我正在尝试创建我的类,它只是从 boost::asio::streambuf
派生的公共(public)派生类,并添加了一些方法:
class my_super_streambuf : public boost::asio::streambuf {
public:
void my_super_method();
};
但是当我简单地将 boost::asio::streambuf
替换为 my_super_streambuf
时,出现了错误:
error C2039: 'const_iterator' : is not a member of 'my_super_streambuf'
在
D:\projects\my_super_streambuf\third-party\boost\boost/asio/impl/write.hpp(199) :
see reference to class template instantiation
'boost::asio::detail::consuming_buffers<boost::asio::const_buffer,
ConstBufferSequence>' being compiled
如何正确地从 boost::asio::streambuf
派生?
最佳答案
问题不在于如何派生自 boost::asio::streambuf
.相反,产生的错误是因为编译器选择了非流缓冲 write(SyncWriteStream&, const ConstBufferSequence&)
重载而不是 write(SyncWriteStream&, basic_streambuf<Allocator>&)
.要解决此问题,可以显式转换派生自 boost::asio::streambuf
的对象。引用 boost::asio::streambuf
调用时 write()
:
class derived_streambuf
: public boost::asio::streambuf
{};
// ...
derived_streambuf streambuf;
boost::asio::write(socket, static_cast<boost::asio::streambuf&>(streambuf));
要理解这个问题,请考虑有问题的重载函数的声明:
// ConstBufferSequence
template<
typename SyncWriteStream,
typename ConstBufferSequence>
std::size_t write(
SyncWriteStream&,
const ConstBufferSequence&);
// Streambuf
template<
typename SyncWriteStream,
typename Allocator>
std::size_t write(
SyncWriteStream&,
basic_streambuf<Allocator>&);
如果derived_streambuf
作为第二个参数提供,函数的实例化将导致:
// ConstBufferSequence
std::size_t write(..., derived_streambuf&);
// Streambuf
std::size_t write(..., basic_streambuf<char>&);
就编译器而言,第一个是更好的匹配,因为它是精确匹配,因此选择它。
这是一个完整的例子demonstrating编译代码:
#include <boost/asio.hpp>
// Derive from boost::asio::streambuf.
class derived_streambuf
: public boost::asio::streambuf
{};
// Helper function to force type.
template <typename Allocator>
boost::asio::basic_streambuf<Allocator>&
as_streambuf(boost::asio::basic_streambuf<Allocator>& streambuf)
{
return streambuf;
}
int main()
{
boost::asio::io_service io_service;
boost::asio::ip::tcp::socket socket(io_service);
derived_streambuf streambuf;
boost::asio::write(socket, static_cast<boost::asio::streambuf&>(streambuf));
boost::asio::write(socket, as_streambuf(streambuf));
}
关于c++ - 来自 `boost::asio::streambuf`,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/31423582/