Conversion Problem In Muｌｔi Byte to Wide Char

[developerid]

Hi, I am working on a Unicode Conversion Module and facing this problem..

I have define
typedef basic_string<TCHAR> tstring;

tstring strFirstMsg;
tstring strSecondMsg;

these two string contains the value which I took, from the input RTF String.
these 2 strings some value in a lang. say chinese..
Now I have to calculate its Unicode Equavalant..

For this I used

wchar_t szUnicodeBuffer[200];
strTempUniCode.assign(strFirstMsg);
strTempUniCode.append(strSecondMsg);

int iWriteByte = 0;

iWriteByte = MultiByteToWideChar(nCodePage, MB_COMPOSITE, strTempUniCode,strTempUniCode.length(),szUnicodeBuffer, 100);

It gives error
error C2664: 'MultiByteToWideChar' : cannot convert parameter 3 from 'class std::basic_string<unsigned short,struct std::char_traits<unsigned short>,class std::allocator<unsigned s
hort> >' to 'const char *'

after this error Itried like this

iWriteByte = MultiByteToWideChar(nCodePage, MB_COMPOSITE, (const char*)strTempUniCode.c_str(),strTempUniCode.length(),szUnicodeBuffer, 100);

In this case error was removed, but the output was not correct.

I can NOT　ＵＳＥ　ＭＦＣ．

can u suggest what I should do...

Regs