CStdioFile扩展（支持Ansi、Unicode、Utf-8等文本格式）

头文件声明（CStdioFileEx.h）：

// StdioFileEx.h: interface for the CStdioFileEx class.
//
// Version 1.1 23 August 2003.	Incorporated fixes from Dennis Jeryd.
// Version 1.3 19 February 2005. Incorporated fixes from Howard J Oh and some of my own.
// Version 1.4 26 February 2005. Fixed stupid screw-up in code from 1.3.
// Version 1.5 18 November 2005. - Incorporated fixes from Andy Goodwin.
//											- Allows code page to be specified for reading/writing
//											- Properly calculates multibyte buffer size instead of
//												assuming lstrlen(s).
//											- Should handle UTF8 properly.
//
// Copyright David Pritchard 2003-2005. davidpritchard@ctv.es
//
// You can use this class freely, but please keep my ego happy 
// by leaving this comment in place.
//
//

#if !defined(AFX_STDIOFILEEX_H__41AFE3CA_25E0_482F_8B00_C40775BCDB81__INCLUDED_)
#define AFX_STDIOFILEEX_H__41AFE3CA_25E0_482F_8B00_C40775BCDB81__INCLUDED_

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

#define	nUNICODE_BOM					0xFEFF		// Unicode "byte order mark" which goes at start of file
#define	nUTF8_BOM						0xEFBBBF	// utf-8
#define	sNEWLINE						_T("\r\n")	// New line characters
#define	sDEFAULT_UNICODE_FILLER_CHAR	"#"			// Filler char used when no conversion from Unicode to local code page is possible

class CStdioFileEx : public CStdioFile
{
public:
	CStdioFileEx();
	CStdioFileEx(LPCTSTR lpszFileName, UINT nOpenFlags);

	virtual BOOL	Open(LPCTSTR lpszFileName, UINT nOpenFlags, CFileException* pError = NULL);
	virtual BOOL	ReadString(CString& rString);
	virtual void	WriteString(LPCTSTR lpsz);
	bool			IsFileUnicodeText() { return m_bIsUnicodeText; }
	bool			IsFileUtf8Text() { return m_bIsUtf8Text; }
	unsigned long	GetCharCount();

	// Additional flag to allow Unicode text writing
	static const UINT modeWriteUnicode;

	void			SetCodePage(IN const UINT nCodePage);

	// static utility functions

	// --------------------------------------------------------------------------------------------
	//
	//	CStdioFileEx::GetUnicodeStringFromMultiByteString()
	//
	// --------------------------------------------------------------------------------------------
	// Returns:    int - num. of chars written (0 means error)
	// Parameters:	char *		szMultiByteString	(IN)		Multi-byte input string
	//				wchar_t*	szUnicodeString		(OUT)		Unicode outputstring
	//				int			nUnicodeBufferSize	(IN)		Size of Unicode output buffer (chars) (IN)
	//				int			nCodePage			(IN)		Code page used to perform conversion
	//																Default = -1 (Get local code page).
	//
	// Purpose:		Gets a Unicode string from a MultiByte string.
	// Notes:		None.
	// Exceptions:	None.
	//
	static int		GetUnicodeStringFromMultiByteString(IN LPCSTR szMultiByteString, OUT wchar_t* szUnicodeString, IN int nUnicodeBufferSize, IN int nCodePage = -1);

	// --------------------------------------------------------------------------------------------
	//
	//	CStdioFileEx::GetMultiByteStringFromUnicodeString()
	//
	// --------------------------------------------------------------------------------------------
	// Returns:    int - number of characters written. 0 means error
	// Parameters:	wchar_t *	szUnicodeString			(IN)	Unicode input string
	//				char*		szMultiByteString		(OUT)	Multibyte output string
	//				int			nMultiByteBufferSize	(IN)	Multibyte buffer size
	//				int			nCodePage				(IN)	Code page used to perform conversion
	//																Default = -1 (Get local code page).
	//
	// Purpose:		Gets a MultiByte string from a Unicode string.
	// Notes:		.
	// Exceptions:	None.
	//
	static int		GetMultiByteStringFromUnicodeString(wchar_t* szUnicodeString, char* szMultiByteString,
		int nMultiByteBufferSize, int nCodePage = -1);

