• RADHA GOGIA (22/22) Sep 19 2015 I went through these two links and found that this behaviour is
• Adam D. Ruppe (7/18) Sep 19 2015 const in C (and D) isn't necessarily related to read-only memory

RADHA GOGIA <radhagogia8 gmail.com> writes:

I went through these two links and found that this behaviour is 
undefined , but the only issue which I have is that in one sense 
we say that since local variables live on stack , hence they 
cannot be located on read only memory region but if this is so 
then if I try to alter the value of the constant directly through 
assignment then why does it show error if it is not located in 
the read only memory region :

#include<stdio.h>
int main()
{
const int a=12;
int *ptr ;
ptr=&a;
*ptr=8; // no error
a=45; // error
printf("\n %d", a);
return 0;
}


1. 
http://stackoverflow.com/questions/945640/why-can-i-change-a-local-const-variable-through-pointer-casts-but-not-a-global-o


2. 
http://stackoverflow.com/questions/3801557/can-we-change-the-value-of-a-constant-through-pointers

Adam D. Ruppe <destructionator gmail.com> writes:

On Sunday, 20 September 2015 at 00:09:52 UTC, RADHA GOGIA wrote:
 I went through these two links and found that this behaviour is 
 undefined , but the only issue which I have is that in one 
 sense we say that since local variables live on stack , hence 
 they cannot be located on read only memory region but if this 
 is so then if I try to alter the value of the constant directly 
 through assignment then why does it show error if it is not 
 located in the read only memory region :


const in C (and D) isn't necessarily related to read-only memory 
on the hardware level. It is a feature of the type system - 
because the VARIABLE is marked const, the compiler will complain 
if you try to write to it.


 const int a=12;
 int *ptr ;
 ptr=&a;
 *ptr=8; // no error

BTW, that is allowed in C, but would be a compile error in D - 
D's type system propagates the const to pointers too.