Am 28.02.2012 09:41, schrieb Mattias Gaertner:
On Tue, 28 Feb 2012 09:23:34 +0100
Sven Barth<[email protected]> wrote:
Am 28.02.2012 05:04, schrieb Martin Schreiber:
Hi,
I read that we should use TBytes instead of AnsiString in order to
implement combined binary/character buffers with automatic memory
management. With AnsiString we used setlength() in order to allocate not
initialized memory.
TBytes is defined as
"
TBytes = array of Byte;
"
where setlength() fills the buffer with zeros. What should we use instead?
For strings SetLength also fills the string with zeros as the following
example shows:
=== example begin ===
program setlengthtest;
var
barr: array of Byte;
b: Byte;
s: AnsiString;
c: Char;
begin
SetLength(barr, 20);
for b in barr do
Write(b, ' ');
Writeln;
SetLength(s, 20);
for c in s do
Write(Ord(c), ' ');
Writeln;
end.
=== example end ===
=== output begin ===
PS P:\tests\oneshots> .\setlengthtest.exe
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
That's because the OS gives you on first time a lot of zeroed mem.
SetLength does not zero memory. Try this:
var
i: Integer;
s: string;
begin
for i:=1 to 100000 do begin
SetLength(s,1000000); // size does not matter for speed
SetLength(s,1);
end;
end.
In the end I preferred looking at the source of SetLength as written to
Martin already ;)
Regards,
Sven
_______________________________________________
fpc-devel maillist - [email protected]
http://lists.freepascal.org/mailman/listinfo/fpc-devel