	//---------------------------------------------------------------------------------------------------
	//
	//	CStdioFileEx::GetRequiredMultiByteLengthForUnicodeString()
	//
	//---------------------------------------------------------------------------------------------------
	// Returns:    int
	// Parameters: wchar_t * szUnicodeString,int nCodePage=-1
	//
	// Purpose:		Obtains the multi-byte buffer size needed to accommodate a converted Unicode string.
	//	Notes:		We can't assume that the buffer length is simply equal to the number of characters
	//					because that wouldn't accommodate multibyte characters!
	//
	static int		GetRequiredMultiByteLengthForUnicodeString(wchar_t* szUnicodeString, int nCodePage = -1);


	// --------------------------------------------------------------------------------------------
	//
	//	CStdioFileEx::IsFileUnicode()
	//
	// --------------------------------------------------------------------------------------------
	// Returns:    bool
	// Parameters: const CString& sFilePath
	//
	// Purpose:		Determines whether a file is Unicode by reading the first character and detecting
	//					whether it's the Unicode byte marker.
	// Notes:		None.
	// Exceptions:	None.
	//
	static bool IsFileUnicode(const CString& sFilePath);
	
	static bool IsFileUtf8(const CString& sFilePath);

	static UINT	GetCurrentLocaleCodePage();

protected:
	UINT	ProcessFlags(const CString& sFilePath, UINT& nOpenFlags);

	bool	m_bIsUnicodeText;
	bool	m_bIsUtf8Text;
	UINT	m_nFlags;
	int		m_nFileCodePage;
};

#endif // !defined(AFX_STDIOFILEEX_H__41AFE3CA_25E0_482F_8B00_C40775BCDB81__INCLUDED_)

源码定义（CStdioFileEx.cpp）：

// StdioFileEx.cpp: implementation of the CStdioFileEx class.
//
// Version 1.1 23 August 2003.	Incorporated fixes from Dennis Jeryd.
// Version 1.3 19 February 2005. Incorporated fixes from Howard J Oh and some of my own.
// Version 1.4 26 February 2005. Fixed stupid screw-up in code from 1.3.
// Version 1.5 18 November 2005. - Incorporated fixes from Andy Goodwin.
//											- Allows code page to be specified for reading/writing
//											- Properly calculates multibyte buffer size instead of
//												assuming lstrlen(s).
//											- Should handle UTF8 properly.
//
// Copyright David Pritchard 2003-2005. davidpritchard@ctv.es
//
// You can use this class freely, but please keep my ego happy 
// by leaving this comment in place.
//
//

#include "stdafx.h"
#include "CStdioFileEx.h"

#ifdef _DEBUG
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#define new DEBUG_NEW
#endif

//
// Construction/Destruction
//

/*static*/ const UINT CStdioFileEx::modeWriteUnicode = 0x20000; // Add this flag to write in Unicode

CStdioFileEx::CStdioFileEx() 
	: CStdioFile()
{
	m_bIsUnicodeText = false;
	m_nFileCodePage = -1;
	m_bIsUtf8Text = false;
	m_nFlags = CFile::typeText | CFile::modeReadWrite;
}

CStdioFileEx::CStdioFileEx(LPCTSTR lpszFileName, UINT nOpenFlags)
	:CStdioFile(lpszFileName, ProcessFlags(lpszFileName, nOpenFlags))
{
	m_nFileCodePage = -1;
}

void CStdioFileEx::SetCodePage(IN const UINT nCodePage)
{
	m_nFileCodePage = (int)nCodePage;
}

