single file size limitation?

Hello All...
   Is anyone aware of a single file size limitation for opening/reading a file in a Delphi app? I'm testing my app on Win 2000 and XP and it works correctly on reading and processing large files of up to around 4 gigs in size. Over and above that, it gives incorrect and wacky results (the results consistemtly show as a much smaller number than expected)... like some internal counter has been exceeded.

  I seem to be able to correctly process several files whose TOTAL exceeds 4 gigs, no problem... as long as each of those files are less than 4 gigs. But as soon as any one single file exceeds 4 gigs, something gets blown. Don't know whether to think this is an operating system limitation, or a Delphi limitation.

I'm using D3 Professional.

Who is Participating?
CynnaConnect With a Mentor Commented:

This free component (with source) enables you
to work with 64-bit file sizes:

This is not a Delphi problem at all. The size limit of 4 Gig (2 Gig for FAT file systems) stems from the simple fact that the size is stored in a DWORD. It is a limit of many file systems.
aztecAuthor Commented:
I see... but my app can create OUTPUT files of sizes greater than 4 gigs...

How can this be?
Free Tool: ZipGrep

ZipGrep is a utility that can list and search zip (.war, .ear, .jar, etc) archives for text patterns, without the need to extract the archive's contents.

One of a set of tools we're offering as a way to say thank you for being a part of the community.

Then it simply may be that your program eats up 1000 % CPU. Show your code.
aztecAuthor Commented:
1000% ??

you mean 100%? How could using 100% of CPU result in a limitation of the file sizes I can read in?
Sorry, posted to the wrong question.

NTFS does not have the size limit, but as long as you use the file functions with DWORD for position or size parameters you will be lost in your file. Sequential reading and writing works, but repositioning should be modulo 4 Gigs.
aztecAuthor Commented:
ok, no problem!

Well, I am using 'BlockRead' to read in the data file. Maybe this could be the problem? If I switch to using maybe TFileStream instead it might solve this?
  Below is my code when I read in the file:

var buf : array[0..49151] of char;
    fromfile : file;

   blockread(fromfile, buf, 1, numread);
   recsread:=recsread + 1;
   for z:=0 to 49151 do
     if ((ord(buf[z])>= 0) and (ord(buf[z]) <= 31)) or
        ((ord(buf[z])>= 127) and (ord(buf[z]) <= 255))  then
        if bigstring <> '' then find_valid;
       bigstring:=concat(bigstring, buf[z]);
       if length(bigstring) = 255 then find_valid;

   bytes_processed:=bytes_processed + 49152;
   if recsread mod 10 = 0 then
     hperc:=calc_status(totsizeoffile, bytes_processed);

 until EOF(fromfile);

You should revert to Win32 API. The function family CreateFile, ReadFiel, WriteFile also contains functions for file size and seeking (GetFileSizeEx and SetFilePointerEx) which use Int64 to overcome the DWORD limit.
aztecAuthor Commented:
So TFileStream wouldn't help?

OK, how do I use these Win32 API file commands? Would you have some samples?

Are they faster/more efficient for reading/writing than the regular Read/Write statements for text files?
aztecAuthor Commented:
I see nothing for these commands in the Delphi 3 Help file...
Get the Platform SDK from Microsoft. It contains all the help you need. The Delphi help is outdated because they have to license it from MS.

CreateFile ReadFile etc are the core functions for files. All Delphi functions have to base on them.
aztecAuthor Commented:
can I download this somewhere? Is it free?
Yes, go to and search for "Platform SDK".
aztecAuthor Commented:
Robert - does the "Readfile" from the Platform SDK let you do like a "Readln"? Where it will read in one full line (ended by a CR/LF) at a time (without having to specify byte-count)? I am reading in text-files like this and this is essential for me.

Cynna - thanks for the component suggestion. But when I try to install it, it gives a compile error in the "GPHugeF" file - File Not Found "SysConst.dcu". I am using Delphi 3 Pro. Maybe I don't have this file?
  Also, will this component address the issues I mention aboe to Robert?

aztecAuthor Commented:
Also Robert - there is like 7 different components of the Platform SDK... do I need them all, or is there only a specific one I need to install?
It is always wise to have all possible help available.
ReadFile does not allow to read lines.
aztecAuthor Commented:
So can I do this then? How can I read text files > 4 gigs in a line by line fashion?
1. Rethink your strategy. >4 Gigs line by line will take ages. Having unstructured textual information of that size indicates poor design.
2. Write a simple class with a big buffer where you pick the lines from. That is basic programming technique.
aztecAuthor Commented:
(1) But this is the structure of my data. Large files consisting of one email address on each line - which I must read in and process one at a time. I cannot change this.

