Read Binary file using MsgPack in C++ - c++

Question

I want to read a binary file using Cpp, and its type is using MsgPack.
I'm not familiar with MsgPack and I try to read binary file fist and push in MsgPack. It doesn't work. It just gets the first number again and again. Can anyone help? Thanks a lot.
#include <bits/stdc++.h>
#include <msgpack.hpp>
using namespace std;
int main()
{
std::ifstream ifs("input.txt", std::ifstream::in);
std::stringstream buffer;
buffer << ifs.rdbuf();
msgpack::unpacked upd;
msgpack::unpack(upd, buffer.str().data(), buffer.str().size());
std::cout << upd.get() << std::endl;
return 0;
}
Which it can just get the first number "3".
I'm hoping to get number:
3
[3 6 7 5 3 5]
[6 2 9 1 2 7]
[0 9 3 6 0 6]
And here is the input binary file.

Answer 1

msgpack::unpack() unpacks the first MessagePack formatted data.
I think that 3 means the number of following arrays.
In this case offset is useful. See https://github.com/msgpack/msgpack-c/wiki/v2_0_cpp_unpacker#client-controls-a-buffer
Here is the code reading the first MessagePack data 3 as the counter. And then 3 times call msgpack::unpack() to unpack each array.
During that process, the variable offset is updated.
#include <iostream>
#include <fstream>
#include <msgpack.hpp>
int main()
{
std::ifstream ifs("input.txt");
std::string buffer((std::istreambuf_iterator<char>(ifs)),
std::istreambuf_iterator<char>());
msgpack::unpacked upd;
std::size_t offset = 0;
msgpack::unpack(upd, buffer.data(), buffer.size(), offset);
std::size_t count = upd.get().as<std::size_t>();
std::cout << count << std::endl;
for (std::size_t i = 0; i != count; ++i) {
msgpack::unpack(upd, buffer.data(), buffer.size(), offset);
std::cout << upd.get() << std::endl;
}
}
I believe that this is the approach based on your original code.

Answer 2

Your code unpacks only one msgpack message (first one, which is 3) but actually your file contains 4 messages. So you can use msgpack::unpacker class to unpack all messages one by one.
int main()
{
std::ifstream ifs("input.txt", std::ifstream::in);
std::string buffer((std::istreambuf_iterator<char>(ifs)),
std::istreambuf_iterator<char>());
msgpack::unpacker pac;
pac.reserve_buffer( buffer.size() );
std::copy( buffer.begin(), buffer.end(), pac.buffer() );
pac.buffer_consumed( buffer.size() );
msgpack::object_handle oh;
while ( pac.next(oh) ) {
msgpack::object msg = oh.get();
std::cout << msg << std::endl;
}
return 0;
}
P.S.
Read this and stop using #include <bits/stdc++.h>.

Answer 3

i think problem here : buffer.str().size() you can try
buffer.str().length()
or strlen(buffer.str().data().c_str());