Deep Analysis of Const Qualifier in C

Question

Where does a const variable gets stored exactly and how does it behaviour change? Say for example:

const int i=10; // stores where ?  
main()  
         


        

Answer 1

Modifying your code to print the value:

#include 

main()
{
   const int j=20;
   int *p;
   p=&j;
   (*p)++;
    printf("%d\n", j);
   return 0 ;
}

The above code, when compiled with gcc 4.3.2 at -O1 optimisation or above, results in the output 20 rather than 21. This shows that it hasn't really "worked" - it just appeared to work.

A const qualifier isn't a request to have the variable placed in a particular kind of memory - it's a promise from you to the compiler, that you won't modify that variable by any means. The compiler can rely on your promise to optimise the code that's produced - and if you break your promise, it won't necessarily break in an obvious way, it may just produce strange results.