linker - Error: C++ unresolved external symbol -

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this question has answer here:

i using 2 c files written others in c++ project in visual studio 2008 (actually, provided free online polygon intersection library).

the 2 files downloaded gcp.h , gcp.c. copied gcp.h , gcp.c project directory. linker gave me error:

unresolved external symbol: void __cdecl gpc_polygon_clip(enum gpc_op,struct gpc_polygon *,struct gpc_polygon *,struct gpc_polygon *)

below how wrote code uses library:

static int poly_intersection(convex_polygon& poly1,convex_polygon& poly2,convex_polygon& rp) {     if(!poly1.is_convex() || !poly2.is_convex())         return 1;      // construct 1st convex polygon     gpc_vertex *gvp1 = new gpc_vertex[poly1.size()];     gpc_vertex v1;     (unsigned int n = 0; n < poly1.size(); n++)     {         v1.x = poly1.vertex(n).x();         v1.y = poly1.vertex(n).y();         gvp1[n] = v1;     }      gpc_vertex_list gvl1;     gvl1.num_vertices = poly1.size();     gvl1.vertex = gvp1;      gpc_vertex_list *gvlp1 = new gpc_vertex_list[1];     gvlp1[0] = gvl1;      gpc_polygon gp1;     gp1.num_contours = 1;     gp1.hole = 0;     gp1.contour = gvlp1;      // construct 2st convex polygon     gpc_vertex *gvp2 = new gpc_vertex[poly2.size()];     gpc_vertex v2;     (unsigned int n = 0; n < poly2.size(); n++)     {         v2.x = poly2.vertex(n).x();         v2.y = poly2.vertex(n).y();         gvp2[n] = v2;     }      gpc_vertex_list gvl2;     gvl2.num_vertices = poly2.size();     gvl2.vertex = gvp2;      gpc_vertex_list *gvlp2 = new gpc_vertex_list[1];     gvlp2[0] = gvl2;      gpc_polygon gp2;     gp2.num_contours = 1;     gp2.hole = 0;     gp2.contour = gvlp2;      // convex polygon intersection     gpc_polygon result;     gpc_polygon_clip(gpc_int, &gp1, &gp2, &result);

and clarity, content of 2 files used are

#gcp.h  #define gpc_epsilon (dbl_epsilon) #define gpc_version "2.32"  /* ===========================================================================                            public data types =========================================================================== */  typedef enum                        /* set operation type                */ {   gpc_diff,                         /* difference                        */   gpc_int,                          /* intersection                      */   gpc_xor,                          /* exclusive or                      */   gpc_union                         /* union                             */ } gpc_op;  typedef struct                      /* polygon vertex structure          */ {   double              x;            /* vertex x component                */   double              y;            /* vertex y component                */ } gpc_vertex;  typedef struct                      /* vertex list structure             */ {   int                 num_vertices; /* number of vertices in list        */   gpc_vertex         *vertex;       /* vertex array pointer              */ } gpc_vertex_list;  typedef struct                      /* polygon set structure             */ {   int                 num_contours; /* number of contours in polygon     */   int                *hole;         /* hole / external contour flags     */   gpc_vertex_list    *contour;      /* contour array pointer             */ } gpc_polygon;  typedef struct                      /* tristrip set structure            */ {   int                 num_strips;   /* number of tristrips               */   gpc_vertex_list    *strip;        /* tristrip array pointer            */ } gpc_tristrip;   /* ===========================================================================                        public function prototypes =========================================================================== */  void gpc_read_polygon        (file            *infile_ptr,                               int              read_hole_flags,                               gpc_polygon     *polygon);  void gpc_write_polygon       (file            *outfile_ptr,                               int              write_hole_flags,                               gpc_polygon     *polygon);  void gpc_add_contour         (gpc_polygon     *polygon,                               gpc_vertex_list *contour,                               int              hole);  void gpc_polygon_clip        (gpc_op           set_operation,                               gpc_polygon     *subject_polygon,                               gpc_polygon     *clip_polygon,                               gpc_polygon     *result_polygon);  void gpc_tristrip_clip       (gpc_op           set_operation,                               gpc_polygon     *subject_polygon,                               gpc_polygon     *clip_polygon,                               gpc_tristrip    *result_tristrip);  void gpc_polygon_to_tristrip (gpc_polygon     *polygon,                               gpc_tristrip    *tristrip);  void gpc_free_polygon        (gpc_polygon     *polygon);  void gpc_free_tristrip       (gpc_tristrip    *tristrip);  #endif

before own method @ beginning of c++ header file, put #include "gpc.h", thought take care of it. didn't work.

this file structure of project

if use c function in .cpp file, include c header file below:

extern "c" {     #include "gpc.h" }

because function symbol in c , c++ different.


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