rfcomm0 read fails in Qt

[raedbenz]

Hello,

I have managed to open and read /dev/rfcomm0 using a simple C app i worte, using fopen, fread and fwrite, on Ubuntu 10.04.
now i want to do that in Qt.
I managed to open the file (doesnt fail in first 2 checks), but returns 0 on number of bytes available for read. and if i skip bytesAvailable() and just read the device it gets stuck there infinitely. hints plz in opening reading device files using QT?
here is the code. i tried that as well on N900 and same. Thanks in advance.

#include <QApplication>
#include <QFile>
#include <QDebug>
#include <QLabel>
#include <QIODevice>
 
QIODevice *fd; //i tried QFile as well but no success
 
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QLabel hello("Hello world!");
    qint64 i;
    QByteArray ba;
    fd = new QFile("/dev/rfcomm0");
 
    hello.resize(300, 100);
    hello.show();
 
    if( !fd->open(QIODevice::ReadWrite) )
    {
        qDebug() << "Failed opening";
        return 0;
    }
 
    if( !fd->isReadable() )
    {
        qDebug() << "Not Readable";
        return 0;
    }
 
    qDebug() << "Please Wait";
    sleep(1);
 
    i = fd->bytesAvailable();
    qDebug() << "i:" << i;
 
    if(i == 0)
    {
        return 0;
    }
 
    ba = fd->read(1);
    qDebug() << "DATA:" << ba;
 
    fd->close();
 
    return app.exec();
}

#include <QApplication>
#include <QFile>
#include <QDebug>
#include <QLabel>
#include <QIODevice>

QIODevice *fd; //i tried QFile as well but no success


int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QLabel hello("Hello world!");
    qint64 i;
    QByteArray ba;
    fd = new QFile("/dev/rfcomm0");

    hello.resize(300, 100);
    hello.show();

    if( !fd->open(QIODevice::ReadWrite) )
    {
        qDebug() << "Failed opening";
        return 0;
    }

    if( !fd->isReadable() )
    {
        qDebug() << "Not Readable";
        return 0;
    }

    qDebug() << "Please Wait";
    sleep(1);

    i = fd->bytesAvailable();
    qDebug() << "i:" << i;

    if(i == 0)
    {
        return 0;
    }

    ba = fd->read(1);
    qDebug() << "DATA:" << ba;

    fd->close();

    return app.exec();
}

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[wysota]

Is there any data to read in rfcomm? You might use QSocketNotifier to check that out before you do any reading.

[raedbenz]

Is there any data to read in rfcomm? You might use QSocketNotifier to check that out before you do any reading.

yes,,,i have managed to read it using a test app in C using fopen and fread. any alternative QT API or initialization to do in before reading device file?
thanx

[raedbenz]

the only way i found to get around is by using in my Qt example the C functions fopen, fread and fwrite.
if you know how to open read a device file in Qt plz let me know.

--------------------------------------
http://howinuk.co.uk

[wysota]

Did you try QSocketNotifier and QLocalSocket?

[raedbenz]

Did you try QSocketNotifier and QLocalSocket?

hello i tried QSocketNotifier as follows:

fd = new QFile("/dev/rfcomm0");
i = fd->open(QIODevice::ReadOnly);
note = new QSocketNotifier(i, QSocketNotifier::Read,this);
connect(note, SIGNAL(activated(int)), this, SLOT(sighndl()));

fd = new QFile("/dev/rfcomm0");
i = fd->open(QIODevice::ReadOnly);
note = new QSocketNotifier(i, QSocketNotifier::Read,this);
connect(note, SIGNAL(activated(int)), this, SLOT(sighndl()));

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but no luck, regarding QLocalSocket i cant use it because "This class is not part of the Qt GUI Framework Edition."
any further ideas?
thanks

[wysota]

hello i tried QSocketNotifier as follows:

fd = new QFile("/dev/rfcomm0");
i = fd->open(QIODevice::ReadOnly);
note = new QSocketNotifier(i, QSocketNotifier::Read,this);
connect(note, SIGNAL(activated(int)), this, SLOT(sighndl()));

fd = new QFile("/dev/rfcomm0");
i = fd->open(QIODevice::ReadOnly);
note = new QSocketNotifier(i, QSocketNotifier::Read,this);
connect(note, SIGNAL(activated(int)), this, SLOT(sighndl()));

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but no luck

QFile::open() returns a bool saying if the file was opened or not and you are passing it as a socket descriptor to QSocketNotifier. This hardly has a chance to work

, regarding QLocalSocket i cant use it because "This class is not part of the Qt GUI Framework Edition."

So why can't you use it exactly?

[raedbenz]

QFile::open() returns a bool saying if the file was opened or not and you are passing it as a socket descriptor to QSocketNotifier. This hardly has a chance to work


So why can't you use it exactly?

hello, thanks for the reply.
the reason i cant use QLocalSocket is the compiler gives an error:

error: QLocalSocket: No such file or directory

although #include <QLocalSocket> is added , any hints?

one more thing, the first argument of QSocketNotifier is a socket identifier of type integer, so how can i pass the correct argument since socket function is not part of QFile or QIODevice?
do i have to cast file descriptor ?
Thanks

[wysota]

hello, thanks for the reply.
the reason i cant use QLocalSocket is the compiler gives an error:

although #include <QLocalSocket> is added , any hints?

Did you enable the QtNetwork module?

one more thing, the first argument of QSocketNotifier is a socket identifier of type integer, so how can i pass the correct argument since socket function is not part of QFile or QIODevice?

You have to get the file descriptor that you can pass there (i.e. one returned by ::open()

[raedbenz]

Did you enable the QtNetwork module?


You have to get the file descriptor that you can pass there (i.e. one returned by :pen()

hello,
how do i enable QtNetwork module? do i add #include <QtNetwork> and to project file 'QT += network' ?

thanx

[wysota]

do i add #include <QtNetwork> and to project file 'QT += network' ?

Wouldn't it be faster to actually do that and see for yourself instead of writing this post here?

[raedbenz]

Hello,
i managed to read data using QSocketNotifier and it works fine, here is the code snippet:

QSocketNotifier *note;
int socfd;
socfd = open("/dev/rfcomm0", O_RDONLY|O_NONBLOCK);
note = new QSocketNotifier(socfd, QSocketNotifier::Read, this);
connect(note, SIGNAL(activated(int)), this, SLOT(readbytes()));

QSocketNotifier *note;
int socfd;
socfd = open("/dev/rfcomm0", O_RDONLY|O_NONBLOCK);
note = new QSocketNotifier(socfd, QSocketNotifier::Read, this);
connect(note, SIGNAL(activated(int)), this, SLOT(readbytes()));

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but still cant manage to open the device file using QLocalSocket.
what i did is:

QLocalSocket *Socket;
Socket = new QLocalSocket(this);
Socket->connectToServer("/dev/rfcomm0", QIODevice::ReadOnly);
connect(Socket, SIGNAL(readyRead()), this, SLOT(readSocket()));

QLocalSocket *Socket;
Socket = new QLocalSocket(this);
Socket->connectToServer("/dev/rfcomm0", QIODevice::ReadOnly);
connect(Socket, SIGNAL(readyRead()), this, SLOT(readSocket()));

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the connections was not established at all. any hints?
Thanks