将打包结构成员的引用传递给模板.gcc 错误?-C/C++问题

Passing reference of packed struct member to template. gcc bug?(将打包结构成员的引用传递给模板.gcc 错误?)

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问题描述

我遇到了一个问题，将结构成员传递给模板函数.该函数的目标是获取成员的地址和大小.这是一个简单的例子:

I encountered a problem, passing struct member to a template function. The function's goal is to take the address and size of the member. Here is simple example:

这是结构.它具有打包属性.

This is the struct. It has packed attribute.

struct TestStruct {
    unsigned char       elem1;
    unsigned char       elem2;
    uint64_t            elem3;
    char                buf[10000];
    int                 elem4;
    unsigned char       elem5;
}
__attribute__ ((packed));

这是模板函数，它应该得到一个成员的地址

this is the template function, which should get a member's address

template<typename T>
void addData(const T &val)
{
        printf ("address inside func: %p 
",&val);
}

int main(int argc, char *argv[])
{
        TestStruct testdata;
        testdata.elem4 = 0;
        printf ("struct address is:   %p 
",&testdata);
        printf ("elem4  address is:   %p 
",&testdata.elem4);
        addData(testdata.elem4);
        return 0;
}

问题:当属性((packed));已设置(如示例中所示)模板函数收到错误的成员地址:

The problem: When attribute ((packed)); is set (like in the example) the template function receives wrong address of the member:

输出:

struct address is:   0x7fff735bb4e0 
elem4  address is:   0x7fff735bdbfa 
address inside func: 0x7fff735bb4dc

如果我删除packed"属性，则一切正常.没有错误也没有警告(即使使用 -Wall -Wextra)，但没有将正确的地址传递给函数.

If I remove the "packed" attribute, everything is OK. There is no error and no warning (even with -Wall -Wextra), but not the right address is passed to the function.

我读了这个:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36566

发现有一个问题，获取对packed-struct成员的引用.很有趣，替换 const T&与 T&在我的模板函数中，产生错误消息:

and found that there is an issue, getting references to packed-struct members. Interesting enough, replacing const T& with T& in my template function, produces the error message:

error: cannot bind packed field ‘testdata.TestStruct::elem4’ to ‘int&’

所以，我有两个问题:

当其地址可以作为指针传递时，为什么不能将压缩结构成员作为常量引用传递

Why cannot packed-struct members be passed as const references, when their address can be passed as pointer

const T& 中发生了什么案件?没有错误，没有警告，但错误的地址被传递给函数.众所周知，引用的地址就是引用指向的变量的地址.

What happens in the const T& case? There is no error, no warning, but the incorrect address is passed to the function. As we know, the address of reference is the address of the variable, the reference points to.

将打包结构成员的引用传递给模板.gcc 错误?

问题描述

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