#include <QUdpSocket>// UDP 接受的数据char buf[1024] = { 0 };// 接受到数据的标识bool bRecvFlag = false;//Udp服务器QUdpSocket* mSocket;//通信的ip和端口，用于获取发送者的 IP 和端口QHostAddress sendAddr; // 本机QHostAddress recAddr;  // 设备ipquint16 recPort;quint16 sendPort;bool XXXCard::init() {mSocket = new QUdpSocket(this);// 发送指令的机器所在ip和端口QSettings ini_config("ICCardReader.ini", QSettings::IniFormat);ini_config.setIniCodec(QTextCodec::codecForName("utf-8"));ini_config.beginGroup("XXX");QString sendIP = ini_config.value("sendIP").toString();// 监听error()信号 不要监听这个，mSocket->waitForReadyRead会走到监听的槽函数里// connect(mSocket, SIGNAL(error(QAbstractSocket::SocketError)), this, SLOT(handleError(QAbstractSocket::SocketError)));//sendAddr.setAddress("192.168.1.2");sendAddr.setAddress(sendIP.isEmpty()?"192.168.1.2": sendIP);QString sendPortStr = ini_config.value("sendPort").toString();sendPortStr = sendPortStr.isEmpty() ? "8080" : sendPortStr;sendPort = sendPortStr.toInt();bool bRet = mSocket->bind(sendPort);// 接受指令的设备所在ip和端口 会返回响应报文QString cardIP = ini_config.value("cardIP").toString();recAddr.setAddress(cardIP.isEmpty() ? "192.168.1.232": cardIP);QString cardPortStr = ini_config.value("cardPort").toString();cardPortStr = cardPortStr.isEmpty() ? "8080" : cardPortStr;recPort = cardPortStr.toInt();// recPort = 8080;//  connect(mSocket, &QUdpSocket::readyRead, this, &HYB502Card::recvData);return bRet;
}// 发送二进制指令 0成功 其他返回错误
int XXXX::send_hex(const std::string& in, std::string& out) {outPutMsg(QtDebugMsg, "XXXX::send_hex invoke begin.req = " + QString(QString::fromLocal8Bit(in.c_str())));ss = "";response = "";QString qstr = QString::fromStdString(in);QByteArray baReq = qstr.toLocal8Bit();mSocket->writeDatagram(baReq, recAddr, recPort);bool flag = true;int i = 30;while (flag & i > 0){i--;Sleep(50);if (!mSocket->waitForReadyRead(10)) {continue;}quint16 port = 0;qint64 size = mSocket->readDatagram(buf, sizeof(buf), &sendAddr, &sendPort);if (size < 1) {continue;}out = buf;flag = false;  }QString res = QString::fromLocal8Bit(out.c_str());outPutMsg(QtDebugMsg, "APDU res = " + res);// pcsc_receiveBufferLen -= 2;//接受数据长度减去swint l_res = -1;if (out.length() >= 4) {ss = out.substr(out.length() - 4);response = out.substr(0, out.length() - 4);l_res = 0;}outPutMsg(QtDebugMsg, "XXXX::send_hex invoke end.");return l_res;
}

这里很多让用信号槽的方式接受返回的信息 .connect(mSocket, &QUdpSocket::readyRead, this, &HYB502Card::recvData); 实际使用中发现不好使（我查的是说发送一直占用焦点什么的，导致不会捕获到信号啥的），所以使用readDatagram直接从缓存里获取。

connect(mSocket, &QUdpSocket::readyRead, this, &HYB502Card::recvData);方式感觉比较适合单纯的接收或者发，不适合一边发一边收；

可能我理解的不准确，欢迎指正！