Question

Is it possible to get the value of unused variable using GDB? Is there some configuration for GCC so that the garbage value of the unused variable will be shown not ‘optimized out’?

c file:

#include<stdio.h>

void main()
{
    int x;
    int y;
    printf("value of x: %d",x);

}

In the gdb I want to get the garbage value of variable y.

(gdb) run
Starting program: /home/charmae/workspace/AVT/a.out 

Breakpoint 1, main () at file4.c:7
7       printf("value of x: %d",x);
(gdb) info locals
x = 2789364
(gdb) p y
$1 = <optimized out>
(gdb) p x
$2 = 2789364

Answer 1

It has nothing to do with GDB. The entity that optimized that variable out is the compiler (probably GCC in your case). You might force it to keep it by declaring the variable as volatile

A better question is – why are you trying to do?