C related question

Hello why i can not change a global const variable with a local pointer variable. while if const is local i can change it by a local pointer.

const
 int val1=10;
 int main()
  {
    int *ptr;
    ptr=&val1;
   *ptr=5;
    printf("%d\n",*ptr);
 }
 

it doesn't work while

int main()
 {
   const int val1=5;
    int *ptr;
    ptr=&val1;
   *ptr=10;
    printf("%d\n",*ptr);
 }

works fine what is the reason behind?

Global constants goes in RO section of the binary hence you cannot change them. whereas when you define a local variable with const attribute and then try to change in your program, you will be able to do it as the memory assigned to local variable is on stack. however if you try to define your local constant as static it goes to the RO section and you will get the same result as that of global constant. i.e. you wont be able to change it.

In terms of C language, this considered as an error as you are trying to assign a constant to a pointer of variable type. C compiler usually throws a warning "warning" to avoid breaking of code.

Hi Sir,Thanks for your reply i am asking about first one again what if i declare a pointer globally. can i modify it by global pointer?

No you cannot. As I said, global constants are stored in RO (read only) section which cannot be modified.

The only reason to declare a variable const (constant) is to tell the compiler not to
allow it to be changed.
If you want to change a variable using pointers of any kind, don't declare it const