Re: [Dev-C++] Why thisC example don't presents the correct result ?

[Paul I. <pi...@ot...>]

Quoting hu...@cl...:
=09
> 		Hi all,=20
> 		in others compilers this is the result :=20
> 	=09
> 		10=20
> 		200=20
> 	=09
> 		of this program :=20
> 		#include=20
> 		main <http://pcp.clix.pt/images/canais/webmail2/smile/kiss.gif>=20
> 		{=20
> 		int v[3],i;=20
> 		v[0]=3D10;=20
> 		v[1]=3D200;=20
> 		i=3D0;=20
> 		while(v[i]!=3D'\0')=20
> 		{=20
> 		printf("%d\n",v[i]);=20
> 		i++;=20
> 		}=20
> 		}=20
> 	=09
> 		in dev-c++compiler i have the this result :=20
> 		10=20
> 		200=20
> 		2293664=20
> 		4198592=20
> 		4210688=20
> 		4210692=20
> 		2293664=20
> 		4198757=20
> 		1=20
> 		4138088=20
> 		4139640=20
> 		4198553=20
> 	=09
> 	=09
> 		Why ?????=20
> 	=09
> 		Thanks.=20
>=20
> 		--
> 		Hugo Dias
> 		 =20


Well, to me it seems that the explanation is that GCC stores the variable=
s
declared in main on the stack! If you put the declaration of the v vector
outside main, the program will "work" just as with the other compilers. T=
his
probably is because windoze will clear the memory (setting to zero) alloc=
ated to
the program before loading and executing it. The memory occupied by the s=
tack is
cleared just like all the rest, only it is messed up by some initializati=
on code
executed before main starts executing.

If you put the same code in some other function than main it won't work (=
except
by chance) regardless of which compiler you use.


A way to verify this behavior is to put "int v[3000000]" outside of main =
and
inside. And yes, the program crashes if you put the declaration inside ma=
in,
because windows don't allow you to allocate that much (at once) on the st=
ack. My
guess is that the other compilers treat declarations inside main as if th=
ey were
put outside of main (go ahead and try).=20

Note that the clearing of memory before loading and executing the program=
 is not
 part of the C/C++ standards but is dependent on the OS. Visal C++ (when
debugging) even initialize memory to 0xaa (or was it 0x55?) to help detec=
ting
this kind of bugs.=20

/Paul I