C语言，判断机器大小端

union uc{unsigned long aa;char b[4];}test;int main(){test.aa = 0x12345678;printf("addr is %d char b[0] is %x\n",&test.b[0],test.b[0]);printf("addr is %d char b[1] is %x\n",&test.b[1],test.b[1]);printf("addr is %d char b[2] is %x\n",&test.b[2],test.b[2]);printf("addr is %d char b[3] is %x\n",&test.b[3],test.b[3]);}