Unexpected AfxThrowFileException in CStdioFile::Read()

Question

I am using CStdioFile::Read in an MFC application, and I noticed that an exception is thrown in the following condition:

if ((nRead = (UINT)fread(lpBuf, sizeof(BYTE), nCount, m_pStream)) == 0 && !feof(m_pStream))         AfxThrowFileException(CFileException::genericException, _doserrno, m_strFileName);

I understand that nRead == 0 means no bytes were read, but since feof(m_pStream) is false, it suggests that EOF has not been reached.

Also, before calling CStdioFile::Read, we have checked that the file is open using CStdioFile::Open function too.

Below is the sample code :

static bool ReadIniFile(
    const CString& cstrIniFilePath,   
    std::map<CString, CString>& IniMap
)
{
    bool bRet = false;
    CStdioFile cFile;
    UINT TextMode = CFile::modeRead | CFile::typeText | CFile::shareDenyNone;
 
    IniMap.clear();
 
    if (cFile.Open(cstrIniFilePath, CFile::modeRead | CFile::typeBinary | CFile::shareDenyNone))   
    {
        BYTE cBuf[16];
        if ((cFile.Read(cBuf, 2) == 2) && (cBuf[0] == 0xFF) && (cBuf[1] == 0xFE)) // Crash point
        {
            TextMode = CFile::modeRead | CFile::typeUnicode | CFile::shareDenyNone;
        }
        cFile.Close();
 
        if(cFile.Open(cstrIniFilePath, TextMode))
        {
            if ((TextMode & CFile::typeUnicode) != 0)
            {
                cFile.Seek(2, CFile::begin);
            }
 
            CString strLine;
            CString strSection;
            CString strKey;
            CString strValue;
            while(cFile.ReadString(strLine))
            {
                strLine.Trim();
                int len = strLine.GetLength();
                if(len > 2)
                {
                    if(strLine[0] == '[')
                    {
                        int n = strLine.Find(']');
                        if(n >= 2)
                        {
                            strSection = strLine.Mid(1, (n - 1));
                        }
                    }
                    else if(!strSection.IsEmpty())
                    {
                        int n = strLine.Find('=');
                        if((n > 0) && ((n + 1) < len))
                        {
                            strKey = strLine.Left(n);
                            strKey.TrimRight();
                            strValue = strLine.Mid(n + 1, len - n);
                            strValue.TrimLeft();
 
                            CString strMapKey = strSection + _T("&") + strKey;
                            strMapKey.MakeUpper();
                            strValue.Replace(_T("\\n"), _T("\n"));
                            auto itr = IniMap.find(strMapKey);
                            if(itr == IniMap.end())
                            {
                                IniMap[strMapKey] = strValue;
                            }
                        }
                    }
                }
            }
            cFile.Close();
            bRet = true;
        }
    }
    return bRet;
}

Here file seems valid and not corrupted.

Question:

What are the possible reasons for this exception to be triggered?

• Could this be due to file permissions, locking, or disk errors?
• Are there any specific scenarios where fread fails but feof remains false?
• How should I handle this exception properly to differentiate between different failure scenarios?