BOOL CStdioFileEx::Open(LPCTSTR lpszFileName, UINT nOpenFlags, CFileException* pError /*=NULL*/)
{
	// Process any Unicode stuff
	ProcessFlags(lpszFileName, nOpenFlags);
	if (m_bIsUtf8Text)
		SetCodePage(CP_UTF8);
	return CStdioFile::Open(lpszFileName, nOpenFlags, pError);
}

BOOL CStdioFileEx::ReadString(CString& rString)
{
	const int	nMAX_LINE_CHARS = 4096;
	BOOL		bReadData = FALSE;
	LPTSTR		lpsz;
	int			nLen = 0;
	wchar_t* pszUnicodeString = NULL;
	char* pszMultiByteString = NULL;
	int			nChars = 0;

	try
	{
		// If at position 0, discard byte-order mark before reading
		if (!m_pStream || (GetPosition() == 0 && m_bIsUnicodeText))
		{
			wchar_t	cDummy;
			//		Read(&cDummy, sizeof(_TCHAR));
			Read(&cDummy, sizeof(wchar_t));
		}

		// If compiled for Unicode
#ifdef _UNICODE
		if (m_bIsUnicodeText)
		{
			// Do standard stuff - Unicode to Unicode. Seems to work OK.
			bReadData = CStdioFile::ReadString(rString);
		}
		else
		{
			pszUnicodeString = new wchar_t[nMAX_LINE_CHARS];
			pszMultiByteString = new char[nMAX_LINE_CHARS];

			// Initialise to something safe
			memset(pszUnicodeString, 0, sizeof(wchar_t) * nMAX_LINE_CHARS);
			memset(pszMultiByteString, 0, sizeof(char) * nMAX_LINE_CHARS);

			// Read the string
			bReadData = (NULL != fgets(pszMultiByteString, nMAX_LINE_CHARS, m_pStream));

			if (bReadData)
			{
				// Convert multibyte to Unicode, using the specified code page
				nChars = GetUnicodeStringFromMultiByteString(pszMultiByteString, pszUnicodeString, nMAX_LINE_CHARS, m_nFileCodePage);

				if (nChars > 0)
				{
					rString = (CString)pszUnicodeString;
				}
			}
		}
#else

		if (!m_bIsUnicodeText)
		{
			// Do standard stuff -- read ANSI in ANSI
			bReadData = CStdioFile::ReadString(rString);

			// Get the current code page
			UINT nLocaleCodePage = GetCurrentLocaleCodePage();

			// If we got it OK...
			if (nLocaleCodePage > 0)
			{
				// if file code page does not match the system code page, we need to do a double conversion!
				if (nLocaleCodePage != (UINT)m_nFileCodePage)
				{
					int nStringBufferChars = rString.GetLength() + 1;

					pszUnicodeString = new wchar_t[nStringBufferChars];

					// Initialise to something safe
					memset(pszUnicodeString, 0, sizeof(wchar_t) * nStringBufferChars);

					// Convert to Unicode using the file code page
					nChars = GetUnicodeStringFromMultiByteString(rString, pszUnicodeString, nStringBufferChars, m_nFileCodePage);

					// Convert back to multibyte using the system code page
					// (This doesn't really confer huge advantages except to avoid "mangling" of non-convertible special
					// characters. So, if a file in the E.European code page is displayed on a system using the 
					// western European code page, special accented characters which the system cannot display will be
					// replaced by the default character (a hash or something), rather than being incorrectly mapped to
					// other, western European accented characters).
					if (nChars > 0)
					{
						// Calculate how much we need for the MB buffer (it might be larger)
						nStringBufferChars = GetRequiredMultiByteLengthForUnicodeString(pszUnicodeString, nLocaleCodePage);
						pszMultiByteString = new char[nStringBufferChars];

						nChars = GetMultiByteStringFromUnicodeString(pszUnicodeString, pszMultiByteString, nStringBufferChars, nLocaleCodePage);
						rString = (CString)pszMultiByteString;
					}
				}
			}
		}
		else
		{
			pszUnicodeString = new wchar_t[nMAX_LINE_CHARS];

