Jonas Maebe пишет:
On 01 Mar 2011, at 07:32, Paul Ishenin wrote:
I noticed today that if I want to allocate 0 bytes I get not a nil but
a valid pointer. Why?
The current code that causes this comes from this (cvs) revision:
revision 1.16
date: 1999-09-17 19:14:12 +0200; author: peter; state: Exp; lines:
+284 -966;
+ new heap manager supporting delphi freemem(pointer)
I guess the reason was to be able to
a) give a run time error if someone tries to do freemem(nil)
Delphi allows freemem(nil) without error, consistent with TObject.Free
b) nevertheless allow freeing all pointers that have been allocated
using getmem() (even if the size was 0 bytes), for backwards
compatibility with FPC code from before that revision (FPC also returned
a non-nil pointer in that case)
This is incompatible with delphi.
I remember a discussion some time ago, the conclusion was it's compatible with
TP
rather than with Delphi.
If it is changed, it will also require changes in cmem (and probably
also in heaptrc), because at least on Mac OS X libc also returns a valid
pointer for malloc(0).
Not necessary, if we have only one GetMem function (currently we have several - getmem, fpc_getmem,
getmemory and maybe something else, each calling MemoryManager independently) and write it like this:
if size=0 then
result := nil
else
result := MemoryManager.GetMem(size);
And I suppose cause crashes and memory leaks not only in my delphi
code which I'm porting to FPC/Lazarus.
That sounds very much like badly written code.
Fully agree.
Sergei
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