Delphi Tutorial: Obtain the correct file
size with TWin32FindData.
Introduction
This short tutorial explains how to use obtain the correct
file size from the TsearchRec.FindData structure for files that are larger than
2GB.
TSearchRec
Delphi lets you use FindFirst and FindNext to obtain
information about files. If the file was found, FindFirst returns a zero and
places file information into a TSearchRec record which has the following
structure:
TSearchRec = record
Time:
Integer; // time of last modification
Size:
Integer; // file size
Attr:
Integer; // file
attributes
Name:
TFileName; // file name
ExcludeAttr:
Integer;
FindHandle:
THandle;
FindData:
TWin32FindData; // Win32_FIND_DATA
structure
end;
Size contains the size of the file in bytes – at
least that is what it says in Delphi’s help. Unfortunately if the file is
greater than 2 Gigabytes, size will yield the incorrect size. The good news is
that you can still obtain the correct file size from TSearchRec using
TSearchRec.FindData.
TsearchRec.FindData corresponds to the WIN32_FIND_DATA structure used in the Win32
FindFirstFile and FindNextFile API functions. It is defined as follows:
TWin32FindData structure.
|
type
PWin32FindDataA
= ^TWin32FindDataA;
PWin32FindDataW
= ^TWin32FindDataW;
PWin32FindData
= PWin32FindDataA;
_WIN32_FIND_DATAA = record
dwFileAttributes: DWORD; // file attributes
ftCreationTime: TFileTime; // Created date and
time
ftLastAccessTime: TFileTime; // Last accessed date
and time
ftLastWriteTime: TFileTime; // Modified date and
time
nFileSizeHigh: DWORD; // file size
high word
nFileSizeLow:
DWORD; //
file size low word
dwReserved0:
DWORD; //
reserved for future use
dwReserved1:
DWORD; //
reserved
cFileName:
array[0..MAX_PATH - 1] of AnsiChar;
// full file name
cAlternateFileName: array[0..13] of AnsiChar; // alternate (short) file name
end;
|
Obtaining the correct file size.
The
file size in this structure is defined by nFileSizeHigh and nFileSizeLow. You
can convert this to an Int64 value using the formula:
FileSize
= nFileSizeHigh shl 32 + nFileSizeLow
To
ensure the correct result, you must explicitly typecast all variables and
values in the expression as Int64. The following function uses FindFirst to
obtain the exact file size from the FindData structure.
|
// return the exact file size for a file. Return zero
if the file is not found.
Function FileSize(FileName : String) : Int64;
var
SearchRec :
TSearchRec;
begin
if
FindFirst(FileName, faAnyFile, SearchRec ) = 0 then // if found
Result :=
Int64(SearchRec.FindData.nFileSizeHigh) shl Int64(32) + // calculate the size
Int64(SearchREc.FindData.nFileSizeLow)
else
Result := 0;
FindClose(SearchRec);
// close the find
end;
|
|
Delphi 6 online help
|
See: FindFirst, FindNext, TSearchRec
|
|
WIN32.HLP
|
The Microsoft Win32 Programmers Reference
|
|
Windows.pas
|
Borland Delphi Run-time Library - Win32 API Interface
Unit.
|
Books
The
Tomes of Delphi: Win32 Core API - Windows 2000
Edition by John Ayers, ISBN 1-55622-750-7 Wordware Publishing Inc
The
Tomes of Delphi: Win32 Shell API – Windows
2000 Edition by John Ayers, ISBN 1-55622-749-3 Wordware Publishing
Inc
Windows
2000 SYSTEMS PROGRAMMING Black Book by Al Williams, 2000, ISBN 1-57610-280-7, The
Coriolis Group
Misc.
Use
of Source Code
The source code contained in this tutorial is provided free of charge,
AS IS WITHOUT WARRANTY OF ANY KIND AND IS PROVIDED WITHOUT ANY IMPLIED WARRANTY
OF FITNESS FOR PURPOSE OR MERCHANTABILITY. You may incorporate this source code
into your own program but you do so at your own risk. Please remember to test
your program and any source code copied from this site. Please report errors
and improvements to jpgriffiths.com.
Copyright © 2002 - 2006 Paul Griffiths, www.jpgriffiths.com.
Last
Update
Last Updated: [May, 2006]
Achknowledgement
Special thanks to Pierre R for correcting an error in the FileSize
example.
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