how to read data from /dev/video0

[jody]

Hi
I have an Acer Laptop with a built-in Crystal Eye webcam
which works (tested it with luvcview).
The camera is represented by /dev/video0.

I would like to read data from this device, but i don't manage to do it.
This code

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>

int main(int iArgC, char *apArgV[]) {
    char *buf[76800]; // camera resolution 320x240
    int iErr = 0;

    int fd = open("/dev/video0", O_RDONLY);
    if (fd >= 0) {
        printf("fd is %d\n", fd);
        
        ssize_t num=read(fd, buf, 76800);
        
        if (num > 0) {
            printf("Read %d bytes\n", num);
        } else {
            iErr = errno;
            printf("Coudn't read - error %d:[%s]\n", iErr, strerror(iErr));
        }
        close(fd);
    } else {
        iErr = errno;
        printf("Couldn't open - error %d:[%s]\n", iErr, strerror(iErr));
    }
    return iErr;

}

will successfully open the device (filedescriptor fd is 3), but the
subsequent call to "read" returns errno 19 ("No such device"),
even though it exists. Same happens if i have luvcview working
at the same time.

Also, the call 'cat /dev/video0' returns "No such device":

jody@enki ~ $ ls -l /dev/video0
crw-rw----+ 1 root video 81, 0 Jul 17 00:09 /dev/video0
jody@enki ~ $ cat /dev/video0
cat: /dev/video0: No such device

(BTW: i am member of the group 'video',
but i also get the same error if i do this as 'root')

Can anybody give me some pointers how i can open the device,
get som data from it and close it again?

Thank You
Jody

[Rubberman]

You probably need to open it for read+write access and then send some sort of command (probably an ioctl() call) to enable it.

[jody]

HI Rubberman

You are right.
The V4L2 API documentation
describes all the required ioctl-commands and also has example code.

Jody

[Rubberman]

Kewl! Glad you got that sorted out. Sometimes all one needs is a nudge in the right direction. Like the old parable, if you give a person a fish, they are fed for a day. If you teach them how to fish, they will never go hungry (unless they live on the Gulf of Mexico).