🚀 go-pugleaf

"DP" <ramneek_devinder@comcast.net> schrieb im Newsbeitrag
news:Xns94795E615C598ramneekdevindercomca@207.105.83.66...
> Hi,
>   How do I Lock a file so that second user trying to open the file is just
> able to read the contents. The first user needs to be able to read and
> write both.
>    I have been trying to play with CreateFile API and its flags and
somehow
> it seems to fail when an attempt is made to open a same file across the
> network by two users.
>

I prefer to use TFileStream.

On first machine/process:

 // the file must already exists
 // if not, it must be created
 // be carefull with fmCreate!
 // if you use fmCreate then share-attributes will ingored [1]

 // others may read the file, but they are not allowed to write
 fs := TFileStream('\\fileserver\directory\test.txt', fmOpenReadWrite or
fmShareDenyWrite);


On the other machines:
 // open the file for reading, others are allowed to read and write
 fs := TFileStream('\\fileserver\directory\test.txt', fmOpenRead or
fmShareDenyNone);

-----------------------------------------------------

[1]
internally, a call to FileCreate will be made:

The FileCreate function doesn't have a "mode" parameter,
so it isn't possible to pass Shared-Flags in.

function FileCreate(const FileName: string): Integer;
begin
  Result := Integer(CreateFile(PChar(FileName), GENERIC_READ or
GENERIC_WRITE,
    0, nil, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0));
end;

// revised code (this is how Borland should have made it)
function FileCreate(const FileName: string; Mode: LongWord): Integer;
const
  ShareMode: array[0..4] of LongWord = (
    0,
    0,
    FILE_SHARE_READ,
    FILE_SHARE_WRITE,
    FILE_SHARE_READ or FILE_SHARE_WRITE);
begin
  Result := Integer(CreateFile(PChar(FileName), GENERIC_READ or
GENERIC_WRITE,
    ShareMode[(Mode and $F0) shr 4], nil, CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL, 0));
end;



hth
Andreas