man malloc

Giorgos Keramidas keramida at
Fri Aug 19 10:52:39 GMT 2005

On 2005-08-18 22:17, Dmitry Mityugov <dmitry.mityugov at> wrote:
>On 8/18/05, Giorgos Keramidas <keramida at> wrote:
>>On 2005-08-18 12:08, Sergey Matveychuk <sem at> wrote:
>>>Chuck Swiger wrote:
>>>>>What is pointer coercion? I have no pointer before malloc() returns.
>>>> Right.  Well, malloc returns a (void *), but most people want to use the
>>>> memory malloc returns to hold their own arrays, structs, whatever, which
>>>> means that you need to be able to coerce the (void *) malloc gave you
>>>> into whatever pointer type you want to actually use.
>>>> So the memory malloc gives you needs to be aligned so that it's OK to be
>>>> used for even the most restrictive datatype known to the system,
>>>> commonly 8, 16, or 32 bytes.
>>> Pointer coercion means a type cast? I see now.
>>> I read it as 'force change of pointer value' before.
>> It may be surprising, but casting back and forth *MAY* change the value
>> of the pointer.
> Could you back up this assertion with an example, please?

Do I really have to?

The standard says that casting is only allowed from (type *) to (void *)
and back to (type *).  This is exactly the reason why malloc() knows
(using its own "magic") what to return, so that you _can_ cast its

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