Iter &std::_Rechecked<_OutIt,_OutIt>(_Iter &,_UIter)' being compiled
1>          with
1>          [
1>              _Iter=bitstream::bitset_extractor<uint8_t>,
1>              _OutIt=bitstream::bitset_extractor<uint8_t>,
1>              _UIter=bitstream::bitset_extractor<uint8_t>
1>          ]
1>          C:\vikram\Project\Seurat\3rdparty\boost\boost/dynamic_bitset/dynamic_bitset.hpp(1090) : see reference to function template instantiation '_OutIt std::copy<std::_Vector_const_iterator<_Myvec>,BlockOutputIterator>(_InIt,_InIt,_OutIt)' being compiled
1>          with
1>          [
1>              _OutIt=bitstream::bitset_extractor<uint8_t>,
1>              _Myvec=std::_Vector_val<unsigned char,std::allocator<uint8_t>>,
1>              BlockOutputIterator=bitstream::bitset_extractor<uint8_t>,
1>              _InIt=std::_Vector_const_iterator<std::_Vector_val<unsigned char,std::allocator<uint8_t>>>
1>          ]
1>          C:\vikram\Project\Seurat\src\app\logitech\LogiRTP\Library\Filters\plc\common\bitstream.h(210) : see reference to function template instantiation 'void boost::to_block_range<uint8_t,std::allocator<_Ty>,bitstream::bitset_extractor<T>>(const boost::dynamic_bitset<Block> &,BlockOutputIterator)' being compiled
1>          with
1>          [
1>              _Ty=uint8_t,
1>              T=uint8_t,
1>              Block=uint8_t,
1>              BlockOutputIterator=bitstream::bitset_extractor<uint8_t>
1>          ]
1>C:\Program Files\Microsoft Visual Studio 10.0\VC\include\xutility(275): error C2582: 'operator =' function is unavailable in 'bitstream::bitset_extractor<T>'
1>          with
1>          [
1>              T=uint8_t
1>          ]

Answer 1

问题是你的 bitset_extractor被用作迭代器，但它不满足迭代器的所有要求。

std::copy函数正在调用 operator=有两个bitset_extractor<uint8_t>对象，因为它试图将原始迭代器转换为已检查的迭代器。由于用户定义的迭代器不存在检查迭代器，检查迭代器类型和原始迭代器类型相同，导致使用迭代器的常规拷贝。

罪魁祸首是 _Rechecked函数，用于将常规迭代器转换为检查迭代器。根据迭代器调试级别，这是不同的做法；这就是为什么您的 Debug 构建有效，但您的 Release 构建无效，因为默认情况下它们具有不同的迭代器调试级别。

解决方案是实现operator=对于 bitset_extractor .如果您想将它用作迭代器，它必须支持其类型的迭代器所需的所有功能。

禁用已检查的迭代器无济于事。您的迭代器仍将通过 _Rechecked功能，无论你做什么。