			// Initialise to something safe
			memset(pszUnicodeString, 0, sizeof(wchar_t) * nMAX_LINE_CHARS);

			// Read as Unicode, convert to ANSI

			// Bug fix by Dennis Jeryd 06/07/2003: initialise bReadData
			bReadData = (NULL != fgetws(pszUnicodeString, nMAX_LINE_CHARS, m_pStream));

			if (bReadData)
			{
				// Calculate how much we need for the multibyte string
				int nRequiredMBBuffer = GetRequiredMultiByteLengthForUnicodeString(pszUnicodeString, m_nFileCodePage);
				pszMultiByteString = new char[nRequiredMBBuffer];

				nChars = GetMultiByteStringFromUnicodeString(pszUnicodeString, pszMultiByteString, nRequiredMBBuffer, m_nFileCodePage);

				if (nChars > 0)
				{
					rString = (CString)pszMultiByteString;
				}
			}

		}
#endif

		// Then remove end-of-line character if in Unicode text mode
		if (bReadData)
		{
			// Copied from FileTxt.cpp but adapted to Unicode and then adapted for end-of-line being just '\r'. 
			nLen = rString.GetLength();
			if (nLen > 1 && rString.Mid(nLen - 2) == sNEWLINE)
			{
				rString.GetBufferSetLength(nLen - 2);
			}
			else
			{
				lpsz = rString.GetBuffer(0);
				if (nLen != 0 && (lpsz[nLen - 1] == _T('\r') || lpsz[nLen - 1] == _T('\n')))
				{
					rString.GetBufferSetLength(nLen - 1);
				}
			}
		}
	}
	// Ensure we always delete in case of exception
	catch (...)
	{
		if (pszUnicodeString)	delete[] pszUnicodeString;

		if (pszMultiByteString) delete[] pszMultiByteString;

		throw;
	}

	if (pszUnicodeString)		delete[] pszUnicodeString;

	if (pszMultiByteString)		delete[] pszMultiByteString;

	return bReadData;
}



// --------------------------------------------------------------------------------------------
//
//	CStdioFileEx::WriteString()
//
// --------------------------------------------------------------------------------------------
// Returns:    void
// Parameters: LPCTSTR lpsz
//
// Purpose:		Writes string to file either in Unicode or multibyte, depending on whether the caller specified the
//					CStdioFileEx::modeWriteUnicode flag. Override of base class function.
// Notes:		If writing in Unicode we need to:
//						a) Write the Byte-order-mark at the beginning of the file
//						b) Write all strings in byte-mode
//					-	If we were compiled in Unicode, we need to convert Unicode to multibyte if 
//						we want to write in multibyte
//					-	If we were compiled in multi-byte, we need to convert multibyte to Unicode if 
//						we want to write in Unicode.
// Exceptions:	None.
//
void CStdioFileEx::WriteString(LPCTSTR lpsz)
{
	wchar_t* pszUnicodeString = NULL;
	char* pszMultiByteString = NULL;

	try
	{
		// If writing Unicode and at the start of the file, need to write byte mark
		if (m_nFlags & CStdioFileEx::modeWriteUnicode)
		{
			// If at position 0, write byte-order mark before writing anything else
			if (!m_pStream || GetPosition() == 0)
			{
				wchar_t cBOM = (wchar_t)nUNICODE_BOM;
				CFile::Write(&cBOM, sizeof(wchar_t));
			}
		}

		// If compiled in Unicode...
#ifdef _UNICODE

		// If writing Unicode, no conversion needed
		if (m_nFlags & CStdioFileEx::modeWriteUnicode)
		{
			// Write in byte mode
			CFile::Write(lpsz, lstrlen(lpsz) * sizeof(wchar_t));
		}
		// Else if we don't want to write Unicode, need to convert
		else
		{
			int		nChars = lstrlen(lpsz) + 1;				// Why plus 1? Because yes
//			int		nBufferSize = nChars * sizeof(char);	// leave space for multi-byte chars
			int		nCharsWritten = 0;
			int		nBufferSize = 0;

			pszUnicodeString = new wchar_t[nChars];

