check IPAddress existence

[navi1084]

Hi,

Can anyone tell me how can i retrieve information, whether a particular ipaddress is present or not within the subnet my pc is connected. using QTcpSocket i can use waitforconnection(). But i need quick response. Is there any Qt api to find.???

Thank you in advance

[spirit]

take a look at QHostInfo.

[navi1084]

Thanks you.
Yeah I already checked the same... But this will be used for mapping Name-IP pair right. how can i use this whether host is present or not

[spirit]

by looking at QHostInfo::error, it should return QHostInfo::HostNotFound or you can use ping + QProcess.

[navi1084]

Hi I tried this also. But i always get host is not found error. can you please give me a sample code to accomplish this. IP Address is 192.168.99.99

[spirit]

try something like this

...
QProcess *ping = new QProcess(this);
connect(ping, SIGNAL(readyReadStandardOutput()), SLOT(readResult()));
ping->start(QString("ping.exe %1").arg("192.168.99.99"));
...
void Test::readResult()
{
	QProcess *ping = qobject_cast<QProcess *>(sender());
	if (!ping)
		return;
	QString res = ping->readAllStandardOutput();
	if (!res.contains('%'))
		return;
	const int percent = res.mid(res.indexOf('('), res.indexOf(')')).section('%', 0, 0).remove('(').toInt();
	if (percent == 100) {
		qDebug() << "host not found.";
	} else {
		qDebug() << "host found.";
	}
}

...
QProcess *ping = new QProcess(this);
connect(ping, SIGNAL(readyReadStandardOutput()), SLOT(readResult()));
ping->start(QString("ping.exe %1").arg("192.168.99.99"));
...
void Test::readResult()
{
	QProcess *ping = qobject_cast<QProcess *>(sender());
	if (!ping)
		return;
	QString res = ping->readAllStandardOutput();
	if (!res.contains('%'))
		return;
	const int percent = res.mid(res.indexOf('('), res.indexOf(')')).section('%', 0, 0).remove('(').toInt();
	if (percent == 100) {
		qDebug() << "host not found.";
	} else {
		qDebug() << "host found.";
	}
}

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PS. it's for Windows.

[bmanam]

For folks running into raw socket creation permission issues, I'd recommend using fping which has many useful switches and utilizes the ICMP.dll to get around the permission problem.

[soukupmi]

spirit's code expanded (did not catch the TTL-expired case):

...
QProcess *ping = new QProcess(this);
connect(ping, SIGNAL(readyReadStandardOutput()), SLOT(readResult()));
ping->start(QString("ping.exe %1").arg("192.168.99.99"));
...
void Test::readResult()
{
    QProcess *ping = qobject_cast<QProcess *>(sender());
    if (!ping)
        return;
    QString res = ping->readAllStandardOutput();
    if (!res.contains('%'))
        return;
    const int percentLost = res.section('(', -1).section('%', 0, 0).toInt();
    if (percentLost == 100) {
        qDebug() << "host not found.";
    } else {
        // above is basically the same code until here:
	if ( res.contains(QRegExp("=\\d+ms")) ) {
	    qDebug() << "host found." << res; 		// actual response time from IP
	} else {
	    qDebug() << "host not found." << res; 	// TTL expired in transit
	}
    }
}

...
QProcess *ping = new QProcess(this);
connect(ping, SIGNAL(readyReadStandardOutput()), SLOT(readResult()));
ping->start(QString("ping.exe %1").arg("192.168.99.99"));
...
void Test::readResult()
{
    QProcess *ping = qobject_cast<QProcess *>(sender());
    if (!ping)
        return;
    QString res = ping->readAllStandardOutput();
    if (!res.contains('%'))
        return;
    const int percentLost = res.section('(', -1).section('%', 0, 0).toInt();
    if (percentLost == 100) {
        qDebug() << "host not found.";
    } else {
        // above is basically the same code until here:
	if ( res.contains(QRegExp("=\\d+ms")) ) {
	    qDebug() << "host found." << res; 		// actual response time from IP
	} else {
	    qDebug() << "host not found." << res; 	// TTL expired in transit
	}
    }
}

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[ChrisW67]

There is no guaranteed way to determine if a particular IP address is in use from a high level program. On a LAN you might be able to use ping or attempt to connect to a well known service that these machines might offer but many machines firewall these by default now.

You can use ARP to find if a machine claims the address, or query the system ARP table after attempting to connect another way. There is no Qt mechanism for doing this.