c – readyRead()在Qt中如何工作？

void QIODevice::readyRead() [signal]

This signal is emitted once every time new data is available for reading from the device. It will only be emitted again once new data is available,such as when a new payload of network data has arrived on your network socket,or when a new block of data has been appended to your device.

readyRead() is not emitted recursively; if you reenter the event loop or call waitForReadyRead() inside a slot connected to the readyRead() signal,the signal will not be reemitted (although waitForReadyRead() may still return true).

Note for developers implementing classes derived from QIODevice: you should always emit readyRead() when new data has arrived (do not emit it only because there’s data still to be read in your buffers). Do not emit readyRead() in other conditions.

这意味着它并没有真正保证可以读取多少数据,只是有些数据可用.

如果您希望读取的数据多于一次性输入的数据,则可以选择超时值和/或readyRead.这取决于你想要达到的目标.

请参阅我之前为此操作编写的command line async reader example：

#include "serialportreader.h"

#include <QCoreApplication>

QT_USE_NAMESPACE

SerialPortReader::SerialPortReader(QSerialPort *serialPort,QObject *parent)
    : QObject(parent),m_serialPort(serialPort),m_standardOutput(stdout)
{
    connect(m_serialPort,SLOT(handleReadyRead()));
    connect(m_serialPort,SIGNAL(error(QSerialPort::SerialPortError)),SLOT(handleError(QSerialPort::SerialPortError)));
    connect(&m_timer,SIGNAL(timeout()),SLOT(handleTimeout()));

    m_timer.start(5000);
}

SerialPortReader::~SerialPortReader()
{
}

void SerialPortReader::handleReadyRead()
{
    m_readData.append(m_serialPort->readAll());

    if (!m_timer.isActive())
        m_timer.start(5000);
}

void SerialPortReader::handleTimeout()
{
    if (m_readData.isEmpty()) {
        m_standardOutput << QObject::tr("No data was currently available for reading from port %1").arg(m_serialPort->portName()) << endl;
    } else {
        m_standardOutput << QObject::tr("Data successfully received from port %1").arg(m_serialPort->portName()) << endl;
        m_standardOutput << m_readData << endl;
    }

    QCoreApplication::quit();
}

void SerialPortReader::handleError(QSerialPort::SerialPortError serialPortError)
{
    if (serialPortError == QSerialPort::ReadError) {
        m_standardOutput << QObject::tr("An I/O error occurred while reading the data from port %1,error: %2").arg(m_serialPort->portName()).arg(m_serialPort->errorString()) << endl;
        QCoreApplication::exit(1);
    }
}

在这种情况下,命令行阅读器示例将获取一次性传递的任何数据,但不保证长度或任何内容.

此外,请注意您的评论背后的同步api与您询问的异步API一起没有多大意义.我指的是m_serialPort-> waitForReadyRead(200);在这里.