我也问一个CString的问题：

下面是正确编程：
CString strError;
strError.Format(\"%s%d \",\"Error:\" ,nResult);
AfxMessageBox(strError, MB_ICONERROR);

AfxMessageBox的帮助是：
int AfxMessageBox( LPCTSTR lpszText, UINT nType = MB_OK, UINT nIDHelp = 0 );

Parameters

lpszText

Points to a CString object or null-terminated string containing the message to be displayed in the message box.



上述程序应该是
AfxMessageBox(&strError,MB_ICONERROR);才对啊。
为什么？

Oh,Thank you !

是类的重载起的作用。
AfxMessageBox(&s)的错误是：
none of the 2 overloads can convert parameter 1 from type \'class CString *\'

Cstring有好几个构造函数。

faint，裸灌：

class CString
{
public:
// Constructors

// constructs empty CString
CString();
// copy constructor
CString(const CString& stringSrc);
// from a single character
CString(TCHAR ch, int nRepeat = 1);
// from an ANSI string (converts to TCHAR)
CString(LPCSTR lpsz);
// from a UNICODE string (converts to TCHAR)
CString(LPCWSTR lpsz);
// subset of characters from an ANSI string (converts to TCHAR)
CString(LPCSTR lpch, int nLength);
// subset of characters from a UNICODE string (converts to TCHAR)
CString(LPCWSTR lpch, int nLength);
// from unsigned characters
CString(const unsigned char* psz);

// Attributes & Operations

// get data length
int GetLength() const;
// TRUE if zero length
BOOL IsEmpty() const;
// clear contents to empty
void Empty();

// return single character at zero-based index
TCHAR GetAt(int nIndex) const;
// return single character at zero-based index
TCHAR operator[](int nIndex) const;
// set a single character at zero-based index
void SetAt(int nIndex, TCHAR ch);
// return pointer to const string
operator LPCTSTR() const;

// overloaded assignment

// ref-counted copy from another CString
const CString& operator=(const CString& stringSrc);
// set string content to single character
const CString& operator=(TCHAR ch);
#ifdef _UNICODE
const CString& operator=(char ch);
#endif
// copy string content from ANSI string (converts to TCHAR)
const CString& operator=(LPCSTR lpsz);
// copy string content from UNICODE string (converts to TCHAR)
const CString& operator=(LPCWSTR lpsz);
// copy string content from unsigned chars
const CString& operator=(const unsigned char* psz);

// string concatenation

// concatenate from another CString
const CString& operator+=(const CString& string);

// concatenate a single character
const CString& operator+=(TCHAR ch);
#ifdef _UNICODE
// concatenate an ANSI character after converting it to TCHAR
const CString& operator+=(char ch);
#endif
// concatenate a UNICODE character after converting it to TCHAR
const CString& operator+=(LPCTSTR lpsz);

friend CString AFXAPI operator+(const CString& string1,
const CString& string2);
friend CString AFXAPI operator+(const CString& string, TCHAR ch);
friend CString AFXAPI operator+(TCHAR ch, const CString& string);
#ifdef _UNICODE
friend CString AFXAPI operator+(const CString& string, char ch);
friend CString AFXAPI operator+(char ch, const CString& string);
#endif
friend CString AFXAPI operator+(const CString& string, LPCTSTR lpsz);
friend CString AFXAPI operator+(LPCTSTR lpsz, const CString& string);

// string comparison

// straight character comparison
int Compare(LPCTSTR lpsz) const;
// compare ignoring case
int CompareNoCase(LPCTSTR lpsz) const;
// NLS aware comparison, case sensitive
int Collate(LPCTSTR lpsz) const;
// NLS aware comparison, case insensitive
int CollateNoCase(LPCTSTR lpsz) const;

// simple sub-string extraction

// return nCount characters starting at zero-based nFirst
CString Mid(int nFirst, int nCount) const;
// return all characters starting at zero-based nFirst
CString Mid(int nFirst) const;
// return first nCount characters in string
CString Left(int nCount) const;
// return nCount characters from end of string
CString Right(int nCount) const;

//  characters from beginning that are also in passed string
CString SpanIncluding(LPCTSTR lpszCharSet) const;
// characters from beginning that are not also in passed string
CString SpanExcluding(LPCTSTR lpszCharSet) const;

// upper/lower/reverse conversion

// NLS aware conversion to uppercase
void MakeUpper();
// NLS aware conversion to lowercase
void MakeLower();
// reverse string right-to-left
void MakeReverse();

// trimming whitespace (either side)

// remove whitespace starting from right edge
void TrimRight();
// remove whitespace starting from left side
void TrimLeft();

// trimming anything (either side)

