using unicode dlls in MBCS projects or vice versa - c++

Question

I have a vc++ dll that is compiled with charset set to 'Use Unicode Character Set'.
Now i want to use this dll in my vc++ exe whose charset is 'Use Multi-Byte Character Set'. I know that theoretically nothing stops me from doing this as after compiling the vc++ dll, all the function signatures would be either wchar_t or LPCWSTRs .. And in my vc++ exe i just create strings of that format and call the exported functions. But, The problem i am facing is , The header in unicode dll takes TCHAR parameters like for ex:
class MYLIBRARY_EXPORT PrintableInt
{
public:
PrintableInt(int value);
...
void PrintString(TCHAR* somestr);
private:
int m_val;
};
Now i want to use this PrintString() in my exe. So, I included the header and used it like below:
#include "unicodeDllHeaders.h"
PrintableInt p(2);
wchar_t* someStr = L"Some str";
p.PrintString(someStr);
This as expected gives me a compiler error :
error C2664: 'PrintableInt::PrintString' : cannot convert parameter 1 from 'wchar_t *' to 'TCHAR *'
As the exe is built with MBCS TCHAR is defined to char . So, what i thought would solve this issue is :
#define _UNICODE
#include "unicodeDllHeaders.h"
#undef _UNICODE
But after defining _UNICODE also i still get the compilation error. So, my next guess was that probably TCHAR.h was already included before the #include "unicodeDllHeaders.h" , when i searched for the inclusion of TCHAR.h it was there else where in the project. So, I moved the inclusion to after definition of _UNICODE , This solved the compilation error here but it is failing in the other places where TCHAR is expected to be made char . So, My question is :
Can i somehow make TCHAR resolve to char and wchar_t in the same project ? I tried #define TCHAR char, #undef TCHAR , #define TCHAR wchar_t but its failing in the c headers like xutils

Answer 1

You can not retroactively change the binary interface of your DLL, regardless of what do to your header file by using macros. The typical solution is to firstly dump the whole legacy MBCS stuff. This stopped being interesting 10 years ago, nowadays all targets supporting the win32 API support the wide character interface with full Unicode support.
If you want that retro feeling of the nineties, you can also compile your DLL twice, once with CHAR and once with WCHAR. The latter then typically get a "u" suffix (for Unicode). In your header, you then check the charset and delegate to the according DLL using #pragma comment lib...