Title: How to get a file size algorithmic way
Question: In article http://www.delphi3000.com/articles/article_2351.asp by Adam Lanzafame shows how to use windows api to format a file size using api in this article I show how to do it using algorithm
Answer:
In the article mentioned above you get a way to format a filesize by using windows api, however these haves its drawbacks, just to name the most interesting, take a look at how rounding works that way if a file is 14.569 KB windows will round it to 14.56 KB instead of 14.57 KB, why? I dont know it and this article seeks not to discuss it however here is a function wich does the same formatting while avoiding the mentioned rounding problem:
function GetAFileSize(SizeInBytes: Integer): String;
const
Preffixes: array[0..3] of String = //Common file sizes preffixes
(' Bytes', ' KB', 'MB', ' GB'); //Change if you want to anything that suits
FormatSpecifier: array[Boolean] of String =
('%n', '%.2n'); //the way we format the string;
var
i: integer; //A counter
TmpSize: Real; //A temporary variable
begin
i := -1; //Avoid compiler complain
tmpSize := SizeInBytes; //Avoid compiler complain
while (i // a file will rarely pass a GB up to 3
begin
TmpSize := TmpSize / 1024; //1 MB = 1024 KB, 1 KB = 1024 Bytes, 1 Byte = 8 Bits, 1 bit = nothing
inc( i ); //increment counter and select preffix string
if Trunc( TmpSize )= 0 then //we reached a maximum nuber of divisions so
begin
TmpSize := TmpSize * 1024; //Tmpsize was divided 1 time more than necessary
Break; //Exit of loop;
end;
end;
//Actual formatting routine
Result := Format(FormatSpecifier[((Frac(TmpSize)*10) 1)], [TmpSize]) + Preffixes[i];
end;
Notes of interest:
* These algorithm relies on delphi native format function, wich kind of limits it
* It isnot part of windows api, you have to copy and paste it whenever you use it
* Unlike windows api it has correct rounding and can be extended
This compact function with a couple of changes could be used as a export function in a dll, as a matter of fact here is some code wich "serves this purpose"
function MYStrFormatByteSizeA(dwSize: Integer; pszBuf: PChar; cchBuffsize: integer): PChar;
const
Preffixes: array[0..3] of PChar = (' Bytes', ' KB', 'MB', ' GB');
FormatSpecifier: array[Boolean] of PChar = ('%n', '%.2n');
var
i: integer;
TmpSize: Real;
TmpResult: PChar;
begin
i := -1;
tmpSize := dwSize;
while (i begin
TmpSize := TmpSize / 1024;
inc( i );
if Trunc( TmpSize )= 0 then
begin
TmpSize := TmpSize * 1024;
Break;
end;
end;
// Since working with PChars here have to think PChar
StrFmt( TmpResult, FormatSpecifier[((Frac(TmpSize)*10) 1)], [TmpSize] );
StrCat( TmpResult, Preffixes[i] );
Result := TmpResult;
end;
An example to use any of the functions above:
function getfilesizeex(AFilename: string): String;
//must include complete filepath
var ASR: TSearchRec;
Size: Integer;
begin
FindFirst(AFileName, faArchive, ASR);
Size := ASR.FindData.nFilesizeHigh * MaxDWord + ASR.FindData.nFileSizeLow
Result := GetAFileSize( Size );
FindClose( ASR );
end;
Truly yours
The Object Pascal guy