MultiByteToWideChar
WideCharToMultiByte

例程:
char ToGBTable[0xffff][3];

memset(ToGBTable, 0, sizeof(ToGBTable));

for(wchar i=0; i++; i<0xffff)
{
  if (i<0xff)
  {
    ToGBTable[i][0] = (char)i;
  }
  else
  {
     WideCharToMultiByte(CP_ACP
                         WC_DEFAULTCHAR,
                         &i,
                         1,
                         ToGBTable[i],
                         3,
                         "?",
                         NULL);
  }
}

CharToUnicode(BYTE* buf, DWORD bufSize)
{
 CString csTemp;
 WCHAR *UnicodeStr=new WCHAR[bufSize+1];
 DWORD UnicodeSize=MultiByteToWideChar(CP_ACP,0,
             (LPCSTR)buf,bufSize+1,UnicodeStr,(DWORD)bufSize+1);
 csTemp=UnicodeStr;
 delete [] UnicodeStr;
}

The Windows function MultiByteToWideChar converts multibyte-character strings to wide-character strings.
int MultiByteToWideChar(

    UINT CodePage, // code page
    DWORD dwFlags, // character-type options
    LPCSTR lpMultiByteStr, // address of string to map
    int cchMultiByte, // number of characters in string
    LPWSTR lpWideCharStr, // address of wide-character buffer
    int cchWideChar  // size of buffer
   );

#include <string.h>
#include "CharsetConversion.h"

int AsciiToUnicode(const char * szAscii, wchar_t * szUnicode)
{
 int len, i;

 if((szUnicode == NULL) || (szAscii == NULL))
  return 0;

 len = strlen(szAscii);

 for(i=0;i<len+1;i++)
  *szUnicode++ = static_cast<wchar_t>(*szAscii++);

 return i;
}

int UnicodeToAscii(const wchar_t * szUnicode, char * szAscii)
{
 int len, i;

 if((szUnicode == NULL) || (szAscii == NULL))
  return 0;

 len = wcslen(szUnicode);

 for(i=0;i<len+1;i++)
  *szAscii++ = static_cast<char>(*szUnicode++);

 return i;
}

_T or _TEXT
converts following character or string to its Unicode counterpart

HRESULT __fastcall AnsiToUnicode(LPCSTR pszA, LPOLESTR* ppszW)
{
    ULONG cCharacters;
    DWORD dwError;
    if (NULL == pszA)
    {
        *ppszW = NULL;
        return NOERROR;
    }
    cCharacters =  strlen(pszA)+1;
    *ppszW = (LPOLESTR) CoTaskMemAlloc(cCharacters*2);
    if (NULL == *ppszW)
        return E_OUTOFMEMORY;
    if (0 == MultiByteToWideChar(CP_ACP, 0, pszA, cCharacters,*ppszW, cCharacters))
    {
        dwError = GetLastError();
        CoTaskMemFree(*ppszW);
        *ppszW = NULL;
        return HRESULT_FROM_WIN32(dwError);
    }

    return NOERROR;
}