(2) How do I do this and just pick out 1 address/line at a time (ie. up to the first CR/LF) ?

> File Not Found "SysConst.dcu"

Well, D3 obviously doesn't have this unit. Try this:

1. Copy this to NotePad:

unit SysConst;


  SUnknown = '<unknown>';
  SInvalidInteger = '''%s'' is not a valid integer value';
  SInvalidFloat = '''%s'' is not a valid floating point value';
  SInvalidDate = '''%s'' is not a valid date';
  SInvalidTime = '''%s'' is not a valid time';
  SInvalidDateTime = '''%s'' is not a valid date and time';
  STimeEncodeError = 'Invalid argument to time encode';
  SDateEncodeError = 'Invalid argument to date encode';
  SOutOfMemory = 'Out of memory';
  SInOutError = 'I/O error %d';
  SFileNotFound = 'File not found';
  SInvalidFilename = 'Invalid filename';
  STooManyOpenFiles = 'Too many open files';
  SAccessDenied = 'File access denied';
  SEndOfFile = 'Read beyond end of file';
  SDiskFull = 'Disk full';
  SInvalidInput = 'Invalid numeric input';
  SDivByZero = 'Division by zero';
  SRangeError = 'Range check error';
  SIntOverflow = 'Integer overflow';
  SInvalidOp = 'Invalid floating point operation';
  SZeroDivide = 'Floating point division by zero';
  SOverflow = 'Floating point overflow';
  SUnderflow = 'Floating point underflow';
  SInvalidPointer = 'Invalid pointer operation';
  SInvalidCast = 'Invalid class typecast';
  SAccessViolation = 'Access violation at address %p. %s of address %p';
  SStackOverflow = 'Stack overflow';
  SControlC = 'Control-C hit';
  SPrivilege = 'Privileged instruction';
  SOperationAborted = 'Operation aborted';
  SException = 'Exception %s in module %s at %p.'#$0A'%s%s';
  SExceptTitle = 'Application Error';
  SInvalidFormat = 'Format ''%s'' invalid or incompatible with argument';
  SArgumentMissing = 'No argument for format ''%s''';
  SInvalidVarCast = 'Invalid variant type conversion';
  SInvalidVarOp = 'Invalid variant operation';
  SDispatchError = 'Variant method calls not supported';
  SReadAccess = 'Read';
  SWriteAccess = 'Write';
  SResultTooLong = 'Format result longer than 4096 characters';
  SFormatTooLong = 'Format string too long';
  SVarArrayCreate = 'Error creating variant array';
  SVarNotArray = 'Variant is not an array';
  SVarArrayBounds = 'Variant array index out of bounds';
  SExternalException = 'External exception %x';
  SAssertionFailed = 'Assertion failed';
  SIntfCastError = 'Interface not supported';
  SSafecallException = 'Exception in safecall method';
  SAssertError = '%s (%s, line %d)';
  SAbstractError = 'Abstract Error';
  SModuleAccessViolation = 'Access violation at address %p in module ''%s''. %s of address %p';
  SCannotReadPackageInfo = 'Cannot access package information for package ''%s''';
  sErrorLoadingPackage = 'Can''t load package %s.'#13#10'%s';
  SInvalidPackageFile = 'Invalid package file ''%s''';
  SInvalidPackageHandle = 'Invalid package handle';
  SDuplicatePackageUnit = 'Cannot load package ''%s.''  It contains unit ''%s,''' +
    ';which is also contained in package ''%s''';
  SWin32Error = 'Win32 Error.  Code: %d.'#10'%s';
  SUnkWin32Error = 'A Win32 API function failed';
  SNL = 'Application is not licensed to use this feature';

  SShortMonthNameJan = 'Jan';
  SShortMonthNameFeb = 'Feb';
  SShortMonthNameMar = 'Mar';
  SShortMonthNameApr = 'Apr';
  SShortMonthNameMay = 'May';
  SShortMonthNameJun = 'Jun';
  SShortMonthNameJul = 'Jul';
  SShortMonthNameAug = 'Aug';
  SShortMonthNameSep = 'Sep';
  SShortMonthNameOct = 'Oct';
  SShortMonthNameNov = 'Nov';
  SShortMonthNameDec = 'Dec';

  SLongMonthNameJan = 'January';
  SLongMonthNameFeb = 'February';
  SLongMonthNameMar = 'March';
  SLongMonthNameApr = 'April';
  SLongMonthNameMay = 'May';
  SLongMonthNameJun = 'June';
  SLongMonthNameJul = 'July';
  SLongMonthNameAug = 'August';
  SLongMonthNameSep = 'September';
  SLongMonthNameOct = 'October';
  SLongMonthNameNov = 'November';
  SLongMonthNameDec = 'December';

