链接时出现一个undefined reference to 问题，实在不懂为什么

_Genesis

额。这个问题我实在没搞明白是怎么回事。
先是报错如下：

1. 
   
2. || g++ -o main ex1.o header.o utils.o imgfeatures.o sift.o main.o -I. -I/home/web/include/opencv -L/home/web/lib -lm -lopencv_core -lopencv_ml -lopencv_highgui  -B/home/web/lib
   
3. || main.o: In function `main':
   
4. || main.cpp:(.text+0x85): undefined reference to `sift_features(_IplImage*, feature**)'
   
5. || main.cpp:(.text+0x9d): undefined reference to `sift_features(_IplImage*, feature**)'
   
6. || main.cpp:(.text+0xb5): undefined reference to `stack_imgs1(_IplImage*, _IplImage*)'
   
7. || collect2: ld returned 1 exit status
   
8. || make: *** [main] 错误 1
   

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看提示，是没有sift_features(_IplImage*, feature**)这个函数
下面是代码。
====main.cpp====

1. 
   
2. #include "header.h"
   
3. #include "main.h"
   
4. #include "sift.h"
   
5. #include "utils.h"
   
6. int main(int argc,char* argv[]){
   
7.         printf("hello OPENCV!!!\n========\n");
   
8.         IplImage* img1;
   
9.         IplImage* img2;
   
10.         IplImage* stacked;
    
11.         img1 = cvLoadImage(argv[1],1);
    
12.         img2 = cvLoadImage(argv[2],1);
    
13.         _showImg(img1,"img1");
    
14.         _showImg(img2,"img2");
    
15.         struct feature* ft1,*ft2,*ft;
    
16.         int n1, n2;
    
17.         n1 = sift_features(img1,&ft1);
    
18.         n2 = sift_features(img2,&ft2);
    
19.         stacked = stack_imgs1(img1,img2);
    
20.         _showImg(stacked,"stacked");
    
21. }
    

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==== sift.h ====

1. 
   
2. /*#ifndef SIFT_H*/
   
3. /*#define SIFT_H*/
   
4. #include "cxcore.h"
   
5. /******************************** Structures *********************************/
   
6. /** holds feature data relevant to detection */
   
7. struct detection_data
   
8. {
   
9.         int r;
   
10.         int c;
    
11.         int octv;
    
12.         int intvl;
    
13.         double subintvl;
    
14.         double scl_octv;
    
15. };
    
16. 
    
17. struct feature;
    
18. /******************************* Defs and macros *****************************/
    
19. /** default number of sampled intervals per octave */
    
20. #define SIFT_INTVLS 3
    
21. /** default sigma for initial gaussian smoothing */
    
22. #define SIFT_SIGMA 1.6
    
23. /** default threshold on keypoint contrast |D(x)| */
    
24. #define SIFT_CONTR_THR 0.04
    
25. /** default threshold on keypoint ratio of principle curvatures */
    
26. #define SIFT_CURV_THR 10
    
27. /** double image size before pyramid construction? */
    
28. #define SIFT_IMG_DBL 0
    
29. /** default width of descriptor histogram array */
    
30. #define SIFT_DESCR_WIDTH 4
    
31. /** default number of bins per histogram in descriptor array */
    
32. #define SIFT_DESCR_HIST_BINS 8
    
33. /* assumed gaussian blur for input image */
    
34. #define SIFT_INIT_SIGMA 0.5
    
35. /* width of border in which to ignore keypoints */
    
36. #define SIFT_IMG_BORDER 5
    
37. /* maximum steps of keypoint interpolation before failure */
    
38. #define SIFT_MAX_INTERP_STEPS 5
    
39. /* default number of bins in histogram for orientation assignment */
    
40. #define SIFT_ORI_HIST_BINS 36
    
41. /* determines gaussian sigma for orientation assignment */
    
42. #define SIFT_ORI_SIG_FCTR 1.5
    
43. /* determines the radius of the region used in orientation assignment */
    
44. #define SIFT_ORI_RADIUS 3.0 * SIFT_ORI_SIG_FCTR
    
45. /* number of passes of orientation histogram smoothing */
    
46. #define SIFT_ORI_SMOOTH_PASSES 2
    
47. /* orientation magnitude relative to max that results in new feature */
    
48. #define SIFT_ORI_PEAK_RATIO 0.8
    
49. /* determines the size of a single descriptor orientation histogram */
    
50. #define SIFT_DESCR_SCL_FCTR 3.0
    
51. /* threshold on magnitude of elements of descriptor vector */
    
52. #define SIFT_DESCR_MAG_THR 0.2
    
53. /* factor used to convert floating-point descriptor to unsigned char */
    
54. #define SIFT_INT_DESCR_FCTR 512.0
    
55. /* returns a feature's detection data */
    
56. #define feat_detection_data(f) ( (struct detection_data*)(f->feature_data) )
    
57. /*************************** Function Prototypes *****************************/
    
58. extern int sift_features( IplImage* img, struct feature** feat );
    
59. extern int _sift_features( IplImage* img, struct feature** feat, int intvls,
    
60.                                                   double sigma, double contr_thr, int curv_thr,
    
61.                                                   int img_dbl, int descr_width, int descr_hist_bins );
    
62. /*#endif*/
    

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==== sift.c====

1. 
   
