将C++与Go链接

huangapple
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英文:

Linking C++ with Go

问题

我正在尝试将C++的OpenCV程序与Go语言绑定。我正在使用来自<https://stackoverflow.com/questions/16747021/how-do-you-statically-link-a-c-library-in-go-using-cgo>的概念。我的myimgcom.cpp文件如下：

  1. /**
  2. * @file SURF_FlannMatcher
  3. * @brief SURF detector + descriptor + FLANN Matcher
  4. * @author A. Huaman
  5.  Edited: nnnnn
  6. */
  8. #include <stdio.h>
  9. #include <string>
  10. #include <iostream>
  11. #include "opencv2/core/core.hpp"
  12. #include "opencv2/features2d/features2d.hpp"
  13. #include "opencv2/highgui/highgui.hpp"
  14. #include "opencv2/nonfree/features2d.hpp"
  16. using namespace cv;
  18. void readme();
  20. int mysurf(int myarg)
  21. {
  23.  string option1 = "./Lenna.png";
  24.  string option2 = "./Lenna.png";
  26.  if (myarg != 3)
  27.  {
  28.      readme();
  29.      return -1;
  30.  }
  32.  std::cout << option1 << option2;
  34.  Mat img_1 = imread(option1, CV_LOAD_IMAGE_GRAYSCALE);
  35.  Mat img_2 = imread(option2, CV_LOAD_IMAGE_GRAYSCALE);
  37.  if (!img_1.data || !img_2.data)
  38.  {
  39.      std::cout << " --(!) Error reading images " << std::endl;
  40.      return -1;
  41.  }
  43.  //-- Step 1: Detect the keypoints using SURF Detector
  44.  int minHessian = 400;
  46.  SurfFeatureDetector detector(minHessian);
  48.  std::vector<KeyPoint> keypoints_1, keypoints_2;
  50.  detector.detect(img_1, keypoints_1);
  51.  detector.detect(img_2, keypoints_2);
  53.  //-- Step 2: Calculate descriptors (feature vectors)
  54.  SurfDescriptorExtractor extractor;
  56.  Mat descriptors_1, descriptors_2;
  58.  extractor.compute(img_1, keypoints_1, descriptors_1);
  59.  extractor.compute(img_2, keypoints_2, descriptors_2);
  61.  //-- Step 3: Matching descriptor vectors using FLANN matcher
  62.  FlannBasedMatcher matcher;
  63.  std::vector<DMatch> matches;
  64.  matcher.match(descriptors_1, descriptors_2, matches);
  66.  double max_dist = 0;
  67.  double min_dist = 100;
  69.  //-- Quick calculation of max and min distances between keypoints
  70.  for (int i = 0; i < descriptors_1.rows; i++)
  71.  {
  72.      double dist = matches[i].distance;
  73.      if (dist < min_dist)
  74.          min_dist = dist;
  75.      if (dist > max_dist)
  76.          max_dist = dist;
  77.  }
  79.  printf("-- Max dist : %f \n", max_dist);
  80.  printf("-- Min dist : %f \n", min_dist);
  82.  std::vector<DMatch> good_matches;
  84.  for (int i = 0; i < descriptors_1.rows; i++)
  85.  {
  86.      if (matches[i].distance <= max(4 * min_dist, 0.02))
  87.      {
  88.          good_matches.push_back(matches[i]);
  89.      }
  90.  }
  92.  //-- Draw only "good" matches
  93.  Mat img_matches;
  94.  drawMatches(img_1, keypoints_1, img_2, keypoints_2,
  95.              good_matches, img_matches, Scalar::all(-1), Scalar::all(-1),
  96.              vector<char>(), DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS);
  98.  //-- Show detected matches
  99.  imshow("Good Matches", img_matches);
  101.  for (int i = 0; i < (int)good_matches.size(); i++)
  102.  {
  103.      printf("-- Good Match [%d] Keypoint 1: %d  -- Keypoint 2: %d  \n", i, good_matches[i].queryIdx, good_matches[i].trainIdx);
  104.  }
  106.  waitKey(0);
  108.  return 0;
  109. }
  111. void readme()
  112. {
  113.  std::cout << " Usage: ./SURF_FlannMatcher <img1> <img2>" << std::endl;
  114. }

