HOWTO: Convert from ANSI to Unicode & Unicode to ANSI for OLE

• Microsoft OLE Libraries, used with:
  • Microsoft Windows NT, versions 3.51, 4.0
  • Microsoft Windows 95

SUMMARY

All strings that are passed to and received from 32-bit OLE APIs and interface methods use Unicode. This requires applications that use ANSI strings to convert them to Unicode before passing them to OLE and to convert the Unicode strings that are received from OLE to ANSI. This article demonstrates how these conversions can be done.

MORE INFORMATION

Windows NT implements Unicode (or wide character) and ANSI versions of Win32 functions that take string parameters. However Windows 95 does not implement the Unicode version of most Win32 functions that take string parameters. Instead it implements only the ANSI versions of these functions.

A major exception to this rule is 32-bit OLE. 32-bit OLE APIs and interface methods on Windows NT and Windows 95 use Unicode exclusively. ANSI versions of these functions are not implemented either on Windows NT or Windows 95.

This means that a 32-bit application that needs to run on both Windows 95 and Windows NT must use the ANSI versions of the non-OLE Win32 functions and must convert ANSI strings to Unicode before they are passed to OLE.

A 32-bit Unicode application that runs only on Windows NT need not use any ANSI/Unicode conversion functions.

Win32 provides MultiByteToWideChar and WideCharToMultiByte to convert ANSI strings to Unicode and Unicode strings to ANSI. This article provides AnsiToUnicode and UnicodeToAnsi, which uses these functions for ANSI/Unicode conversion.

/*
 * AnsiToUnicode converts the ANSI string pszA to a Unicode string
 * and returns the Unicode string through ppszW. Space for the
 * the converted string is allocated by AnsiToUnicode.
 */ 

HRESULT __fastcall AnsiToUnicode(LPCSTR pszA, LPOLESTR* ppszW)
{

    ULONG cCharacters;
    DWORD dwError;

    // If input is null then just return the same.
    if (NULL == pszA)
    {
        *ppszW = NULL;
        return NOERROR;
    }

    // Determine number of wide characters to be allocated for the
    // Unicode string.
    cCharacters =  strlen(pszA)+1;

    // Use of the OLE allocator is required if the resultant Unicode
    // string will be passed to another COM component and if that
    // component will free it. Otherwise you can use your own allocator.
    *ppszW = (LPOLESTR) CoTaskMemAlloc(cCharacters*2);
    if (NULL == *ppszW)
        return E_OUTOFMEMORY;

    // Covert to Unicode.
    if (0 == MultiByteToWideChar(CP_ACP, 0, pszA, cCharacters,
                  *ppszW, cCharacters))
    {
        dwError = GetLastError();
        CoTaskMemFree(*ppszW);
        *ppszW = NULL;
        return HRESULT_FROM_WIN32(dwError);
    }

    return NOERROR;
/*
 * UnicodeToAnsi converts the Unicode string pszW to an ANSI string
 * and returns the ANSI string through ppszA. Space for the
 * the converted string is allocated by UnicodeToAnsi.
 */ 

HRESULT __fastcall UnicodeToAnsi(LPCOLESTR pszW, LPSTR* ppszA)
{

    ULONG cbAnsi, cCharacters;
    DWORD dwError;

    // If input is null then just return the same.
    if (pszW == NULL)
    {
        *ppszA = NULL;
        return NOERROR;
    }

    cCharacters = wcslen(pszW)+1;
    // Determine number of bytes to be allocated for ANSI string. An
    // ANSI string can have at most 2 bytes per character (for Double
    // Byte Character Strings.)
    cbAnsi = cCharacters*2;

    // Use of the OLE allocator is not required because the resultant
    // ANSI  string will never be passed to another COM component. You
    // can use your own allocator.
    *ppszA = (LPSTR) CoTaskMemAlloc(cbAnsi);
    if (NULL == *ppszA)
        return E_OUTOFMEMORY;

    // Convert to ANSI.
    if (0 == WideCharToMultiByte(CP_ACP, 0, pszW, cCharacters, *ppszA,
                  cbAnsi, NULL, NULL))
    {
        dwError = GetLastError();
        CoTaskMemFree(*ppszA);
        *ppszA = NULL;
        return HRESULT_FROM_WIN32(dwError);
    }
    return NOERROR;

} 

// The following code gets an ANSI filename that is specified by the
// user in the OpenFile common dialog. This file name is converted into
// a Unicode string and is passed to the OLE API CreateFileMoniker. The
// Unicode string is then freed.

