Cocos2dAttachmentLoader needs to be C++.

spine-cocos2dx/3/example/proj.win32/spine-cocos2dx.vcxproj

@@ -145,7 +145,7 @@
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="..\..\src\spine\AttachmentVertices.cpp" />
-    <ClCompile Include="..\..\src\spine\Cocos2dAttachmentLoader.c" />
+    <ClCompile Include="..\..\src\spine\Cocos2dAttachmentLoader.cpp" />
     <ClCompile Include="..\..\src\spine\SkeletonBatch.cpp" />
     <ClCompile Include="..\..\src\spine\SkeletonAnimation.cpp" />
     <ClCompile Include="..\..\src\spine\SkeletonRenderer.cpp" />

spine-cocos2dx/3/example/proj.win32/spine-cocos2dx.vcxproj.filters

@@ -83,10 +83,10 @@
     <ClCompile Include="..\..\src\spine\SkeletonBatch.cpp">
       <Filter>src</Filter>
     </ClCompile>
-    <ClCompile Include="..\..\src\spine\Cocos2dAttachmentLoader.c">
+    <ClCompile Include="..\..\src\spine\AttachmentVertices.cpp">
       <Filter>src</Filter>
     </ClCompile>
-    <ClCompile Include="..\..\src\spine\AttachmentVertices.cpp">
+    <ClCompile Include="..\..\src\spine\Cocos2dAttachmentLoader.cpp">
       <Filter>src</Filter>
     </ClCompile>
   </ItemGroup>

spine-cocos2dx/3/src/spine/Cocos2dAttachmentLoader.h

@@ -34,9 +34,7 @@
 
 #include <spine/AtlasAttachmentLoader.h>
 
-#ifdef __cplusplus
 extern "C" {
-#endif
 
 typedef struct Cocos2dAttachmentLoader {
 	spAttachmentLoader super;
@@ -45,8 +43,6 @@ typedef struct Cocos2dAttachmentLoader {
 
 Cocos2dAttachmentLoader* Cocos2dAttachmentLoader_create (spAtlas* atlas);
 
-#ifdef __cplusplus
 }
-#endif
 
 #endif /* SPINE_COCOS2DATTACHMENTLOADER_H_ */