Hello Tim,
In that case you could use the -q option as well and check for 0 return
status, e.g.
x = system("grep -cq \'^S:.*DeviceName\' /proc/bus/usb/devices");
if (x==0) ...; #found
Opening the file for reading and scanning the contents is also an option,
just a little more work on your part.
Best regards,
Edward
----- Original Message -----
From: "Tim Arney" <[EMAIL PROTECTED]>
To: "Edward" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Sent: Friday, November 19, 2004 01:19
Subject: Re: [Linux-usb-users] Detecting unplugged device
> Hi Edward,
>
> It has just occured to me that the value system returns is the status of
the
> call, not the actual count output of grep, which is written to the
terminal. So
> to be able to access that value should I be able to scanf the output or
> something?
>
> Thanks,
> Tim
>
> Edward wrote:
>
> > Hello Tim,
> >
> > Sure, you could for example issue the following from your C-program to
look
> > for your device DeviceName:
> >
> > #include <stdlib.h>
> > ...
> > x = system("grep -c \'^S:.*DeviceName\' /proc/bus/usb/devices");
> >
> > and check if x >= 1.
> >
> > I don't know if there are any other methods, there might be, and most
likely
> > there are. No doubt the /proc/bus/usb/devices is created by one.
> >
> > Best regards,
> > Edward
> >
> > ----- Original Message -----
> > From: "Tim Arney" <[EMAIL PROTECTED]>
> > To: "Edward" <[EMAIL PROTECTED]>
> > Cc: <[EMAIL PROTECTED]>
> > Sent: Thursday, November 18, 2004 14:57
> > Subject: Re: [Linux-usb-users] Detecting unplugged device
> >
> > > Hi Edward,
> > >
> > > Thanks for your quick reply. So can I execute grep from within a C
> > program? Is
> > > there no way you know of using the usb library directly?
> > >
> > > Cheers,
> > > Tim
> > >
> > > Quoting Edward <[EMAIL PROTECTED]>:
> > >
> > > > Hello Tim,
> > > >
> > > > My best bet would be to grep the /proc/bus/usb/devices file for your
> > > > joystick device.
> > > >
> > > > HTH
> > > > Edward
> > > >
> > > > ----- Original Message -----
> > > > From: "Tim Arney" <[EMAIL PROTECTED]>
> > > > To: <[EMAIL PROTECTED]>
> > > > Sent: Thursday, November 18, 2004 13:51
> > > > Subject: [Linux-usb-users] Detecting unplugged device
> > > >
> > > >
> > > > > Hi all,
> > > > >
> > > > > I've written a C/C++ program for controlling a robot with a USB
> > joystick
> > > > > under linux. For this I'm using the joydev module. Some of our
> > robots
> > > > > are quite large and fast, and a safety concern is with the
joystick
> > > > > being unplugged, then the robot should stop. As it stands, when
the
> > > > > joystick is disconnected the "read" call blocks as though there is
no
> > > > > new data. I could open the joystick port as non-blocking, but
then
> > > > > "read" just returns like there's no new data. What I really need
to
> > be
> > > > > able to do is determine whether the joystick is still attached,
and I
> > > > > figure somewhere along the chain (kernel->usb->input->joystick)
> > someone
> > > > > knows whether it's there, and my best guess would be the linux usb
> > > > > driver. So anyway, I'm essentially looking for a point in the
right
> > > > > direction as to how I might test to see if the joystick is
connected
> > > > > from my C/C++ program?
> > > > >
> > > > > If it helps I'm using Debian Sarge with Linux kernel 2.4.26 on an
i686
> > > > > system.
> > > > >
> > > > > Thanks a lot,
> > > > > Tim
> > > > >
> > > > >
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