OPENFILENAME ofn;
LPOLESTR pszFileNameW;
LPMONIKER pmk;
:

// Get file name from OpenFile Common Dialog. The ANSI file name will
// be placed in ofn.lpstrFile

GetOpenFileName(&ofn);
:
AnsiToUnicode(ofn.lpstrFile, &pszFileNameW);
CreateFileMoniker(pszFileNameW, &pmk);
CoTaskMemFree(pszFileNameW);

// The following code implements IOleInPlaceFrame::SetStatusText.
// The lpszStatusText string, that is received from another OLE
// component, uses Unicode. The string is converted to ANSI before it is
// passed to the ANSI version of SetWindowText. Windows 95 supports only
// the ANSI version of SetWindowText.

COleInPlaceFrame::SetStatusText(LPCOLESTR pszStatusTextW)
{

    LPSTR pszStatusTextA;
    UnicodeToAnsi(pszStatusTextW, &pszStatusTextA);
    SetWindowText(m_hwndStatus, pszStatusTextA);
    CoTaskMemFree(pszStatusTextA);

} 

CreateFileMoniker(OLESTR("c:\\boo\\har.doc"), &pmk); 

USES_CONVERSION;
GetOpenFileName(&ofn);
CreateFileMoniker(T2OLE(ofn.lpstrFile), &pmk); 

inline LPOLESTR T2OLE(LPTSTR lp) { return lp; } 

#define T2OLE(lpa) A2W(lpa) 

#define A2W(lpa) (\ 
        ((LPCSTR)lpa == NULL) ? NULL : (\ 
            _convert = (strlen(lpa)+1),\ 
            AfxA2WHelper((LPWSTR) alloca(_convert*2), lpa, _convert)\ 
        )\ 

) 

GetOpenFileName(&ofn);
CreateFileMoniker(String16(ofn.lpstrFile), &pmk); 

// String16 //////////////////////////////////////////////////////// 
// Shim class that converts both 8-bit (foreign) and
// 16-bit (native) strings to 16-bit wideness

class String16 {
public:

// native and foreign constructors
    String16(const char *p8);
    String16(const wchar_t *p16);

// non-virtual destructor (this class is concrete)

  ~String16(void);

// native conversion operator

  operator const wchar_t * (void) const;
private:

// native wideness string
    wchar_t *m_sz;
// is foreign??
    BOOL m_bIsForeign;

// protect against assignment!

  String16(const String16&);

    String16& operator=(const String16&);
};

// native constructor is a pass-through

inline String16::String16(const wchar_t *p16)
: m_sz((wchar_t *)p16), m_bIsForeign(FALSE)
{
}

// simply give out the native wideness string

inline String16::operator const wchar_t * (void) const
{
  return m_sz;
}

// foreign constructor requires allocation of a native
// string and conversion

inline String16::String16(const char *p8)
: m_bIsForeign(TRUE)
{

// calculate string length

  size_t len = strlen(p8);

// calculate required buffer size (some characters may
// already occupy 16-bits under DBCS)

  size_t size = mbstowcs(0, p8, len) + 1;

// alloc native string and convert

  if (m_sz = new wchar_t[size])

    mbstowcs(m_sz, p8, size);

}

// delete native string only if synthesized in foreign constructor

inline String16::~String16(void) {
  if (m_bIsForeign)

    delete[] m_sz;

} 

Additional query words: convert helper routines functions

Keywords : kbcode kbole kbprg kbNTOS351 kbNTOS400 kbWinOS95 kbGrpCom kbDSupport kbhowto
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Issue type : kbhowto