接下来，我的头文件myimgcom.h文件如下：

  1. int mysurf(int);
  2. void readme();

接下来，我的imagetest.go文件如下：

  1. package main
  3. import "fmt"
  5. // #include "myimgcom.h"
  6. import "C"
  8. func main() {
  9.  fmt.Printf("Invoking c library...\n")
  10.  C.mysurf(3)
  11. }

我执行以下命令：

  1. gcc -O2 -c myimgcom.cpp -> 成功运行
  2. ar q libgb.a myimgcom.o -> 成功运行
  3. go build imagetest.go -> 这里我得到以下错误：
  4. # command-line-arguments
  5. Undefined symbols for architecture x86_64:
  6. "_mysurf", referenced from:
  7. __cgo_8db0969da00f_Cfunc_mysurf in imagetest.cgo2.o
  8. (maybe you meant: __cgo_8db0969da00f_Cfunc_mysurf)
  9. ld: symbol(s) not found for architecture x86_64
  10. clang: error: linker command failed with exit code 1 (use -v to see invocation)

我认为问题是链接pkg config和cflags与cgo。有人能建议我如何解决这个问题吗？我正在使用Mac OS。

英文:

I am trying to bind C++ OpenCV programs with Go. I am using the concept from <https://stackoverflow.com/questions/16747021/how-do-you-statically-link-a-c-library-in-go-using-cgo>[1]. My myimgcom.cpp file is:

  1. /**
  2. * @file SURF_FlannMatcher
  3. * @brief SURF detector + descriptor + FLANN Matcher
  4. * @author A. Huaman
  5. Edited: nnnnn
  6. */
  7. #include &lt;stdio.h&gt;
  8. #include &lt;string&gt;
  9. #include &lt;iostream&gt;
  10. #include &quot;opencv2/core/core.hpp&quot;
  11. #include &quot;opencv2/features2d/features2d.hpp&quot;
  12. #include &quot;opencv2/highgui/highgui.hpp&quot;
  13. #include &quot;opencv2/nonfree/features2d.hpp&quot;
  14. using namespace cv;
  15. void readme();
  16. int mysurf( int myarg)
  17. {
  18. string option1= &quot;./Lenna.png&quot;;
  19. string option2= &quot;./Lenna.png&quot;;
  20. if( myarg != 3 )
  21. { readme(); return -1; }
  22. std::cout &lt;&lt; option1 &lt;&lt; option2;
  23. Mat img_1 = imread( option1, CV_LOAD_IMAGE_GRAYSCALE );
  24. Mat img_2 = imread( option2, CV_LOAD_IMAGE_GRAYSCALE );
  25. if( !img_1.data || !img_2.data )
  26. { std::cout&lt;&lt; &quot; --(!) Error reading images &quot; &lt;&lt; std::endl; return -1; }
  27. //-- Step 1: Detect the keypoints using SURF Detector
  28. int minHessian = 400;
  29. SurfFeatureDetector detector( minHessian );
  30. std::vector&lt;KeyPoint&gt; keypoints_1, keypoints_2;
  31. detector.detect( img_1, keypoints_1 );
  32. detector.detect( img_2, keypoints_2 );
  33. //-- Step 2: Calculate descriptors (feature vectors)
  34. SurfDescriptorExtractor extractor;
  35. Mat descriptors_1, descriptors_2;
  36. extractor.compute( img_1, keypoints_1, descriptors_1 );
  37. extractor.compute( img_2, keypoints_2, descriptors_2 );
  38. //-- Step 3: Matching descriptor vectors using FLANN matcher
  39. FlannBasedMatcher matcher;
  40. std::vector&lt; DMatch &gt; matches;
  41. matcher.match( descriptors_1, descriptors_2, matches );
  42. double max_dist = 0; double min_dist = 100;
  43. //-- Quick calculation of max and min distances between keypoints
  44. for( int i = 0; i &lt; descriptors_1.rows; i++ )
  45. { double dist = matches[i].distance;
  46. if( dist &lt; min_dist ) min_dist = dist;
  47. if( dist &gt; max_dist ) max_dist = dist;
  48. }
  49. printf(&quot;-- Max dist : %f \n&quot;, max_dist );
  50. printf(&quot;-- Min dist : %f \n&quot;, min_dist );
  51. std::vector&lt; DMatch &gt; good_matches;
  52. for( int i = 0; i &lt; descriptors_1.rows; i++ )
  53. { if( matches[i].distance &lt;= max(4*min_dist, 0.02) )
  54. { good_matches.push_back( matches[i]); }
  55. }
  56. //-- Draw only &quot;good&quot; matches
  57. Mat img_matches;
  58. drawMatches( img_1, keypoints_1, img_2, keypoints_2,
  59. good_matches, img_matches, Scalar::all(-1), Scalar::all(-1),
  60. vector&lt;char&gt;(), DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS );
  61. //-- Show detected matches
  62. imshow( &quot;Good Matches&quot;, img_matches );
  63. for( int i = 0; i &lt; (int)good_matches.size(); i++ )
  64. { printf( &quot;-- Good Match [%d] Keypoint 1: %d  -- Keypoint 2: %d  \n&quot;, i,    good_matches[i].queryIdx, good_matches[i].trainIdx ); }
  65. waitKey(0);
  66. return 0;
  67. }
  68. void readme()
  69. { std::cout &lt;&lt; &quot; Usage: ./SURF_FlannMatcher &lt;img1&gt; &lt;img2&gt;&quot; &lt;&lt; std::endl; }

