如何将 map 阵列塞入缓冲区以发送？

Question

I am trying to move the map array but for this I need to put everything in buffer, here is my code.

#include <iostream>
#include <map>
#include <string>

    std::map<std::int, std::string> maphack;
    maphack.emplace(1, "CS");
    maphack.emplace(2, "PBG");
    maphack.emplace(3, "Maicraft");
    maphack.insert_or_assign(3, "GTA5");

    for (auto &a : maphack) {
        std::cout << a.first << " : " << a.second << '\n';
    }

How to put everything above in the buffer?

char buffer[64];

send(sock, buffer, AmountToSend, 0);

Answer 1

The simple answer is to use std::ostringstream and std::istringstream which allows to use std streams machinery with a string storage. Which can be converted to char* with c_str() method if needed later, full example is below.

The better answer can be to use more heavy lifting library for serialization, the choice of the format will depend on your program. Do you need binary or text format? Do you want other programs (in other programming languages) be able to read it? Do you need to support different endian system? Do you need to handle error when deserializing malformed input? Boost, Qt, google protobuf, and other ones are out there.

#include <iostream>
#include <map>
#include <sstream>
#include <string>

void write_map(const std::map<int, std::string> &m, std::ostream &out) {
  for (auto &a : m) {
    out << a.first << " " << a.second << '\n';
  }
}

std::map<int, std::string> read_map(std::istream &in) {
  std::map<int, std::string> m;
  int i;
  std::string s;
  while (in >> i >> s) {
    m.emplace(i, s);
  }
  return m;
}

int main() {
  std::map<int, std::string> m;
  m.emplace(1, "CS");
  m.emplace(2, "");
  m.emplace(3, "Maicraft");
  m.insert_or_assign(3, "GTA5");

  std::ostringstream out;
  write_map(m, out);
  std::string data = out.str();
  std::cout << "Data:\n" << data << std::endl;

  // send data over socket
  // ...

  std::istringstream in(data);
  auto m1 = read_map(in);
  std::cout << "Read:\n";
  write_map(m1, std::cout);
  std::cout << std::endl;
}