test availability of variables in context from user command

[Christophe Demarey <Christophe.Demarey@inria.fr>]

Hello,

I want to check the availability of a variable (var1 for instance) in 
the context from an user command but I don't find any way to do this.
Here is a (dummy) example of what I want to do :

void func1(void)
{
    int var2 = 2;
    ...
}

int main(int argc, char **argv)
{
  int var1 = 1;
 
  ...
  func1();
}

My gdb command:
define myfunc
  if defined(var1)
     $res = $var1
  else
     $res = $var2
  end
  ...
end

If I break into main, res should be equals to 1, else res should be 
equals to 2.

Is there a way to do this with gdb?

Thanks,
Christophe.