将结构作为二进制数据插入向量中以进行网络传输

Question

I am using an older network transmission function for a legacy product, which takes a char array and transmits it over the network. This char array is just data, no need for it make sense (or be null terminated). As such in the past the following occurred:

struct robot_info {
    int robot_number;
    int robot_type;
    ...
} // A robot info data structure for sending info.


char str[1024], *currentStrPos = str;
robot_info r_info; 
... // str has some header data added to it.
... // robot info structure is filled out
memcpy(currentStrPos, (char *)&r_info, sizeof robot_info); // Add the robot info
scanSocket.writeTo(str, currentStrPos - str); // Write to the socket.

We have just added a bunch of stuff to robot_info but i am not happy with the single length method of the above code, i would prefer a dynamiclly allocated raii type in order to be expandable, especially since there can be multiple robot_info structures. I propose the following:

std::vector<char> str;
... // str has some header information added to it.
... // r_info is filled out.
str.insert(str.end(), (char *)&r_info, (char *)&r_info + sizeof r_info); 
scanSocket.writeTo(str.data(), str.size());

Live example.

Using the std::vector insert function (with a pointer to the start of r_info as the iterator) and relying on the fact that a struct here would be aligned to at least a char and can be operated on like this. The struct has no dynamic memory elements, and no inheritance.

Will this have well defined behavior? Is there a better way to perform the same action?

Answer 1

While this works, it is ultimately solving a compile time problem with a run time solution. Since robot_info is a defined type, a better solution would be this:

std::array<char, sizeof robot_info> str;
memcpy(str.data(), static_cast<char *>(&r_info), sizeof robot_info);
scanSocket.writeTo(str.data(), str.size());

This has the advantages:

1. Can never be over size, or undersized
2. Automatic Storage duration and stack allocation means this is potentially faster