// remove continuous occurrences of chTarget starting from right
void TrimRight(TCHAR chTarget);
// remove continuous occcurrences of characters in passed string,
// starting from right
void TrimRight(LPCTSTR lpszTargets);
// remove continuous occurrences of chTarget starting from left
void TrimLeft(TCHAR chTarget);
// remove continuous occcurrences of characters in
// passed string, starting from left
void TrimLeft(LPCTSTR lpszTargets);

// advanced manipulation

// replace occurrences of chOld with chNew
int Replace(TCHAR chOld, TCHAR chNew);
// replace occurrences of substring lpszOld with lpszNew;
// empty lpszNew removes instances of lpszOld
int Replace(LPCTSTR lpszOld, LPCTSTR lpszNew);
// remove occurrences of chRemove
int Remove(TCHAR chRemove);
// insert character at zero-based index; concatenates
// if index is past end of string
int Insert(int nIndex, TCHAR ch);
// insert substring at zero-based index; concatenates
// if index is past end of string
int Insert(int nIndex, LPCTSTR pstr);
// delete nCount characters starting at zero-based index
int Delete(int nIndex, int nCount = 1);

// searching

// find character starting at left, -1 if not found
int Find(TCHAR ch) const;
// find character starting at right
int ReverseFind(TCHAR ch) const;
// find character starting at zero-based index and going right
int Find(TCHAR ch, int nStart) const;
// find first instance of any character in passed string
int FindOneOf(LPCTSTR lpszCharSet) const;
// find first instance of substring
int Find(LPCTSTR lpszSub) const;
// find first instance of substring starting at zero-based index
int Find(LPCTSTR lpszSub, int nStart) const;

// simple formatting

// printf-like formatting using passed string
void AFX_CDECL Format(LPCTSTR lpszFormat, ...);
// printf-like formatting using referenced string resource
void AFX_CDECL Format(UINT nFormatID, ...);
// printf-like formatting using variable arguments parameter
void FormatV(LPCTSTR lpszFormat, va_list argList);

// formatting for localization (uses FormatMessage API)

// format using FormatMessage API on passed string
void AFX_CDECL FormatMessage(LPCTSTR lpszFormat, ...);
// format using FormatMessage API on referenced string resource
void AFX_CDECL FormatMessage(UINT nFormatID, ...);

// input and output
#ifdef _DEBUG
friend CDumpContext& AFXAPI operator<<(CDumpContext& dc,
const CString& string);
#endif
friend CArchive& AFXAPI operator<<(CArchive& ar, const CString& string);
friend CArchive& AFXAPI operator>>(CArchive& ar, CString& string);

// load from string resource
BOOL LoadString(UINT nID);

#ifndef _UNICODE
// ANSI <-> OEM support (convert string in place)

// convert string from ANSI to OEM in-place
void AnsiToOem();
// convert string from OEM to ANSI in-place
void OemToAnsi();
#endif

#ifndef _AFX_NO_BSTR_SUPPORT
// OLE BSTR support (use for OLE automation)

// return a BSTR initialized with this CString\'s data
BSTR AllocSysString() const;
// reallocates the passed BSTR, copies content of this CString to it
BSTR SetSysString(BSTR* pbstr) const;
#endif

// Access to string implementation buffer as \"C\" character array

// get pointer to modifiable buffer at least as long as nMinBufLength
LPTSTR GetBuffer(int nMinBufLength);
// release buffer, setting length to nNewLength (or to first nul if -1)
void ReleaseBuffer(int nNewLength = -1);
// get pointer to modifiable buffer exactly as long as nNewLength
LPTSTR GetBufferSetLength(int nNewLength);
// release memory allocated to but unused by string
void FreeExtra();

// Use LockBuffer/UnlockBuffer to turn refcounting off

// turn refcounting back on
LPTSTR LockBuffer();
// turn refcounting off
void UnlockBuffer();

// Implementation
public:
~CString();
int GetAllocLength() const;

protected:
LPTSTR m_pchData;   // pointer to ref counted string data

// implementation helpers
CStringData* GetData() const;
void Init();
void AllocCopy(CString& dest, int nCopyLen, int nCopyIndex, int nExtraLen) const;
void AllocBuffer(int nLen);
void AssignCopy(int nSrcLen, LPCTSTR lpszSrcData);
void ConcatCopy(int nSrc1Len, LPCTSTR lpszSrc1Data, int nSrc2Len, LPCTSTR lpszSrc2Data);
void ConcatInPlace(int nSrcLen, LPCTSTR lpszSrcData);
void CopyBeforeWrite();
void AllocBeforeWrite(int nLen);
void Release();
static void PASCAL Release(CStringData* pData);
static int PASCAL SafeStrlen(LPCTSTR lpsz);
static void FASTCALL FreeData(CStringData* pData);
};

楼上也太麻烦了，一句话就能讲明白吧！

都说了是裸灌嘛，呵呵