<分区>
我有以下代码:
#include <iostream>
#include <bitset>
#pragma pack(1)
typedef uint8_t flag_t;
typedef struct flag_struct_t {
flag_t f1:1;
flag_t f2:2;
flag_t f3:2;
flag_t f4:2;
flag_t f5:1;
} flag_struct_t;
int main() {
const uint8_t flagValue = 96;
std::bitset<8> mybits(flagValue);
const flag_struct_t flag = *reinterpret_cast<const flag_struct_t*>(&flagValue);
std::cout << "f2 = " << (uint16_t)flag.f2 << std::endl;
std::cout << "f3 = " << (uint16_t)flag.f3 << std::endl;
std::cout << "f4 = " << (uint16_t)flag.f4 << std::endl;
std::cout << "bitset = " << mybits << std::endl;
std::cout << "size of flag_struct_t = " << sizeof(flag_struct_t) << std::endl;
}
#pragma pack()
输出是:
$ ./mybitset
f2 = 0
f3 = 0
f4 = 3
bitset = 01100000
size of flag_struct_t = 1
似乎结构成员的顺序已从 f1, f2, f3, f4 反转为 f4, f3, f2, f1。
这是为什么？
如果重要的话，我正在使用 GCC 8。
谢谢!