Exporting functions from a DLL with dllexport

Question

I d like a simple example of exporting a function from a C   Windows DLL   I d like to see the header  the  cpp file  and the  def file  if absolutely required    I d like the exported name to be undecorated  I d like to use the most standard calling convention    stdcall    I d like the use   declspec dllexport  and not have to use a  def file   For example       header   extern  C           declspec dllexport  int   stdcall foo long bar            cpp   int   stdcall foo long bar          return 0        I m trying to avoid the linker added underscores and or numbers  byte counts   to the name    I m OK with not supporting dllimport and dllexport using the same header  I don t want any information about exporting C   class methods  just c-style global functions   UPDATE  Not including the calling convention  and using extern  C   gives me the export names as I like  but what does that mean  Is whatever default calling convention I m getting what pinvoke   NET   declare  vb6   and GetProcAddress would expect   I guess for GetProcAddress it would depend on the function pointer the caller created    I want this DLL to be used without a header file  so I don t really need the a lot of the fancy  defines to make the header usable by a caller   I m OK with an answer being that I have to use a   def file

User · Accepted Answer

If you want plain C exports  use a C project not C    C   DLLs rely on name-mangling for all the C  isms  namespaces etc      You can compile your code as C by going into your project settings under C C  - gt Advanced  there is an option  quot Compile As quot  which corresponds to the compiler switches  TP and  TC  If you still want to use C   to write the internals of your lib but export some functions unmangled for use outside C    see the second section below  Exporting Importing DLL Libs in VC   What you really want to do is define a conditional macro in a header that will be included in all of the source files in your DLL project   ifdef LIBRARY EXPORTS      define LIBRARY API   declspec dllexport   else      define LIBRARY API   declspec dllimport   endif  Then on a function that you want to be exported you use LIBRARY API  LIBRARY API int GetCoolInteger     In your library build project create a define LIBRARY EXPORTS this will cause your functions to be exported for your DLL build  Since LIBRARY EXPORTS will not be defined in a project consuming the DLL  when that project includes the header file of your library all of the functions will be imported instead  If your library is to be cross-platform you can define LIBRARY API as nothing when not on Windows   ifdef  WIN32      ifdef LIBRARY EXPORTS          define LIBRARY API   declspec dllexport       else          define LIBRARY API   declspec dllimport       endif  elif      define LIBRARY API  endif  When using dllexport dllimport you do not need to use DEF files  if you use DEF files you do not need to use dllexport dllimport   The two methods accomplish the same task different ways  I believe that dllexport dllimport is the recommended method out of the two  Exporting unmangled functions from a C   DLL for LoadLibrary PInvoke If you need this to use LoadLibrary and GetProcAddress  or maybe importing from another language  i e PInvoke from  NET  or FFI in Python R etc  you can use extern  quot C quot  inline with your dllexport to tell the C   compiler not to mangle the names   And since we are using GetProcAddress instead of dllimport we don t need to do the ifdef dance from above  just a simple dllexport  The Code   define EXTERN DLL EXPORT extern  quot C quot    declspec dllexport   EXTERN DLL EXPORT int getEngineVersion       return 1     EXTERN DLL EXPORT void registerPlugin Kernel  amp K      K getGraphicsServer   addGraphicsDriver      auto ptr lt GraphicsServer  GraphicsDriver gt  new OpenGLGraphicsDriver            And here s what the exports look like with Dumpbin  exports    Dump of file opengl plugin dll    File Type  DLL    Section contains the following exports for opengl plugin dll      00000000 characteristics     49866068 time date stamp Sun Feb 01 19 54 32 2009         0 00 version            1 ordinal base            2 number of functions            2 number of names      ordinal hint RVA      name            1    0 0001110E getEngineVersion    ILT 265  getEngineVersion            2    1 00011028 registerPlugin    ILT 35  registerPlugin   So this code works fine  m hDLL     LoadLibrary T quot opengl plugin dll quot     m pfnGetEngineVersion   reinterpret cast lt fnGetEngineVersion   gt       GetProcAddress m hDLL   quot getEngineVersion quot      m pfnRegisterPlugin   reinterpret cast lt fnRegisterPlugin   gt       GetProcAddress m hDLL   quot registerPlugin quot

User · Answer

I think  naked might get what you want  but it also prevents the compiler from generating the stack management code for the function  extern  C  causes C style name decoration  Remove that and that should get rid of your   s  The linker doesn t add the underscores  the compiler does  stdcall causes the argument stack size to be appended   For more  see  http   en wikipedia org wiki X86 calling conventions http   www codeproject com KB cpp calling conventions demystified aspx  The bigger question is why do you want to do that  What s wrong with the mangled names

User · Answer

I had exactly the same problem  my solution was to use module definition file   def  instead of   declspec dllexport  to define exports http   msdn microsoft com en-us library d91k01sh aspx   I have no idea why this works  but it does

User · Answer

For C      I just faced the same issue and I think it is worth mentioning  a problem comes up when one use both    stdcall  or WINAPI  and extern  C    As you know extern  C  removes the decoration so that instead of      declspec dllexport  int Test void                         -- gt  dumpbin    Test  YaHXZ   you obtain a symbol name undecorated   extern  C    declspec dllexport  int Test void              -- gt  dumpbin   Test   However the  stdcall     macro WINAPI  that changes the calling convention   also decorates names so that if we use both we obtain       extern  C    declspec dllexport  int WINAPI Test void    -- gt  dumpbin    Test 0   and the benefit of extern  C  is lost because the symbol is decorated  with    bytes       Note that this only occurs for x86 architecture because   the   stdcall convention is ignored on x64  msdn   on x64 architectures  by convention  arguments are passed in registers when possible  and subsequent arguments are passed on the stack      This is particularly tricky if you are targeting both x86 and x64 platforms     Two solutions    Use a definition file  But this forces you to maintain the state of the def file  the simplest way   define the macro  see msdn           define EXPORT  comment linker    EXPORT     FUNCTION           FUNCDNAME      and then include the following pragma in the function body    pragma EXPORT   Full Example     int WINAPI Test void         pragma EXPORT     return 1      This will export the function undecorated for both x86 and x64 targets while preserving the   stdcall convention for x86  The   declspec dllexport  is not required in this case

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