Next, my header file myimgcom.h file is:

  1. int mysurf( int);
  2. void readme();

Next, my imagetest.go file is:

  1. package main
  2. import &quot;fmt&quot;
  3. // #include &quot;myimgcom.h&quot;
  4. import &quot;C&quot;
  5. func main() {
  6. fmt.Printf(&quot;Invoking c library...\n&quot;)
  7. C.mysurf( 3)
  8. }

I am doing the following commands:

  1.  gcc -O2 -c myimgcom.cpp  -&gt; runs successfully
  2. ar q libgb.a myimgcom.o  -&gt; runs successfully
  3. go build imagetest.go    -&gt; Here I get the following error:
  4. # command-line-arguments
  5. Undefined symbols for architecture x86_64:
  6. &quot;_mysurf&quot;, referenced from:
  7. __cgo_8db0969da00f_Cfunc_mysurf in imagetest.cgo2.o
  8. (maybe you meant: __cgo_8db0969da00f_Cfunc_mysurf)
  9. ld: symbol(s) not found for architecture x86_64
  10. clang: error: linker command failed with exit code 1 (use -v to see invocation)

I think the problem is linking the pkg config and cflags with cgo. Can anybody suggest me how can I solve the issue? I am working with Mac OS.

答案1

得分: 2

C++不是C语言，调用约定也不同。几乎不可能直接调用C++。如果你想从Go语言中调用它，首先需要创建一个C语言的包装器。在你的情况下，通过在函数声明中添加"extern C"应该可以工作。

  1. extern "C"
  2. int mysurf(int myarg)
  3. {
  4.     // 在这里编写代码
  5. }
英文:

C++ isn't C, and call conventions are different. It's almost impossible to call C++ directly. If you want to call it from Go, first do a C wrapper. In your case by adding "extern C" to function declarations should work.

  1. extern &quot;C&quot;
  2. int mysurf(int myarg)
  3. {
  4. // code here
  5. }

huangapple
  • 本文由 发表于 2015年7月17日 20:37:03
  • 转载请务必保留本文链接：https://go.coder-hub.com/31476014.html
  • c++
  • cgo
  • go
  • opencv
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