忽略注释:打包位字段的偏移量而不使用“-Wno-packed-bitfield-compat”

时间:2016-12-21 01:22:28

标签: c++ c++11 gcc-warning gcc4.4

当我尝试编译以下联合时,我会弹出此警告: 10:5: note: offset of packed bit-field 'main()::pack_it_in::<anonymous struct>::two' has changed in GCC 4.4

#pragma GCC diagnostic ignore "-Wpacked-bitfield-compat"
union pack_it_in {
    struct
    {
        uint8_t zero : 3;
        uint8_t one : 2;
        uint8_t two : 6;
        uint8_t three : 4;
        uint8_t four : 1;
    } __attribute__((packed)) u8_2;
    uint16_t u16;
};
#pragma GCC diagnostic pop

#pragma不会忽略该注释。有没有办法让#pragma在不必使用-Wno-packed-bitfield-compat的情况下工作,因为我希望仅在我的八个工会中有两个忽略此警告?

2 个答案:

答案 0 :(得分:0)

就遇到了类似的问题。看来gcc只是不喜欢跨越类型宽度的位域(如示例中的two一样)?

如果将所有类型都更改为uint16_t,则gcc会接受:

union pack_it_in {
    struct
    {
        uint16_t zero  : 3;
        uint16_t one   : 2;
        uint16_t two   : 6;
        uint16_t three : 4;
        uint16_t four  : 1;
    } __attribute__((packed)) u8_2;
    uint16_t u16;
};

布局就是您想要的布局,即使这些成员的类型可能不是。

答案 1 :(得分:-1)

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpacked-bitfield-compat"
union pack_it_in {
    struct
    {
        uint8_t zero : 3;
        uint8_t one : 2;
        uint8_t two : 6;
        uint8_t three : 4;
        uint8_t four : 1;
    } __attribute__((packed)) u8_2;
    uint16_t u16;
};
#pragma GCC diagnostic pop