近日要用Qt设计路灯节能监控系统的上位机，用到QTcpSocket类，参考文档英文的，看起来不方便，按学习笔记的方式，归纳如下：

1. enum QAbstractSocket::NetworkLayerProtocol

This enum describes the network layer protocol values used in Qt.

Constant Value Description QAbstractSocket::IPv4Protocol QAbstractSocket::IPv6Protocol QAbstractSocket::UnknownNetworkLayerProtocol Other than IPv4 and IPv6   列出了Qt使用的网络层次协议，如IP4，IP6.

2.enum QIODevice::OpenModeFlag
flags QIODevice::OpenMode

This enum is used with open () to describe the mode in which a device is opened. It is also returned by openMode ().

Constant Value Description QIODevice::NotOpen 0x0000 The device is not open. QIODevice::ReadOnly 0x0001 The device is open for reading. QIODevice::WriteOnly 0x0002 The device is open for writing. QIODevice::ReadWrite ReadOnly | WriteOnly The device is open for reading and writing. QIODevice::Append 0x0004 The device is opened in append mode, so that all data is written to the end of the file. QIODevice::Truncate 0x0008 If possible, the device is truncated before it is opened. All earlier contents of the device are lost. QIODevice::Text 0x0010 When reading, the end-of-line terminators are translated to '\n'. When writing, the end-of-line terminators are translated to the local encoding, for example '\r\n' for Win32. QIODevice::Unbuffered 0x0020 Any buffer in the device is bypassed. QAbstractSocket::ConnectionRefusedError The connection was refused by the peer (or timed out). QAbstractSocket::RemoteHostClosedError The remote host closed the connection. Note that the client socket (i.e., this socket) will be closed after the remote close notification has been sent. QAbstractSocket::HostNotFoundError The host address was not found. QAbstractSocket::SocketAccessError The socket operation failed because the application lacked the required privileges. QAbstractSocket::SocketResourceError The local system ran out of resources (e.g., too many sockets). QAbstractSocket::SocketTimeoutError The socket operation timed out. QAbstractSocket::DatagramTooLargeError The datagram was larger than the operating system's limit (which can be as low as 8192 bytes). QAbstractSocket::NetworkError An error occurred with the network (e.g., the network cable was accidentally plugged out). QAbstractSocket::AddressInUseError The address specified to QUdpSocket::bind () is already in use and was set to be exclusive. QAbstractSocket::SocketAddressNotAvailableError The address specified to QUdpSocket::bind () does not belong to the host. QAbstractSocket::UnsupportedSocketOperationError The requested socket operation is not supported by the local operating system (e.g., lack of IPv6 support). QAbstractSocket::ProxyAuthenticationRequiredError The socket is using a proxy, and the proxy requires authentication. QAbstractSocket::SslHandshakeFailedError The SSL/TLS handshake failed, so the connection was closed (only used in QSslSocket ) QAbstractSocket::UnfinishedSocketOperationError Used by QAbstractSocketEngine only, The last operation attempted has not finished yet (still in progress in the background). QAbstractSocket::ProxyConnectionRefusedError Could not contact the proxy server because the connection to that server was denied QAbstractSocket::ProxyConnectionClosedError The connection to the proxy server was closed unexpectedly (before the connection to the final peer was established) QAbstractSocket::ProxyConnectionTimeoutError The connection to the proxy server timed out or the proxy server stopped responding in the authentication phase. QAbstractSocket::ProxyNotFoundError The proxy address set with setProxy () (or the application proxy) was not found. QAbstractSocket::ProxyProtocolError The connection negotiation with the proxy server because the response from the proxy server could not be understood. QAbstractSocket::UnknownSocketError An unidentified error occurred. QAbstractSocket::ClosingState The socket is about to close (data may still be waiting to be written). QAbstractSocket::ListeningState For internal use only.