C++ how to convert any class (custom) object to vector

Question

I have defined my own class :

class Rectangle {
  int width;
  int height;
};

I want to convert any such class object to vector<unsigned char>. I tried doing it for particular types, and then for any type:

template< typename T > std::vector< byte, sizeof(T) >  to_bytes( const T& object ) {
    std::vector< byte, sizeof(T) > bytes ;
    const byte* begin = reinterpret_cast< const byte* >(std::addressof(object)) ;
    const byte* end = begin + sizeof(T) ;
    std::copy( begin, end, std::begin(bytes) ) ;
    return bytes ;
}

But this is valid only for a particular type in C++. How can I convert my Rectangle class, or any user defined class for that matter to vector<unsigned char> ?

`std::vector`'s second parameter is its allocator. I don't know what you're trying to do — Passer By, Nov 27 '17 at 07:53
It will create a vector of `sizeof(T)` bytes ? I am not sure. I am getting errors in compilation. Sorry I am new to C++ — user17836, Nov 27 '17 at 07:54
@user3636955, *absolutely no*. I recommend reading some documentation before trying to use it. — Incomputable, Nov 27 '17 at 07:54
I am referring here: http://www.cplusplus.com/forum/beginner/155821/ — user17836, Nov 27 '17 at 07:54
"It will create a vector of sizeof(T) bytes ?" No it will not. What makes you think so? I recommend getting a C++ book. — n. m. could be an AI, Nov 27 '17 at 07:55
Possible duplicate of [How do you serialize an object in C++?](https://stackoverflow.com/questions/523872/how-do-you-serialize-an-object-in-c) — Passer By, Nov 27 '17 at 07:55
@user3636955, it is written there explicitly, `std::array`. `std::array` and `std::vector` are different. — Incomputable, Nov 27 '17 at 07:56
1. The page you link doesn't mention std::vector at all. 2. cplusplus.com is not recommended as a beginner's resource, it's full of errors. — n. m. could be an AI, Nov 27 '17 at 07:57
Can you help me on how I can modify the code to obtain `std::vector` ? Instead of `std::array` — user17836, Nov 27 '17 at 08:02
@n.m. can you give me a reference to how I can convert any type to vector ? I am new to c++ and would like to understand that. — user17836, Nov 27 '17 at 08:32
I want to store it in a data structure that needs `std::vector`. I am using this trie : https://github.com/ethereum/cpp-ethereum/blob/develop/libdevcore/TrieDB.h , the `insert` function. But I would like to serialize any class to `std::vector` basically. — user17836, Nov 27 '17 at 08:38

score 1 · Answer 1 · answered Nov 27 '17 at 11:45

1

You could do this by making a user defined type conversion in Rectangle class:

explicit operator vector<unsigned char>() const {
// Do something here
}

Hope this helps.

answered Nov 27 '17 at 11:45

Jake Freeman

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C++ how to convert any class (custom) object to vector

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