Consider the following C program

#include <stdio.h>

typedef struct s {
  int x;
} s_t;

int main() {
  int x;
  s_t a;

  scanf("%d", &x);

  if (x > 0) {
    s_t a;
    a.x = x;
  }

  printf("%d\n", a.x);
}

The a struct variable in the if branch clearly shadows the a struct variable in main. One would expect that the output in printf would be undefined, but with GCC the scoped variable seems to equal the main variable.

For example

gcc test.c -o test
echo 10 | ./test

will output 10.

On the other hand, running this through clang, does as expected

clang test.c -o test
echo 10 | ./test

outputs -2145248048.

Is this a GCC bug or is there some sort of undefined behaviour that this is triggering?

gcc 4.8.2 clang 3.4