[fpc-devel] TBytes

[Sven Barth]

Am 28.02.2012 08:40, schrieb Martin Schreiber:
> Am 28.02.2012 09:23, schrieb Sven Barth:
>>
>> 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
>>
>> === output end ===
>>
>> So SetLength is the operation to use in each case.
>>
> This is probably because in your testcase the memory is still clean, try
> with -gh. Additionally this behavior would not be Delphi compatible:
> "
> When you use SetLength, existing characters in the string are preserved,
> but the contents of any newly allocated space is undefined.
> "
> http://docwiki.embarcadero.com/RADStudio/en/Declaring_and_Initializing_Strings

You are right, I checked the code of SetLength for arrays and strings 
and only arrays use FillChar. Nevertheless there is no other operation 
you can use for arrays.

Regards,
Sven