			// Copy string to Unicode buffer
			lstrcpy(pszUnicodeString, lpsz);

			// Work out how much space we need for the multibyte conversion
			nBufferSize = GetRequiredMultiByteLengthForUnicodeString(pszUnicodeString, m_nFileCodePage);
			pszMultiByteString = new char[nBufferSize];

			// Get multibyte string
			nCharsWritten = GetMultiByteStringFromUnicodeString(pszUnicodeString, pszMultiByteString, nBufferSize, m_nFileCodePage);

			if (nCharsWritten > 0)
			{
				// Do byte-mode write using actual chars written (fix by Howard J Oh)
	//			CFile::Write((const void*)pszMultiByteString, lstrlen(lpsz));
				CFile::Write((const void*)pszMultiByteString,
					nCharsWritten * sizeof(char));
			}
		}
		// Else if *not* compiled in Unicode
#else
		// If writing Unicode, need to convert
		if (m_nFlags & CStdioFileEx::modeWriteUnicode)
		{
			int		nChars = lstrlen(lpsz) + 1;	 // Why plus 1? Because yes
			int		nBufferSize = nChars * sizeof(wchar_t);
			int		nCharsWritten = 0;

			pszUnicodeString = new wchar_t[nChars];
			pszMultiByteString = new char[nChars];

			// Copy string to multibyte buffer
			lstrcpy(pszMultiByteString, lpsz);

			nCharsWritten = GetUnicodeStringFromMultiByteString(pszMultiByteString, pszUnicodeString, nChars, m_nFileCodePage);

			if (nCharsWritten > 0)
			{
				// Do byte-mode write using actual chars written (fix by Howard J Oh)
	//			CFile::Write(pszUnicodeString, lstrlen(lpsz) * sizeof(wchar_t));
				CFile::Write(pszUnicodeString, nCharsWritten * sizeof(wchar_t));
			}
			else
			{
				ASSERT(false);
			}

		}
		// Else if we don't want to write Unicode, no conversion needed, unless the code page differs
		else
		{
			//		// Do standard stuff
			//		CStdioFile::WriteString(lpsz);

					// Get the current code page
			UINT nLocaleCodePage = GetCurrentLocaleCodePage();

			// If we got it OK, and if file code page does not match the system code page, we need to do a double conversion!
			if (nLocaleCodePage > 0 && nLocaleCodePage != (UINT)m_nFileCodePage)
			{
				int	nChars = lstrlen(lpsz) + 1;	 // Why plus 1? Because yes

				pszUnicodeString = new wchar_t[nChars];

				// Initialise to something safe
				memset(pszUnicodeString, 0, sizeof(wchar_t) * nChars);

				// Convert to Unicode using the locale code page (the code page we are using in memory)
				nChars = GetUnicodeStringFromMultiByteString((LPCSTR)(const char*)lpsz, pszUnicodeString, nChars, nLocaleCodePage);

				// Convert back to multibyte using the file code page
				// (Note that you can't reliably read a non-Unicode file written in code page A on a system using a code page B,
				// modify the file and write it back using code page A, unless you disable all this double-conversion code.
				// In effect, you have to choose between a mangled character display and mangled file writing).
				if (nChars > 0)
				{
					// Calculate how much we need for the MB buffer (it might be larger)
					nChars = GetRequiredMultiByteLengthForUnicodeString(pszUnicodeString, m_nFileCodePage);

					pszMultiByteString = new char[nChars];
					memset(pszMultiByteString, 0, sizeof(char) * nChars);

					nChars = GetMultiByteStringFromUnicodeString(pszUnicodeString, pszMultiByteString, nChars, m_nFileCodePage);

