c++ - 在 GCC 中为类使用属性打包

Question

海湾合作委员会文件 says :

You may only specify the packed attribute attribute on the definitionof an enum, struct or union, not on a typedef that does not alsodefine the enumerated type, structure or union.

这是否意味着我不能将此属性应用于类？

Answer 1

我在 GCC 文档中找不到清楚的答案，但通过以下实验，似乎可以。

#include <iostream>


struct UnPackedStruct {
    unsigned char a;
    int b;
};

struct __attribute__ ((__packed__)) PackedStruct {
    unsigned char a;
    int b;
};

class __attribute__ ((__packed__)) PackedClass{
    unsigned char a;
    int b;
};

int main()
{
    std::cerr << "sizeof( UnPackedStruct ): " << sizeof(UnPackedStruct)
            << ", sizeof( PackedStruct ): " << sizeof(PackedStruct)
            << ", sizeof( PackedClass): " << sizeof(PackedClass)
            << "\n";

    return 0;
}

输出:

sizeof( UnPackedStruct ): 8, sizeof( PackedStruct ): 5, sizeof( PackedClass): 5

Try it with online compiler