Didn't understand these unresolved externals?

Code:

#ifndef _CORRIDOR_H_

#define _CORRIDOR_H_



#include <math.h>

#include <vector>

#include <algorithm>

#include "Recast.h"

#include "RecastAlloc.h"

#include "RecastAssert.h"





/////////////////////////////



int getCornerHeight(int x, int y, int i, int dir,

                                                   const rcCompactHeightfield& chf,

                                                   bool& isBorderVertex);



void simplifyContour(rcIntArray& points, rcIntArray& simplified,

                                                        const float maxError, const int maxEdgeLen, const int buildFlags);



void removeDegenerateSegments(rcIntArray& simplified);



int calcAreaOfPolygon2D(const int* verts, const int nverts);



void getClosestIndices(const int* vertsa, const int nvertsa,

                                                          const int* vertsb, const int nvertsb,

                                                          int& ia, int& ib);



bool mergeContours(rcContour& ca, rcContour& cb, int ia, int ib);



void znWalkContour(int x, int y, int i, rcCompactHeightfield& chf, unsigned char* flags, rcIntArray& points);

Code:

static void simplifyContour(rcIntArray& points, rcIntArray& simplified,

                                                        const float maxError, const int maxEdgeLen, const int buildFlags)

{

....

Code:

1>Corridor.obj : error LNK2019: unresolved external symbol "bool __cdecl mergeContours(struct rcContour &,struct rcContour &,int,int)" (?mergeContours@@YA_NAAUrcContour@@0HH@Z) referenced in function "bool __cdecl znBuildContours(class rcContext *,struct rcCompactHeightfield &,float,int,struct rcContourSet &,int)" (?znBuildContours@@YA_NPAVrcContext@@AAUrcCompactHeightfield@@MHAAUrcContourSet@@H@Z)

1>Corridor.obj : error LNK2019: unresolved external symbol "void __cdecl getClosestIndices(int const *,int,int const *,int,int &,int &)" (?getClosestIndices@@YAXPBHH0HAAH1@Z) referenced in function "bool __cdecl znBuildContours(class rcContext *,struct rcCompactHeightfield &,float,int,struct rcContourSet &,int)" (?znBuildContours@@YA_NPAVrcContext@@AAUrcCompactHeightfield@@MHAAUrcContourSet@@H@Z)

1>Corridor.obj : error LNK2019: unresolved external symbol "int __cdecl calcAreaOfPolygon2D(int const *,int)" (?calcAreaOfPolygon2D@@YAHPBHH@Z) referenced in function "bool __cdecl znBuildContours(class rcContext *,struct rcCompactHeightfield &,float,int,struct rcContourSet &,int)" (?znBuildContours@@YA_NPAVrcContext@@AAUrcCompactHeightfield@@MHAAUrcContourSet@@H@Z)

1>Corridor.obj : error LNK2019: unresolved external symbol "void __cdecl removeDegenerateSegments(class rcIntArray &)" (?removeDegenerateSegments@@YAXAAVrcIntArray@@@Z) referenced in function "bool __cdecl znBuildContours(class rcContext *,struct rcCompactHeightfield &,float,int,struct rcContourSet &,int)" (?znBuildContours@@YA_NPAVrcContext@@AAUrcCompactHeightfield@@MHAAUrcContourSet@@H@Z)

1>Corridor.obj : error LNK2019: unresolved external symbol "void __cdecl simplifyContour(class rcIntArray &,class rcIntArray &,float,int,int)" (?simplifyContour@@YAXAAVrcIntArray@@0MHH@Z) referenced in function "bool __cdecl znBuildContours(class rcContext *,struct rcCompactHeightfield &,float,int,struct rcContourSet &,int)" (?znBuildContours@@YA_NPAVrcContext@@AAUrcCompactHeightfield@@MHAAUrcContourSet@@H@Z)

1>Corridor.obj : error LNK2019: unresolved external symbol "int __cdecl getCornerHeight(int,int,int,int,struct rcCompactHeightfield const &,bool &)" (?getCornerHeight@@YAHHHHHABUrcCompactHeightfield@@AA_N@Z) referenced in function "void __cdecl znWalkContour(int,int,int,struct rcCompactHeightfield &,unsigned char *,class rcIntArray &)" (?znWalkContour@@YAXHHHAAUrcCompactHeightfield@@PAEAAVrcIntArray@@@Z)

1>bin\Debug\\PerfectSim.exe : fatal error LNK1120: 6 unresolved externals

I have include a prototype in an include file. These link time errors still happen.
They are defined as static global functions.
Can't understand it.
Thanks
Jack