Date: Wed, 11 Jul 2007 00:57:52 +0200 From: Erik Trulsson <ertr1013@student.uu.se> To: Andrey Chernov <ache@nagual.pp.ru>, Peter Jeremy <peterjeremy@optushome.com.au>, freebsd-current@freebsd.org Subject: Re: HEADS UP: getenv() and family API change Message-ID: <20070710225752.GA3000@owl.midgard.homeip.net> In-Reply-To: <20070710224619.GA31654@nagual.pp.ru> References: <20070703182400.Q1449@baba.farley.org> <Xuu8UV3Bay@dmeyer.dinoex.sub.org> <20070709145418.T52164@thor.farley.org> <20070710154148.GA22873@nagual.pp.ru> <20070710213602.GX3434@turion.vk2pj.dyndns.org> <20070710224619.GA31654@nagual.pp.ru>
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On Wed, Jul 11, 2007 at 02:46:19AM +0400, Andrey Chernov wrote: > On Wed, Jul 11, 2007 at 07:36:02AM +1000, Peter Jeremy wrote: > > On 2007-Jul-10 19:41:48 +0400, Andrey Chernov <ache@nagual.pp.ru> wrote: > > >To say strictly, copying somewhere is not neccessary since this way works > > >too: > > > > > >static char *s = "PATH=/bin"; > > > > > >putenv(s); > > > > I thought the C compiler was still free to place the string into RO > > memory and/or coalesce it with other strings in that case. > > > > Wouldn't the following be clearer (s is forced to be writable): > > > > static char s[] = "PATH=/bin"; > > > > putenv(s); > > This two are the same, since there is no "const", so compiler can't put > static char *s > into RO memory. Not the pointer, but the string it points to can be put into read-only memory. Example: static char *s = "PATH=/bin"; static char *t = "PATH=/bin"; Here both 's', and 't' can point into read-only memory where the string "PATH=/bin" has been placed. Not only that, they may point to the same place, i.e. there need only be one copy of the string "PATH=/bin" in the program (but there may be two distinct copies if the compiler does not coalesce identical string constants.) If on the other hand you use static char s[] = "PATH=/bin"; static char t[] = "PATH=/bin"; Then 's' and 't' are no longer pointers to a string constant, but arrays that are initialized with the string "PATH=/bin". These arrays are modifiable and distinct - i.e. there will be (at least) two copies of the string "PATH=/bin" in memory. -- <Insert your favourite quote here.> Erik Trulsson ertr1013@student.uu.se
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