How to access global variable when there is a local and global conflict

Question

Code :

int a = 33;
int main()
{
  int a = 40; // local variables always win when there is a conflict between local and global.
  // Here how can i access global variable 'a' having value '33'.
}

If you ask : Why would someone want to do above thing? Why [a-zA-Z]* ?

My answer would be : Just to know that 'it is possible to do so'.

Thanks.

Solution 1

How about this old trick:

int main()
{
    int a = 40; // local variables always win when there is a conflict between local and global.

    {
        extern int a;
        printf("%d\n", a);
    }
}

Solution 2

int a = 33;
int main()
{
  int a = 40;
  int b;
  {
    extern int a;
    b = a;
  }
  /* now b contains the value of the global a */
}

A harder problem is getting a if it's static with file scope, but that's also solvable:

static int a = 33;
static int *get_a() { return &a; }
int main()
{
  int a = 40;
  int b = *get_a();
  /* now b contains the value of the global a */
}

Solution 3

IT IS C++, I OVERLOOKED C tag, SORRY !

int a = 100;

int main()
{
    int a = 20;

    int x = a; // Local, x is 20

    int y = ::a; // Global, y is 100

    return 0;
}

Comments

[R.. GitHub STOP HELPING ICE]

+1 for beating me by 30 seconds.

[Heisenbug]

+1: nice trick..didn't know about that.

[cnicutar]

@R.. To be fair, I think I first saw it some time ago in one of your older posts.

[Grijesh Chauhan]

@cnicutar when would you prefer to access via pointer compare to extern keyword ? I think it will work for global static variable too. correct ?

[cnicutar]

@GrijeshChauhan I think it's best to avoid name collisions in the first place, by defensively naming objects and functions your code exports (i.e. everything not static). On the other hand, if you already have a pointer there's no need for this trick.

[ad absurdum]

Why not just do int b = a; int a = 40;? Or, might the compiler reorder the lines in this case....

[R.. GitHub STOP HELPING ICE]

Indeed you could do that.

[void]

it didn't work, I'm using DigitalMars compirer