					// Do byte-mode write. This avoids annoying "interpretation" of \n's as \r\n
					CFile::Write((const void*)pszMultiByteString, nChars * sizeof(char));
				}
			}
			else
			{
				// Do byte-mode write. This avoids annoying "interpretation" of \n's as \r\n
				CFile::Write((const void*)lpsz, lstrlen(lpsz) * sizeof(char));
			}
		}

#endif
	}
	// Ensure we always clean up
	catch (...)
	{
		if (pszUnicodeString)	delete[] pszUnicodeString;
		if (pszMultiByteString)	delete[] pszMultiByteString;
		throw;
	}

	if (pszUnicodeString)	delete[] pszUnicodeString;
	if (pszMultiByteString)	delete[] pszMultiByteString;
}

UINT CStdioFileEx::ProcessFlags(const CString& sFilePath, UINT& nOpenFlags)
{
	m_bIsUnicodeText = false;
	m_bIsUtf8Text = false;

	// If we have writeUnicode we must have write or writeRead as well
#ifdef _DEBUG
	if (nOpenFlags & CStdioFileEx::modeWriteUnicode)
	{
		ASSERT(nOpenFlags & CFile::modeWrite || nOpenFlags & CFile::modeReadWrite);
	}
#endif

	// If reading in text mode and not creating... ; fixed by Dennis Jeryd 6/8/03
	if (nOpenFlags & CFile::typeText && !(nOpenFlags & CFile::modeCreate) && !(nOpenFlags & CFile::modeWrite))
	{
		m_bIsUnicodeText = IsFileUnicode(sFilePath);
		m_bIsUtf8Text = IsFileUtf8(sFilePath);

		// If it's Unicode, switch to binary mode
		if (m_bIsUnicodeText)
		{
			nOpenFlags ^= CFile::typeText;
			nOpenFlags |= CFile::typeBinary;
		}
	}

	m_nFlags = nOpenFlags;

	return nOpenFlags;
}

// --------------------------------------------------------------------------------------------
//
//	CStdioFileEx::IsFileUnicode()
//
// --------------------------------------------------------------------------------------------
// Returns:    bool
// Parameters: const CString& sFilePath
//
// Purpose:		Determines whether a file is Unicode by reading the first character and detecting
//					whether it's the Unicode byte marker.
// Notes:		None.
// Exceptions:	None.
//
/*static*/ bool CStdioFileEx::IsFileUnicode(const CString& sFilePath)
{
	CFile			file;
	bool			bIsUnicode = false;
	wchar_t			cFirstChar;
	CFileException	exFile;

	// Open file in binary mode and read first character
	if (file.Open(sFilePath, CFile::typeBinary | CFile::modeRead, &exFile))
	{
		// If byte is Unicode byte-order marker, let's say it's Unicode
		if (file.Read(&cFirstChar, sizeof(wchar_t)) > 0 && cFirstChar == (wchar_t)nUNICODE_BOM)
		{
			bIsUnicode = true;
		}

		file.Close();
	}
	else
	{
		// Handle error here if you like
	}

	return bIsUnicode;
}

/*static*/ bool CStdioFileEx::IsFileUtf8(const CString& sFilePath)
{
	CFile			file;
	bool			bIsUtf8 = false;
	unsigned char	cFirstChar[3];
	CFileException	exFile;

	// Open file in binary mode and read first character
	if (file.Open(sFilePath, CFile::typeBinary | CFile::modeRead, &exFile))
	{
		// If byte is Unicode byte-order marker, let's say it's Unicode
		if (file.Read(&cFirstChar, sizeof(cFirstChar)) > 0 && cFirstChar[0] == 0xEF && cFirstChar[1] == 0xBB && cFirstChar[2]==0xBF)
		{
			bIsUtf8 = true;
		}

		file.Close();
	}
	else
	{
		// Handle error here if you like
	}

	return bIsUtf8;
}

unsigned long CStdioFileEx::GetCharCount()
{
	int				nCharSize;
	unsigned long	nByteCount, nCharCount = 0;

	if (m_pStream)
	{
		// Get size of chars in file
		nCharSize = m_bIsUnicodeText ? sizeof(wchar_t) : sizeof(char);