  SShortDayNameSun = 'Sun';
  SShortDayNameMon = 'Mon';
  SShortDayNameTue = 'Tue';
  SShortDayNameWed = 'Wed';
  SShortDayNameThu = 'Thu';
  SShortDayNameFri = 'Fri';
  SShortDayNameSat = 'Sat';

  SLongDayNameSun = 'Sunday';
  SLongDayNameMon = 'Monday';
  SLongDayNameTue = 'Tuesday';
  SLongDayNameWed = 'Wednesday';
  SLongDayNameThu = 'Thursday';
  SLongDayNameFri = 'Friday';
  SLongDayNameSat = 'Saturday';



2. Save that text as 'sysconst.pas' in the same folder
   you extracted GpHugeF.pas

3. Now it should compile OK.

>Also, will this component address the issues I mention aboe to Robert?

Yes it will.

> (2) How do I do this and just pick out 1 address/line at a time (ie. up to the first CR/LF) ?

Use BlockRead method of TGpHugeFile to read file chunk by chunk, and search for CR/LF inside every chunk.
aztecAuthor Commented:
ok Cynna, thanks.

For fastest file reading, what do you recommend as an efficient 'chunk-size'? 2 megs? 4 megs?


Well generally, the more - the better. It depends on
your target system average expected free mem.
For example, I'd use 8Mb as a start point on my system...

Anyway, you could very easily change several values and
measure how it impacts your performance, so you could
make best judgement for yourself.
aztecAuthor Commented:
OK Cynna, I did what you suggested for the sysconst.pas, now when installing the HugeFile component, I get a new error on this linein the GPHugeF.pas file:

  start : int64

"Error: Undeclared identifier: 'int64'"

Any suggestions? I am using Delphi 3 Pro.


D3 - well that's a kind of a problem...
Int64 wasn't introduced until D4, I think.

You might try replacing Int64 with Comp. But the
problem might be that Comp is float, while Int64 is
(surprise, surprise...) integer. This can create
problems if GPHugeF.pas uses operations like div
(specific to integers) on Int64 types. You might
try tweeking this code a bit, if you get any other

Other then that I'm afraid I can't think of anything
simple, considering your platform. Additional problem
is I have D5, and can't really test D3 specific code....

If you get stuck again, post it, and I'll try helping you
a bit later.
aztecAuthor Commented:
Thanks for the suggestion Cynna. I made the change of int64 to comp (for 2 variables - start and stop), but it gave a new compile error for this line:

stop := stop + $100000000;

"Integer expression too large"

Plus there were other compile errors everywhere "Win32Check" was mentioned. :-(

Am I stuck? Is it possible to email directly the creator of this component?
Well, aztec, you're pretty close to beeing stuck, as far as I can see...

But, try one more final idea:

procedure TForm1.Button1Click(Sender: TObject); // read file
const  cBufSize = 2048;
var Buffer   : Array [0..cBufSize] of Char;
    hRead    : THandle;
    FileName : String;
    read     : DWORD;
   // Ensure our Buffer is always zero-terminated:
   // Place your full file name here:
   hRead := CreateFile( PChar(FileName),
                        FILE_SHARE_READ or FILE_SHARE_WRITE,
                        0 );
   while ReadFile(hRead, Buffer, cBufSize, read, nil) do begin
         // ----------- Process Buffer: ------------------
         // .... your block-parsing code here ...
         // ----------------------------------------------
         Memo1.Text:=StrPas(Buffer); // just a demo
         Application.ProcessMessages; Sleep(1);
         if read<cBufSize then Break;
   // Final block processing:
   // ----------- Process Buffer: ------------------
   // .... your block-parsing code here ...
   // ----------------------------------------------
   Memo1.Text:=StrPas(Buffer); // just a demo

This code uses WinAPI native file handling operations.
It relies on sequential read, so it doesn't touch
your D3 limitation.
I used it just as a demo. You should use your large
file name in var FileName.
If you see the end of your large file in Memo1, when it
finishes, it works OK. If it works OK, write your block
parsing code instead of Memo1.Text:=... part and you're done.
If it doesn't, I'm afraid I'm all out of quick-ideas for this one...

Good luck!

aztecAuthor Commented:
Thanks Cynna - I just went ahead and upgraded to the D6 Personal Edition ...everything works fine now!

(thanks for the final D3 suggestion however!)

> ..I just went ahead and upgraded to the D6 Personal Edition...

Smart move.
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

All Courses

From novice to tech pro — start learning today.