2. #include "sift.h"
   
3. #include "imgfeatures.h"
   
4. #include "utils.h"
   
5. 
   
6. #include <cxcore.h>
   
7. #include <cv.h>
   
8. 
   
9. /************************* Local Function Prototypes *************************/
   
10. 
    
11. IplImage* create_init_img( IplImage*, int, double );
    
12. IplImage* convert_to_gray32( IplImage* );
    
13. IplImage*** build_gauss_pyr( IplImage*, int, int, double );
    
14. IplImage* downsample( IplImage* );
    
15. IplImage*** build_dog_pyr( IplImage***, int, int );
    
16. CvSeq* scale_space_extrema( IplImage***, int, int, double, int, CvMemStorage*);
    
17. int is_extremum( IplImage***, int, int, int, int );
    
18. struct feature* interp_extremum( IplImage***, int, int, int, int, int, double);
    
19. void interp_step( IplImage***, int, int, int, int, double*, double*, double* );
    
20. CvMat* deriv_3D( IplImage***, int, int, int, int );
    
21. CvMat* hessian_3D( IplImage***, int, int, int, int );
    
22. double interp_contr( IplImage***, int, int, int, int, double, double, double );
    
23. struct feature* new_feature( void );
    
24. int is_too_edge_like( IplImage*, int, int, int );
    
25. void calc_feature_scales( CvSeq*, double, int );
    
26. void adjust_for_img_dbl( CvSeq* );
    
27. void calc_feature_oris( CvSeq*, IplImage*** );
    
28. double* ori_hist( IplImage*, int, int, int, int, double );
    
29. int calc_grad_mag_ori( IplImage*, int, int, double*, double* );
    
30. void smooth_ori_hist( double*, int );
    
31. double dominant_ori( double*, int );
    
32. void add_good_ori_features( CvSeq*, double*, int, double, struct feature* );
    
33. struct feature* clone_feature( struct feature* );
    
34. void compute_descriptors( CvSeq*, IplImage***, int, int );
    
35. double*** descr_hist( IplImage*, int, int, double, double, int, int );
    
36. void interp_hist_entry( double***, double, double, double, double, int, int);
    
37. void hist_to_descr( double***, int, int, struct feature* );
    
38. void normalize_descr( struct feature* );
    
39. int feature_cmp( void*, void*, void* );
    
40. void release_descr_hist( double****, int );
    
41. void release_pyr( IplImage****, int, int );
    
42. 
    
43. 
    
44. /*********************** Functions prototyped in sift.h **********************/
    
45. 
    
46. int sift_features( IplImage* img, struct feature** feat )
    
47. {
    
48.         return _sift_features( img, feat, SIFT_INTVLS, SIFT_SIGMA, SIFT_CONTR_THR,
    
49.                                                         SIFT_CURV_THR, SIFT_IMG_DBL, SIFT_DESCR_WIDTH,
    
50.                                                         SIFT_DESCR_HIST_BINS );
    
51. }
    
52. 
    
53. int _sift_features( IplImage* img, struct feature** feat, int intvls,
    
54.                                    double sigma, double contr_thr, int curv_thr,
    
55.                                    int img_dbl, int descr_width, int descr_hist_bins )
    
56. {
    
57.         IplImage* init_img;
    
58.         IplImage*** gauss_pyr, *** dog_pyr;
    
59.         CvMemStorage* storage;
    
60.         CvSeq* features;
    
61.         int octvs, i, n = 0;
    
62. 
    
63.         /* check arguments */
    
64.         if( ! img )
    
65.                 fatal_error( "NULL pointer error, %s, line %d",  __FILE__, __LINE__ );
    
66. 
    
67.         if( ! feat )
    
68.                 fatal_error( "NULL pointer error, %s, line %d",  __FILE__, __LINE__ );
    
69. 
    
70.         /* build scale space pyramid; smallest dimension of top level is ~4 pixels */
    
71.         init_img = create_init_img( img, img_dbl, sigma );
    
72.         octvs = log( MIN( init_img->width, init_img->height ) ) / log(2) - 2;
    
73.         gauss_pyr = build_gauss_pyr( init_img, octvs, intvls, sigma );
    
74.         dog_pyr = build_dog_pyr( gauss_pyr, octvs, intvls );
    
75. 
    