		// If Unicode, remove byte order mark from count
		nByteCount = GetLength();

		if (m_bIsUnicodeText)
		{
			nByteCount = nByteCount - sizeof(wchar_t);
		}
		else if (m_bIsUtf8Text)
		{
			nByteCount = nByteCount - 3;
		}

		// Calc chars
		nCharCount = (nByteCount / nCharSize);
	}

	return nCharCount;
}

// Get the current user磗 code page
UINT CStdioFileEx::GetCurrentLocaleCodePage()
{
	_TCHAR	szLocalCodePage[10];
	UINT	nLocaleCodePage = 0;
	int		nLocaleChars = ::GetLocaleInfo(LOCALE_USER_DEFAULT, LOCALE_IDEFAULTANSICODEPAGE, szLocalCodePage, 10);

	// If OK
	if (nLocaleChars > 0)
	{
		nLocaleCodePage = (UINT)_ttoi(szLocalCodePage);
		ASSERT(nLocaleCodePage > 0);
	}
	else
	{
		ASSERT(false);
	}

	// O means either: no ANSI code page (Unicode-only locale?) or failed to get locale
	// In the case of Unicode-only locales, what do multibyte apps do? Answers on a postcard.
	return nLocaleCodePage;
}

// --------------------------------------------------------------------------------------------
//
//	CStdioFileEx::GetUnicodeStringFromMultiByteString()
//
// --------------------------------------------------------------------------------------------
// Returns:    int - num. of chars written (0 means error)
// Parameters:	char *		szMultiByteString	(IN)		Multi-byte input string
//				wchar_t*	szUnicodeString		(OUT)		Unicode outputstring
//				int			nUnicodeBufferSize	(IN)		Size of Unicode output buffer in chars(IN)
//				UINT		nCodePage			(IN)		Code page used to perform conversion
//																Default = -1 (Get local code page).
//
// Purpose:		Gets a Unicode string from a MultiByte string.
// Notes:		None.
// Exceptions:	None.
//
int CStdioFileEx::GetUnicodeStringFromMultiByteString(IN LPCSTR szMultiByteString, OUT wchar_t* szUnicodeString, IN int nUnicodeBufferSize, IN int nCodePage)
{
	bool	bOK = true;
	int		nCharsWritten = 0;

	if (szUnicodeString && szMultiByteString)
	{
		// If no code page specified, take default for system
		if (nCodePage == -1)
		{
			nCodePage = GetACP();
		}

		try
		{
			// Zero out buffer first. NB: nUnicodeBufferSize is NUMBER OF CHARS, NOT BYTES!
			memset((void*)szUnicodeString, '\0', sizeof(wchar_t) *
				nUnicodeBufferSize);

			// When converting to UTF8, don't set any flags (see Q175392).
			nCharsWritten = MultiByteToWideChar((UINT)nCodePage,
				(nCodePage == CP_UTF8 ? 0 : MB_PRECOMPOSED), // Flags
				szMultiByteString, -1, szUnicodeString, nUnicodeBufferSize);
		}
		catch (...)
		{
			TRACE(_T("Controlled exception in MultiByteToWideChar!\n"));
		}
	}

