uisng msvc dll from mingw by code::blocks - c++

Question

I have a simple dll build by c++ msvc2010. It create a mydll.dll. (it uses some of windows native dlls so this is a c wrapper. It has function in it
exten "c"
{
void myfunc(std::vector<std::string> &names)
)
Then I use mingw utility pexports.exe and dlltool.exe in mingw\bin folder to convert it.
pexports mydll.dll | sed "s/^_//" > mydll.def
dlltool -U -d mydll.def -l mydll.dll
(overwrite the original one. or rename the original one to mydllold.dll. All dlls are in the same folder of executable of code::blocks program below.)
Then I have a code::blocks project myproc. The compiler is MinGW's g++. It links to the mydll.dll in the property->link settings.
The compilation has no error. But when I run the program
myproc.exe. It has run time error:
mydll.dll is either not designed to run on windows or it contains an error.
When I use:
dlltool -U -d mydll.def -l mydll.a
Then rename mydll.dll to mydllold.dll.
And make myproc link settings to mydll.a, it get error message:
The program cannot start because mydll.dll is missing.
When I rename mydll.a to mydll.dll, it get same error message:
mydll.dll is either not designed to run on windows or it contains an error.
Note. it does not say mydll.a, instead mydll.dll even the link is to mydll.a.
If I rename mydllold.dll back to mydll.dll. The error message is:
The procedure entry point _myfunc could not be located in the dynamic link library mydll.dll.
header file mydll.h:
#ifdef MYDLL_EXPORTS
#define MYDLL_API __declspec(dllexport)
#else
#define MYDLL_API __declspec(dllimport)
#endif
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <vector>
extern "C"
{
MYDLL_API int myfunc(std::vector<std::string>& a);
}
mydll.cpp:
#include <mydll.h>
extern "C"
{
MYDLL_API int myfunc( std::vector<std::string> &a)
{
return 0;
}
}