Date: Fri, 19 Aug 2005 00:40:03 +0300 From: Giorgos Keramidas <keramida@ceid.upatras.gr> To: Dmitry Mityugov <dmitry.mityugov@gmail.com> Cc: questions@freebsd.org Subject: Re: man malloc Message-ID: <20050818214003.GA687@flame.pc> In-Reply-To: <b7052e1e05081811172b36182e@mail.gmail.com> References: <4303A632.1000809@FreeBSD.org> <4303B016.3030201@mac.com> <43044212.20909@FreeBSD.org> <20050818125348.GG1282@flame.pc> <b7052e1e05081811172b36182e@mail.gmail.com>
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On 2005-08-18 22:17, Dmitry Mityugov <dmitry.mityugov@gmail.com> wrote: >On 8/18/05, Giorgos Keramidas <keramida@ceid.upatras.gr> wrote: >>On 2005-08-18 12:08, Sergey Matveychuk <sem@freebsd.org> 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 result.
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