C指针/数组值混淆

Question

假设我们有以下代码:

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;
}

运行时结果如下:

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

可以看到 one.s 和 one.e 的地址是相等的 - 正如预期的那样 - 但值不同。这就是让我感到困惑的地方。

Answer 1

one.e是one.e数组的地址。 one.s 是 one.s 的值。如果你想要 e 的值，你需要访问 one.e[0]...one.e[3]。