引发错误的代码段：

QDataStream tempWriteDataStream(socket);

tempWriteDataStream.setVersion(QDataStream::Qt_5_14);

tempWriteDataStream << str;

socket->waitForBytesWritten();//此处报错

如果socket的状态为QLocalSocket::UnconnectedState，程序就会报QWindowsPipeWriter::write failed. (句柄无效。)

如果socket的状态为QLocalSocket::ConnectedState，则问题不会出现。

结论：一定要检查好socket的状态