Have been using Cmake configured opencv_contrib - 4.1.0, but in the use of SIFT algorithm error will appear when "cannot resolve the external command"

 
#include  
#include  
#include  
#include  
#include  
//# include & lt; Opencv2 xfeatures2d/nonfree. Hpp>//OpenCV 4.2.0 and later 
Using the namespace CV: : xfeatures2d; 
Using the namespace CV; 
using namespace std; 
Int main () 
{
CV: : Mat imageL=CV: : imread (" imgL. BMP "); 
CV: : Mat imageR=CV: : imread (" imgR. BMP "); 


//method to extract the feature points 
//SIFT 
//CV: : Ptr Sift=CV: : xfeatures2d: : sift: : create (); 
//CV: : Ptr Sift=CV: : sift: : Creat ();//OpenCV 4.4.0 and later 
//the ORB 
//CV: : Ptr The orb=CV: : the orb: : create (); 
//SURF 
CV: : Ptr Surf=CV: : xfeatures2d: : surf: : create (); 

//feature point 
STD: : vector KeyPointL keyPointR; 
//to extract the feature points alone 
Surf - & gt; Detect (imageL keyPointL); 
Surf - & gt; Detect (imageR, keyPointR); 

//draw feature point 
CV: : Mat keyPointImageL; 
CV: : Mat keyPointImageR; 
DrawKeypoints (imageL, keyPointL keyPointImageL, CV: : Scalar: : (1), all CV: : DrawMatchesFlags: : DRAW_RICH_KEYPOINTS); 
DrawKeypoints (imageR, keyPointR keyPointImageR, CV: : Scalar: : (1), all CV: : DrawMatchesFlags: : DRAW_RICH_KEYPOINTS); 

//display window 
CV: : namedWindow (" KeyPoints of imageL "); 
CV: : namedWindow (" KeyPoints of the imageR "); 

//display feature point 
CV: : imshow (" KeyPoints of imageL keyPointImageL); 
CV: : imshow (" KeyPoints of the imageR, "keyPointImageR); 

//feature point matching 
CV: : Mat despL despR; 
//to extract the feature points and calculate the feature descriptor 
Surf - & gt; DetectAndCompute (imageL, CV: : Mat (), keyPointL, despL); 
Surf - & gt; DetectAndCompute (imageR, CV: : Mat (), keyPointR, despR); 

//Struct for DMatch: query descriptor index, "train" descriptor index, train the image index and short between descriptors. 
//int queryIdx - & gt; Is to test the image feature points subscript descriptor (descriptor), as well as corresponding feature point (keypoint descriptors of the subscript, 
//int trainIdx - & gt; Is a sample image feature point descriptor subscript, is also the corresponding feature points subscript, 
//int imgIdx - & gt; Useful when the sample is more images, 
//float short - & gt; On behalf of the pair of matching feature points descriptor (essence is a vector) of Euclidean distance, the smaller the value also means that, the more similar two feature points, 
STD: : vector Matches; 

//if the flannBased method so desp through orb to different need to convert the type of type 
If (despL. Type ()!=CV_32F | | despR. Type ()!=CV_32F) 
{
DespL. ConvertTo (despL CV_32F); 
DespR. ConvertTo (despR CV_32F); 
} 

CV: : Ptr The matcher=CV: : DescriptorMatcher: : create (" FlannBased "); 
The matcher - & gt; Match (despL despR, matches); 

//calculate the maximum distance between the feature points 
Double maxDist=0; 
For (int I=0; I & lt; DespL. Rows; I++) 
{
Double dist=matches [I]. Short; 
If (dist & gt; MaxDist) 
MaxDist=dist. 
} 

//select good matching point 
STD: : vectorFor (int I=0; I & lt; DespL. Rows; I++) 
{
If (matches [I] short & lt; 0.5 * maxDist) 
{
Good_matches. Push_back (matches [I]); 
} 
} 



CV: : Mat imageOutput; 
CV: : drawMatches (imageL keyPointL, imageR, keyPointR, good_matches, imageOutput); 

CV: : namedWindow (" picture of matching "); 
CV: : imshow (" picture of matching, "imageOutput); 
CV: : waitKey (0); 
return 0; 
} 

Don't know is what reason, so no problem,,,,,,,,,