OpenCV: where can i find CV_WINDOW_AUTOSIZE constants?

OpenCV: where can i find CV_WINDOW_AUTOSIZE constants?

I try build sample program in documentation of OpenCV,but i have problem:
error: 'CV_WINDOW_AUTOSIZE' was not declared in this scope
Source of programm:
#include <stdio.h>
#include <opencv2/opencv.hpp>
using namespace cv;
int main( int argc, char** argv )
{
Mat image;
image = imread( argv[1], 1 );
if( argc != 2 || !image.data )
{
printf( "No image data \n" );
return -1;
}
namedWindow( "Display Image", CV_WINDOW_AUTOSIZE );
imshow( "Display Image", image );
waitKey(0);
return 0;
}
I think that CV_WINDOW_AUTOSIZE constants has been contained in certain
header file,but i can't find necessary header file.