CException

MFC Library Reference
CException::GetErrorMessage
 
Call this member function to provide text about an error that has occurred.

virtual BOOL GetErrorMessage(
 LPTSTR lpszError,
 UINT nMaxError,
 PUINT pnHelpContext = NULL 
);

Parameters

lpszError
A pointer to a buffer that will receive an error message.
nMaxError
The maximum number of characters the buffer can hold, including the NULL terminator.
pnHelpContext
The address of a UINT that will receive the help context ID. If NULL, no ID will be returned.
 Return Value
Nonzero if the function is successful; otherwise 0 if no error message text is available.
 Remarks
For example, call GetErrorMessage to retrieve a string describing the error which caused MFC to throw a CFileException when writing to a CFile object.
Note
GetErrorMessage will not copy more than nMaxError -1 characters to the buffer, and it will always add a trailing null to end the string. If the buffer is too small, the error message may be truncated.
 Example
Here is an example of the use of CException::GetErrorMessage.

CFile fileInput;
 CFileException ex;

 // try to open a file for reading.
 // The file will certainly not
 // exist because there are too many explicit
 // directories in the name.

 // if the call to Open() fails, ex will be
 // initialized with exception
 // information. the call to ex.GetErrorMessage()
 // will retrieve an appropriate message describing
 // the error, and we'll add our own text
 // to make sure the user is perfectly sure what
 // went wrong.

 if (!fileInput.Open("//Too//Many//Bad//Dirs.DAT", CFile::modeRead, &ex))
 {
 TCHAR szCause[255];
 CString strFormatted;

 ex.GetErrorMessage(szCause, 255);

 // (in real life, it's probably more
 // appropriate to read this from
 // a string resource so it would be easy to
 // localize)

 strFormatted = _T("The data file could not be opened because of this error: ");
 strFormatted += szCause;

 AfxMessageBox(strFormatted);
 }
 else
 {
 // the file was opened, so do whatever work
 // with fileInput
 // we were planning...
 // :

 fileInput.Close();
 }