OpenCV cannot find video device

Question

I cannot use webcam as input device for OpenCV 2.3.1 in Ubuntu 11.04, this code works fine on windows:

#include "cv.h"
#include "highgui.h"
#include <stdio.h>

// A Simple Camera Capture Framework
int main() {

  CvCapture* capture = cvCaptureFromCAM(-1);
  if( !capture ) {
    fprintf( stderr, "ERROR: capture is NULL \n" );
    getchar();
    return -1;
  }

  // Create a window in which the captured images will be presented
  cvNamedWindow( "mywindow", CV_WINDOW_AUTOSIZE );

  // Show the image captured from the camera in the window and repeat
  while( 1 ) {

    // Get one frame
    IplImage* frame = cvQueryFrame( capture );
    if( !frame ) {
      fprintf( stderr, "ERROR: frame is null...\n" );
      getchar();
      break;
    }

    cvShowImage( "mywindow", frame );
    // Do not release the frame!

    //If ESC key pressed, Key=0x10001B under OpenCV 0.9.7(linux version),
    //remove higher bits using AND operator
    if( (cvWaitKey(10) & 255) == 27 ) break;
  }

  // Release the capture device housekeeping
  cvReleaseCapture( &capture );
  cvDestroyWindow( "mywindow" );
  return 0;
}

It returns "ERROR: capture is NULL "

Answer 1

I found the solution, I need to install libv4l-0 and libv4l-dev then compile OpenCV with USE_V4L=ON.