Re: [PATCH] use ptrdiff_t instead of casting int magicks

On 09/06/2010 01:15 AM, Amos Jeffries wrote:
> Inspired from the SuSE patch submitted by Christian. This is what I
> think should be happening with real ptr maths instead of obsolete
> integer math with potential rounding and endian errors.

> void
> memNodeWriteComplete(void* d)
> {
> mem_node* n = (mem_node*)(d - _mem_node_data_offset);

GCC: pointer of type void * used in arithmetic

The value of a (pointer + n) expression depends on what pointer is
pointing to. If you want byte-size increments, you have to cast to char*
or similar.

Using ptrdiff_t instead of int is the right thing to do. I do not thing
you need to cast to it in makeMemNodeDataOffset. You may clarify the
intent by writing:

// calculate data member offset; p is not dereferenced here
mem_node *p = 0;
return reinterpret_cast<char*>(&p->data) - reinterpret_cast<char*>(p);

HTH,

Alex.
Received on Mon Sep 06 2010 - 15:41:33 MDT