BUG REPORT: CStdioFile::GetLength() and unix-style text files

Not sure if this is the best place to report this or not. If we should be
sending this elsewhere, please notify and we'll do that.

We've discovered that when reading unix-style text files (i.e. files using
LF to terminate lines instead of CR LF), CStdioFile::GetLength() can cause
problems. Specifically, during the below read loop, the call to
CStdioFile::GetLength() appears to disturb the file pointer at times, causing
it to backup in the file to previously read content.

CStdioFile fp;
fp.Open("file",CFile::modeRead);
CString line;
while (fp.ReadString(line))
{
// do stuff with the read line
fp.GetLength();
}

For a sample file, we observed the above loop correctly reading the first 8
lines, however, when calling ReadString() to read the 9th line, it had backed
up to a place in the middle of the lines 2 lines prior. Interestingly, the
terminator (LF) for the 8th line happened to occur at offset 255 in the file.

Simply removing the call to CStdioFile::GetLength() eliminated the problem
and the entire file was read correctly.

If you examine the source for CStdioFile::GetLength(), you'll see it does
some seeking in the file. So apparently, this is causing problems.

The solution was to simply call CStdioFile::GetLength() only once,
immediately after the file was opened, before any reading was done. By
calling it only once and then just using that value in the loop (it was being
used to update a progress bar), the code works fine.

We're using MSVC++ 2005 SP1. The source we have in our install path for the
GetLength() method is shown below for reference.

---
ULONGLONG CStdioFile::GetLength() const
{
   ASSERT_VALID(this);

   LONG nCurrent;
   LONG nLength;
   LONG nResult;

   nCurrent = ftell(m_pStream);
   if (nCurrent == -1)
      AfxThrowFileException(CFileException::invalidFile, _doserrno,
         m_strFileName);

   nResult = fseek(m_pStream, 0, SEEK_END);
   if (nResult != 0)
      AfxThrowFileException(CFileException::badSeek, _doserrno,
         m_strFileName);

   nLength = ftell(m_pStream);
   if (nLength == -1)
      AfxThrowFileException(CFileException::invalidFile, _doserrno,
         m_strFileName);
   nResult = fseek(m_pStream, nCurrent, SEEK_SET);
   if (nResult != 0)
      AfxThrowFileException(CFileException::badSeek, _doserrno,
         m_strFileName);

   return nLength;
}