Question

Say we have the following code:

typedef union {
   float    e[4];
   __v4sf   v;
   float    *s;
} __vec4f;

float test[12];


int main(){ 
__vec4f one;

printf("adrs: &one.s = 0x%x, &one.e = 0x%x\n", &one.s, &one.e);
printf("vals: one.s = 0x%x, one.e = 0x%x\n",one.s,one.e);
one.s = test;
printf("adrs: &one.s = 0x%x, &one.e = 0x%x\n", &one.s, &one.e);
printf("vals: one.s = 0x%x, one.e = 0x%x\n",one.s,one.e);

return 0;
}

When running the results are like follows:

adrs: &one.s = 0xbffff270, &one.e = 0xbffff270
vals: one.s = 0x927ff590, one.e = 0xbffff270
adrs: &one.s = 0xbffff270, &one.e = 0xbffff270
vals: one.s = 0x52a0, one.e = 0xbffff270

One sees that the address of one.s and one.e are equal – as expected – but the values aren’t.
This is what confuses me.

Answer 1

one.e is the address of the one.e array. one.s is the value of one.s. If you want the value of e you need to access one.e[0]…one.e[3].