CFileException Class

Represents a file-related exception condition.

Syntax

class CFileException : public CException

Members

Public Constructors

Public Methods

Public Data Members

Remarks

The CFileException class includes public data members that hold the portable cause code and the operating-system-specific error number. The class also provides static member functions for throwing file exceptions and for returning cause codes for both operating-system errors and C run-time errors.

CFileException objects are constructed and thrown in CFile member functions and in member functions of derived classes. You can access these objects within the scope of a CATCH expression. For portability, use only the cause code to get the reason for an exception. For more information about exceptions, see the article Exception Handling (MFC).

Inheritance Hierarchy

CObject

CException

CFileException

Requirements

Header: afx.h

CFileException::CFileException

Constructs a CFileException object that stores the cause code and the operating-system code in the object.

CFileException(
    int cause = CFileException::none,
    LONG lOsError = -1,
    LPCTSTR lpszArchiveName = NULL);

Parameters

cause
An enumerated type variable that indicates the reason for the exception. See CFileException::m_cause for a list of the possible values.

lOsError
An operating-system-specific reason for the exception, if available. The lOsError parameter provides more information than cause does.

lpszArchiveName
Points to a string containing the name of the CFile object causing the exception.

Remarks

Don't use this constructor directly, but rather call the global function AfxThrowFileException.

CFileException::ErrnoToException

Converts a given run-time library error value to a CFileException enumerated error value.

static int PASCAL ErrnoToException(int nErrno);

Parameters

nErrno
An integer error code as defined in the run-time include file ERRNO.H.

Return Value

Enumerated value that corresponds to a given run-time library error value.

Remarks

See CFileException::m_cause for a list of the possible enumerated values.

Example

ASSERT(CFileException::ErrnoToException(EACCES) == 
   CFileException::accessDenied);

CFileException::GetErrorMessage

Retrieves text that describes an exception.

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

Parameters

lpszError
[in, out] Pointer to a buffer that receives an error message.

nMaxError
[in] The maximum number of characters the specified buffer can hold. This includes the terminating NULL character.

pnHelpContext
[in, out] Pointer to an unsigned integer that receives the help context ID. If NULL, no ID is returned.

Return Value

TRUE if the method was successful; otherwise FALSE.

Remarks

If the specified buffer is too small, the error message is truncated.

Example

The following example uses CFileException::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(_T("\\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();
}

CFileException::m_cause

Contains values defined by a CFileException enumerated type.

int m_cause;

Remarks

This data member is a public variable of type int. The enumerators and their meanings are as follows:

Example

try
{
   CFile f(_T("M_Cause_File.dat"), CFile::modeWrite);
}
catch(CFileException* e)
{
   if( e->m_cause == CFileException::fileNotFound)
      TRACE(_T("ERROR: File not found\n"));
   e->Delete();
}

CFileException::m_lOsError

Contains the operating-system error code for this exception.

LONG m_lOsError;

Remarks

See your operating-system technical manual for a listing of error codes. This data member is a public variable of type LONG.

CFileException::m_strFileName

Contains the name of the file for this exception condition.

CString m_strFileName;

CFileException::OsErrorToException

Returns an enumerator that corresponds to a given lOsError value. If the error code is unknown, then the function returns CFileException::generic.

static int PASCAL OsErrorToException(LONG lOsError);

Parameters

lOsError
An operating-system-specific error code.

Return Value

Enumerated value that corresponds to a given operating-system error value.

Example

ASSERT(CFileException::OsErrorToException(ERROR_ACCESS_DENIED) == 
   CFileException::accessDenied);

CFileException::ThrowErrno

Constructs a CFileException object corresponding to a given nErrno value, then throws the exception.

static void PASCAL ThrowErrno(int nErrno, LPCTSTR lpszFileName = NULL);

Parameters

nErrno
An integer error code as defined in the run-time include file ERRNO.H.

lpszFileName
A pointer to the string containing the name of the file that caused the exception, if available.

Example

CFileException::ThrowErrno(EACCES);  // "access denied"

CFileException::ThrowOsError

Throws a CFileException corresponding to a given lOsError value. If the error code is unknown, then the function throws an exception coded as CFileException::generic.

static void PASCAL ThrowOsError(LONG lOsError, LPCTSTR lpszFileName = NULL);

Parameters

lOsError
An operating-system-specific error code.

lpszFileName
A pointer to the string containing the name of the file that caused the exception, if available.

Example

CFileException::ThrowOsError(ERROR_ACCESS_DENIED);  // "access denied"         

See also

CException Class
Hierarchy Chart
Exception Processing