[fpc-devel] ReallocMem with CMem
daniel.mantione at freepascal.org
Wed Mar 8 18:31:02 CET 2006
Op Wed, 8 Mar 2006, schreef Micha Nelissen:
> On Wed, 8 Mar 2006 18:10:38 +0100 (CET)
> Daniël Mantione <daniel.mantione at freepascal.org> wrote:
> > Op Wed, 8 Mar 2006, schreef Micha Nelissen:
> > > Shouldn't ReallocMem in CMem zero the newly allocated bytes ?
> > No, it is the responsibility of the programmer.
> Nope. At least the compiler depends on it being zeroed. The FPC heap
> manager zeroes it, as well.
That is behaviour contrary to the documentation.
ReAllocMem resizes the memory pointed to by P so it has size Size. The
value of P may change during this operation. The contents of the memory
pointed to by P (if any) will be copied to the
new location, but may be truncated if the newly
allocated memory block is smaller in size. If a larger block is
allocated, only the used memory is initialized, extra
memory will not be zeroed out.
Note that P may be nil, in that case the behaviour of ReAllocMem is
equivalent to Getmem.
The ReallocMem procedure changes the storage size of
an existing block of storage.
The size may be smaller or bigger.
If smaller, then the existing storage is effectively
truncated, the remainder being released.
If larger, the storage is extended. Or a new block
is allocated if necessary. In either case, the
It is better to use New for this
existing storage block data is preserved, and the
new part is unitialised.
There is a good reason that the memory should not be initialised; you can
allocate large amounts of memory in advance. This memory is not actually
allocated by the OS until you use it. As soon as you initialize the
memory, it gets allocated immediately.
If the FPC heap manager initialises the memory, that functionality should
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