Most people here will be familiar with:

    #pragma pack(1)

    struct J {
       int a;
       char b;
       int c;
       char d;
       int e;
    };

    #pragma pack()

On most computers, this brings sizeof(J) down from 20 bytes to 14 bytes.

I have an idea about how to standardise this. Firstly we need a new
template class, "std::unaligned", which you can see defined here:

    https://github.com/healytpk/gcc-thomas-healy/blob/typedefangles/libstdc%2B%2B-v3/include/std/unaligned

So the aforementioned struct could then be written as:

    struct J {
       unaligned<int > a;
       unaligned<char> b;
       unaligned<int > c;
       unaligned<char> d;
       unaligned<int > e;
    };

But the above is a little tedious to write. That's why I suggest a new
form of 'typedef' that's followed by angle brackets, and you can use
it as follows:

    struct J {
      int a;
      char b;
      int c;
      char d;
      int e;
    };

    typedef< std::unaligned > J K;

As you guessed, the struct K will be the struct J but with every
member variable type enclosed in unaligned<>.

You can put any class template you want in there, for example:

    typedef< std::optional > J K;

Try out here up on GodBolt:

    https://godbolt.org/z/a8zoYavYE

Personally I think this is the No. 1 best strategy proposed so far to
add packed structs to standard C++.