Linking C++ with Go

Question

我正在尝试将c++ OpenCV程序与Go绑定。我使用的概念从你如何静态链接一个c库在go使用cgo?[1]。我的myimgcom.cpp文件是:

/**
* @file SURF_FlannMatcher
* @brief SURF detector + descriptor + FLANN Matcher
* @author A. Huaman
 Edited: nnnnn
*/
#include <stdio.h>
#include <string>
#include <iostream>
#include "opencv2/core/core.hpp"
#include "opencv2/features2d/features2d.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/nonfree/features2d.hpp"
using namespace cv;
void readme();
int mysurf( int myarg)
{
 string option1= "./Lenna.png";
 string option2= "./Lenna.png";
 if( myarg != 3 )
 { readme(); return -1; }
 std::cout << option1 << option2;
 Mat img_1 = imread( option1, CV_LOAD_IMAGE_GRAYSCALE );
 Mat img_2 = imread( option2, CV_LOAD_IMAGE_GRAYSCALE );
 if( !img_1.data || !img_2.data )
 { std::cout<< " --(!) Error reading images " << std::endl; return -1; }
 //-- Step 1: Detect the keypoints using SURF Detector
 int minHessian = 400;
 SurfFeatureDetector detector( minHessian );
 std::vector<KeyPoint> keypoints_1, keypoints_2;
 detector.detect( img_1, keypoints_1 );
 detector.detect( img_2, keypoints_2 );
 //-- Step 2: Calculate descriptors (feature vectors)
 SurfDescriptorExtractor extractor;
 Mat descriptors_1, descriptors_2;
 extractor.compute( img_1, keypoints_1, descriptors_1 );
 extractor.compute( img_2, keypoints_2, descriptors_2 );
 //-- Step 3: Matching descriptor vectors using FLANN matcher
 FlannBasedMatcher matcher;
 std::vector< DMatch > matches;
 matcher.match( descriptors_1, descriptors_2, matches );
 double max_dist = 0; double min_dist = 100;
 //-- Quick calculation of max and min distances between keypoints
 for( int i = 0; i < descriptors_1.rows; i++ )
 { double dist = matches[i].distance;
    if( dist < min_dist ) min_dist = dist;
    if( dist > max_dist ) max_dist = dist;
 }
  printf("-- Max dist : %f n", max_dist );
  printf("-- Min dist : %f n", min_dist );
  std::vector< DMatch > good_matches;
  for( int i = 0; i < descriptors_1.rows; i++ )
  { if( matches[i].distance <= max(4*min_dist, 0.02) )
  { good_matches.push_back( matches[i]); }
  }
  //-- Draw only "good" matches
  Mat img_matches;
  drawMatches( img_1, keypoints_1, img_2, keypoints_2,
           good_matches, img_matches, Scalar::all(-1), Scalar::all(-1),
           vector<char>(), DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS );
  //-- Show detected matches
  imshow( "Good Matches", img_matches );
   for( int i = 0; i < (int)good_matches.size(); i++ )
  { printf( "-- Good Match [%d] Keypoint 1: %d  -- Keypoint 2: %d  n", i,    good_matches[i].queryIdx, good_matches[i].trainIdx ); }
  waitKey(0);
  return 0;
 }

 void readme()
 { std::cout << " Usage: ./SURF_FlannMatcher <img1> <img2>" << std::endl; }

接下来，我的头文件myimgcom.h文件是:

int mysurf( int);
void readme();

接下来，我的imagetest.go文件是:

package main
import "fmt"
// #include "myimgcom.h"
import "C"
func main() {
  fmt.Printf("Invoking c library...n")
  C.mysurf( 3)
}

我正在执行以下命令:

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

我认为问题是链接pkg配置和cflags与go。谁能告诉我怎么解决这个问题?我用的是Mac OS

Answer 1

c++不是C，调用约定也不同。直接调用c++几乎是不可能的。如果你想从Go调用它，首先做一个C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。

extern "C"
int mysurf(int myarg)
{
 // code here
}