76.         storage = cvCreateMemStorage( 0 );
    
77.         features = scale_space_extrema( dog_pyr, octvs, intvls, contr_thr,
    
78.                 curv_thr, storage );
    
79.         calc_feature_scales( features, sigma, intvls );
    
80.         if( img_dbl )
    
81.                 adjust_for_img_dbl( features );
    
82.         calc_feature_oris( features, gauss_pyr );
    
83.         compute_descriptors( features, gauss_pyr, descr_width, descr_hist_bins );
    
84. 
    
85.         /* sort features by decreasing scale and move from CvSeq to array */
    
86.         cvSeqSort( features, (CvCmpFunc)feature_cmp, NULL );
    
87.         n = features->total;
    
88.         *feat = calloc( n, sizeof(struct feature) );
    
89.         *feat = cvCvtSeqToArray( features, *feat, CV_WHOLE_SEQ );
    
90.         for( i = 0; i < n; i++ )
    
91.         {
    
92.                 free( (*feat)[i].feature_data );
    
93.                 (*feat)[i].feature_data = NULL;
    
94.         }
    
95. 
    
96.         cvReleaseMemStorage( &storage );
    
97.         cvReleaseImage( &init_img );
    
98.         release_pyr( &gauss_pyr, octvs, intvls + 3 );
    
99.         release_pyr( &dog_pyr, octvs, intvls + 2 );
    
100.         return n;
     
101. }
     
102. 
     
103. ...... 后面省略，应该没有问题吧
     

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==== Makefile ====

1. 
   
2. CC = g++
   
3. C_ = gcc
   
4. CFLAGS = -c -Wall
   
5. COM_H = header.h
   
6. Objs =  ex1.o header.o utils.o imgfeatures.o sift.o main.o
   
7. CVs = -I. -I/home/web/include/opencv -L/home/web/lib -lm -lopencv_core -lopencv_ml -lopencv_highgui
   
8. 
   
9. main: $(Objs)
   
10.         $(CC) -o main $(Objs) $(CVs) -B/home/web/lib
    
11. 
    
12. header.o: header.cpp header.h
    
13.         $(CC) $(CFLAGS) -o header.o header.cpp $(CVs) -B/home/web/lib
    
14. 
    
15. ex1.o: ex1.cpp ex1.h $(COM_H)
    
16.         $(CC) $(CFLAGS) -o ex1.o ex1.cpp $(CVs) -B/home/web/lib
    
17. 
    
18. utils.o:utils.c
    
19.         $(C_) $(CFLAGS) -o utils.o utils.c $(CVs) -B/home/web/lib
    
20. 
    
21. imgfeatures.o:imgfeatures.c utils.c
    
22.         $(C_) $(CFLAGS) -o imgfeatures.o imgfeatures.c $(CVs) -B/home/web/lib
    
23. 
    
24. sift.o:sift.c utils.c imgfeatures.c
    
25.         $(C_) $(CFLAGS) -o sift.o sift.c $(CVs) -B/home/web/lib
    
26. 
    
27. main.o: main.cpp main.h $(COM_H)
    
28.         $(CC) $(CFLAGS) -o main.o main.cpp $(CVs) -B/home/web/lib
    
29. 
    
30. clean:
    
31.         rm main $(Objs)
    

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然后是这个：

1. 
   
2. web@pc-laptop:~/workTree/panorama/SIFT$ strings sift.o | grep feature
   
3. sizeof(((features))->first[0]) == sizeof(CvSeqBlock) && ((features))->elem_size == sizeof(struct feature)
   
4. calc_feature_scales
   

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crazyhadoop

undefined reference to 没有找到这几个函数定义的地方。。。


ps：能把代码括起来吗？

_Genesis

使用[code][/code]阔气来把？已经括了。实在不好意思，忘记了。

确实是 reference to 的问题。但是，我觉得，没有问题啊，在link需要的函数，在sift.c里面，sift.h 里面声明了extern 函数XXX 。为什么main.c里面还是 reference to的问题呢？

king318hua

楼主解决了问题吗？我也碰到这个情况，，，刚开始项目编译都没什么问题的，，但有时候编译就出现的这样的问题，，不知道怎么弄，

king318hua

我的qq413841175 交流

comealong

extern "C" {
#include "sift.h"
}

5wuxiaohua

在c++的文件中编译.c文件，要在.c对应的.h文件中加上
#ifdef __cplusplus
extern "C"
{
#endif

函数声明

#ifdef __cplusplus
}
#endif