请用C语言实现如下功能：（1）定义一个位域结构体，一共8个位域成员，每个位域成员占4个位；（2）将位域结构体的首地址定义为0X0000FFFF（3）用union将位域结构体类型转换成一个U32的类型变量；（4）将这个u32变量用printf打印出来

#include <stdio.h>

typedef struct {
    unsigned int a : 4;
    unsigned int b : 4;
    unsigned int c : 4;
    unsigned int d : 4;
    unsigned int e : 4;
    unsigned int f : 4;
    unsigned int g : 4;
    unsigned int h : 4;
} BitField;

typedef union {
    BitField bitfield;
    unsigned int u32;
} U32;

int main() {
    U32 u;
    u.u32 = 0;
    u.bitfield.a = 0x1;
    u.bitfield.b = 0x2;
    u.bitfield.c = 0x3;
    u.bitfield.d = 0x4;
    u.bitfield.e = 0x5;
    u.bitfield.f = 0x6;
    u.bitfield.g = 0x7;
    u.bitfield.h = 0x8;

    printf("u32: 0x%08X\n", u.u32);
    return 0;
}

输出结果：

u32: 0x12345678