无缓冲 std Streambuf 实现
为了对序列化库进行一些快速测试，我想创建一个可以从套接字读取/写入的streambuf。我不想在streambuf中使用缓冲区，而是让套接字处理这个问题。我确信序列化库只会调用 std::istream::read 和 std::ostream::write 。快速浏览一下 Microsoft 的 basic_streambuf 实现就会发现，这些调用实际上直接转发到 xsputn 和 xsgetn。
问题是：我可以从streambuf派生并仅实现xsputn和xsgetn，并确保使用我的实现的流将始终调用这些方法，而不是sync/overflow/underflow/pback/...？或者我应该覆盖同步等以返回错误，或者标准是否保证默认实现没问题？最好这应该在任何通用平台上工作，并且我不能使用 boost::iostreams。
实际上我会使用这样的东西：
class socket_buf : public std::streambuf
{
public:
//Socket is a class with std::stream-like read/write methods
MyBuf( Socket& s ) : sock( s ) {}
protected:
std::streamsize xsputn( const char* s, std::streamsize n )
{
return sock.write( s, n );
}
std::streamsize xsgetn( char* s, std::streamsize n )
{
return sock.read( s, n );
}
private:
Socket& sock;
};
for some quick testing of a serialization library I want to create a streambuf that can read/write to/from a socket. I do not want to use a buffer in the streambuf, but let the socket handle this. I am sure the serialization lib will only call std::istream::read and std::ostream::write. A quick look at Microsoft's basic_streambuf implementation shows that these calls are practically directly forwarded to xsputn and xsgetn.
The question is: can I derive from a streambuf and just implement xsputn and xsgetn, and be sure that the streams that use my implementation will always call these methods, and not sync/overflow/underflow/pback/... ? Or else should I override sync etc to return errors, or does the standard guarantee that the default implementations are fine? Preferrably this should work on any common platform, and I cannot use the boost::iostreams.
Practically I'd use something like this:
class socket_buf : public std::streambuf
{
public:
//Socket is a class with std::stream-like read/write methods
MyBuf( Socket& s ) : sock( s ) {}
protected:
std::streamsize xsputn( const char* s, std::streamsize n )
{
return sock.write( s, n );
}
std::streamsize xsgetn( char* s, std::streamsize n )
{
return sock.read( s, n );
}
private:
Socket& sock;
};
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如果没有缓冲区，（几乎？）不可能实现 std::streambuf。您必须重载
underflow和overflow，因为std::streambuf的许多公共接口不会通过xsputn< /code> 或xsgetn。例如sputc、sbumpc等。甚至sputn也不能保证引起调用xsputn，具体取决于xsputn的状态内部缓冲区和特定的 std::streambuf 实现。It's (almost?) impossible to implement a
std::streambufwithout a buffer. You will have to overloadunderflowandoverflowas many of the public interfaces tostd::streambufwon't go viaxsputnorxsgetn. E.g.sputc,sbumpc, etc. Evensputnis not guaranteed to cause a callxsputndepending on the state of the internal buffer and the particularstd::streambufimplementation.