	// Now fix nCharsWritten
	if (nCharsWritten > 0)
	{
		nCharsWritten--;
	}

	//	ASSERT(nCharsWritten > 0);
	return nCharsWritten;
}

// --------------------------------------------------------------------------------------------
//
//	CStdioFileEx::GetMultiByteStringFromUnicodeString()
//
// --------------------------------------------------------------------------------------------
// Returns:    int - number of characters written. 0 means error
// Parameters:	wchar_t *	szUnicodeString			(IN)	Unicode input string
//				char*		szMultiByteString		(OUT)	Multibyte output string
//				int			nMultiByteBufferSize	(IN)	Multibyte buffer size (chars)
//				UINT		nCodePage				(IN)	Code page used to perform conversion
//																Default = -1 (Get local code page).
//
// Purpose:		Gets a MultiByte string from a Unicode string
// Notes:		Added fix by Andy Goodwin: make buffer into int.
// Exceptions:	None.
//
int CStdioFileEx::GetMultiByteStringFromUnicodeString(wchar_t* szUnicodeString, char* szMultiByteString,
	int nMultiByteBufferSize, int nCodePage)
{
	BOOL	bUsedDefChar = FALSE;
	int		nCharsWritten = 0;

	// Fix by Andy Goodwin: don't do anything if buffer is 0
	if (nMultiByteBufferSize > 0)
	{
		if (szUnicodeString && szMultiByteString)
		{
			// Zero out buffer first
			memset((void*)szMultiByteString, '\0', nMultiByteBufferSize);

			// If no code page specified, take default for system
			if (nCodePage == -1)
			{
				nCodePage = GetACP();
			}

			try
			{
				// If writing to UTF8, flags, default char and boolean flag must be NULL
				nCharsWritten = WideCharToMultiByte((UINT)nCodePage,
					(nCodePage == CP_UTF8 ? 0 : WC_COMPOSITECHECK | WC_SEPCHARS), // Flags
					szUnicodeString, -1,
					szMultiByteString,
					nMultiByteBufferSize,
					(nCodePage == CP_UTF8 ? NULL : sDEFAULT_UNICODE_FILLER_CHAR),	// Filler char
					(nCodePage == CP_UTF8 ? NULL : &bUsedDefChar));						// Did we use filler char?

				// If no chars were written and the buffer is not 0, error!
				if (nCharsWritten == 0 && nMultiByteBufferSize > 0)
				{
					TRACE1("Error in WideCharToMultiByte: %d\n", ::GetLastError());
				}
			}
			catch (...)
			{
				TRACE(_T("Controlled exception in WideCharToMultiByte!\n"));
			}
		}
	}

	// Now fix nCharsWritten 
	if (nCharsWritten > 0)
	{
		nCharsWritten--;
	}

	return nCharsWritten;
}

//---------------------------------------------------------------------------------------------------
//
//	CStdioFileEx::GetRequiredMultiByteLengthForUnicodeString()
//
//---------------------------------------------------------------------------------------------------
// Returns:    int
// Parameters: wchar_t * szUnicodeString,int nCodePage=-1
//
// Purpose:		Obtains the multi-byte buffer size needed to accommodate a converted Unicode string.
//	Notes:		We can't assume that the buffer length is simply equal to the number of characters
//					because that wouldn't accommodate multibyte characters!
//
/*static*/ int CStdioFileEx::GetRequiredMultiByteLengthForUnicodeString(wchar_t* szUnicodeString, int nCodePage /*=-1*/)
{
	int nCharsNeeded = 0;

	try
	{
		// If no code page specified, take default for system
		if (nCodePage == -1)
		{
			nCodePage = GetACP();
		}

		// If writing to UTF8, flags, default char and boolean flag must be NULL
		nCharsNeeded = WideCharToMultiByte((UINT)nCodePage,
			(nCodePage == CP_UTF8 ? 0 : WC_COMPOSITECHECK | WC_SEPCHARS), // Flags
			szUnicodeString, -1,
			NULL,
			0,	// Calculate required buffer, please! 
			(nCodePage == CP_UTF8 ? NULL : sDEFAULT_UNICODE_FILLER_CHAR),	// Filler char
			NULL);
	}
	catch (...)
	{
		TRACE(_T("Controlled exception in WideCharToMultiByte!\n"));
	}

	return nCharsNeeded;
}

[*注]：

1、源码摘自互联网，由于具体出处未知，所以未引用源链接地址，如若侵犯版权，请联系博主！

2、源码在原文基础上，添加了对UTF-8 BOM文件类型的支持。