Re: Searching for byte sequence

"Kahlua" <>
Tue, 22 Apr 2008 15:00:11 GMT
Thanks for all this usefull/informative information.
The files I am reading into buffer contain both text and binary data in
I need to search for a text string and move the position ahead to the binary
data that follows.
Then I need to extract a known number of bytes to another buffer for
After the binary data is text again which I need to search again for a
certain string.
Thanks for the help.

"Joseph M. Newcomer" <> wrote in message

See below...
On Tue, 22 Apr 2008 13:24:32 GMT, "Kahlua" <> wrote:

I have a ListBox with a list of files in the c:\data\ folder with the
extension .dat
Now that I have the file coppied into buffer how do I search through the
for a specific sequence of bytes?


void CMyApp::OnSelchangeList()
 CString mess;
 CString JobFile;
 char cSelect[50];

at the VERY least. Better still,

CString cSelect;

 int Length;
 int nSelect;
 CByteArray buffer;
 CFile in;

 nSelect=SendDlgItemMessage(IDC_LIST, LB_GETCURSEL, 0, 0L);

Why such a crude and antiquated mechanism? Create a control variable for
your list and do
    nSelect = c_List.GetCurSel();
note how much easier it is!

 DlgDirSelect((LPSTR) cSelect, IDC_LIST);

Note that DlgDirSelect makes the GetCurSel superfluous, but actually the
simplest thing to
do is to write
   c_List.GetText(nSelect, cSelect);
which is a whole lot easier

 if (cSelect[Length-1]==0x2e)

I can't figure out what this is doing because I have no idea what the
purpose of it is.
For example, what in the world is 0x2e? Perhaps you meant to write
   if(cSelect[Length-1] == _T(','))

If you are testing for a character, it is generally considered good
programming practice
to use the character, and not its hex equivalent.

Also, using the obsolete 'char' data type is not good programming
practice; you should get
the length by writing
Length = _tcslen(cSelect);

But note that this is much more readily written if you have a CString:
    if(cSelect.Right(1) == _T("."))
        cSelect = cSelect.Left(cSelect.GetLength() - 1);
which is a lot easier to write and understand. Note that you don't need
to get the length
as a separate variable.

 JobFile = _T("c:\\data\\");

You are correctly using _T() here, but in a Unicode build the next line
would fail

 JobFile += cSelect;
 JobFile += ".dat";

So why did you use _T() in one literal but not in another?

 mess = "Would you like to load ";
 mess += cSelect;
 mess += " as top ?";

This would be a lot easier to write as
   CString mess;
   mess.Format(_T("Would you like to load \"%s\" as top ?"), cSelect);

Note that you do not need to declare the variable at the top; you do not
need to declare
it until it is actually needed. Better still, put that string in the
it, so you can localize

 int a = MessageBox (mess, "Query", MB_ICONINFORMATION|MB_YESNO);

int a = AfxMessageBox(mess, MB_ICONQUESTION | MB_YESNO);

It is NOT an information prompt, it is a question prompt. Use
AfxMessageBox, which
follows recommended best practice for the caption (uses the program name).
Use white
space around binary operators to make them legible

 if (a==IDNO) return;

It would be safer to say
   if(a != IDYES)

This tests for the actual meaningful value; note the whitespace around the
operator; note
that it uses two lines, which makes it easier to debug.

 if(!in.Open(JobFile, CFile::modeRead)){
   DWORD err = ::GetLastError();
   CString msg;
   msg.Format(_T("Error opening file: %d"), err);
 if((INT_PTR)in.Read(buffer.GetData(), buffer.GetSize()) !=
   DWORD err = ::GetLastError();
   CString msg;
   msg.Format(_T("Error reading file: %d"), err);

Are you searching for text or a binary pattern not expressible as text?
If this is text,
and is known to be 8-bit characters, always, one solution is
    CStringA buffer;
    LPSTR p = buffer.GetBuffer(in.GetLength());
    if((INT_PTR)in.Read(p, in.GetLength()) != in.GetLength())
      ... as above

   int n = buffer.Find("abc");
   if(n < 0)
     ...not found

If you need to find all instances of an 8-bit character string, you would
have a loop, and
the second parameter of Find would give the starting offset for the next

However, if your file is in UTF-8 encoding, you would have to use the
UTF-8 representation
of the string (the most efficient means) or convert the file to a Unicode
(not efficient for large files, especially if the string ends up not being
found). If
your file is potentially Unicode, life gets a good deal more complex, but
I don't want to
get into that here right now.


Joseph M. Newcomer [MVP]
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