Read returning 0 has nothing (read should have nothing) to do with you
buffer memory allocation.
It is more likely it has failed to open the file on disk, or has actually
reached the EOF.
However for these purposes I do it this way.
var
Buffer: array [0..MaxBuf] of Char; {Compatible with PChar, MaxBuf being
the maximum to read at any one time}
MyPChar: PChar;
...
if Read( Buffer, 1 ) = 0 then ...
or
MyPChar := @Buffer
if Read( MyPChar^, 1) = 0 then ...
This has the advantage that the buffer is allocated on stack instead of on
the Heap.
Myles.
> -----Original Message-----
> From: Carl Reynolds [SMTP:[EMAIL PROTECTED]]
> Sent: Friday, August 06, 1999 12:13 PM
> To: Multiple recipients of list delphi
> Subject: Strings, PChars, and TFileStream.Read
>
> Hi all. I thought it was safe to use PChar(MyString) in Delphi 4 whenever
> you needed a PChar, but I'm having a problem with the following code
> (somewhat simplified):
>
> var LChar: string;
> begin
> with TFileStream.Create(ParamStr(0), // Any file will do - this is
> just one guaranteed to exist
> fmOpenRead or fmShareDenyNone) do try
> LChar := 'X';
> if Read(PChar(LChar)^, 1) = 0 then begin
> ShowMessage('Say what?!!');
> end
> else ShowMessage('Whew!');
> finally
> Free;
> end;
> end;
>
> In some cases, depending on what other code I've got in unrelated places,
> I get 0 returned - ie., the TFileStream thinks that it can't read from the
> file or that the file is empty, which obviously should never be the case.
> Things are complicated by the fact that the error rarely happens, and when
> it does putting in a ShowMessage or a breakpoint cause it to _not_ happen!
>
> So what I'm really asking is, is the code safe? Should I do one of the
> following, which all seem to work (but do they really - for all cases?):
>
> 1/.
> ...
> LChar := 'X';
> UniqueString(LChar); // Is this really necessary?
> ...
>
> 2/.
> ...
> SetLength(LChar, 1); // Should I be more explicit about
> memory allocation?
> ...
>
> 3/.
> ...
> var LChar: string;
> LPChar: PChar;
> <snip>
> LChar := 'X';
> LPChar := PChar(LChar); // Or is this a safer way to do it?
> if Read(LPChar)^, 1) = 0 then begin
> ...
>
> Or can't I mix PChars and strings at all?
>
> ...
> var LPChar: PChar;
> <snip>
> StrAlloc(LPChar, 1);
> if Read(LPChar)^, 1) = 0 then begin
> ...
>
> Explanations for any of this gratefully received.
>
> Cheers,
>
> Carl Reynolds Ph: +64-9-4154790
> CJN Technologies Ltd. Fax: +64-9-4154791
> [EMAIL PROTECTED] DDI: +64-9-4154795
> PO Box 302-278, North Harbour, Auckland, New Zealand
> 12 Piermark Drive, North Harbour Estate, Auckland, NZ
> Visit our website at http://www.cjntech.co.nz/
application/ms-tnef
