How to use the OTSU Threshold in opencv?

Following line makes otsu thresholding operation:

cv::threshold(im_gray, img_bw, 0, 255, CV_THRESH_BINARY | CV_THRESH_OTSU);

• im_gray is a source 8-bit image,
• img_bw is a result,
• 0 means threshold level which actually is omitted because we used CV_THRESH_OTSU flag,
• 255 is a value that is going to be assigned to respectively pixels in the result (namely, to all pixels which value in the source is greater then computed threshold level)
• CV_THRESH_BINARY | CV_THRESH_OTSU is a required flag to perform Otsu thresholding. Because in fact we would like to perform binary thresholding, so we use CV_THRESH_BINARY (you can use any of 5 flags opencv provides) combined with CV_THRESH_OTSU

Link to documentation: http://docs.opencv.org/modules/imgproc/doc/miscellaneous_transformations.html#threshold

In python it is simple

import cv2

img = cv2.imread('img.jpg',0)  #pass 0 to convert into gray level 
ret,thr = cv2.threshold(img, 0, 255, cv2.THRESH_OTSU)
cv2.imshow('win1', thr)
cv2.waitKey(0)  
cv2.destroyAllWindows()