通過C ++套接字（linux）發送std :: map <int，std :: map <std :: string，double >>

Question

我試圖在linux中通過TCP套接字發送由int和另一個映射組成的映射。

地圖是形式

map<int, map<string, double>>

按照這個SO鏈接我試着做

unsigned char* mybytemap =  reinterpret_cast<unsigned char*>(&my_map);

然后發送緩沖區我用write（）函數如下：

int size = sizeof(mybytemap);
char temp[10];
sprintf(temp, "%d", size);
write(sockfd, temp, strlen(temp));     //send the size for the client
write(sockfd, mybytemap, sizeof(mybytemap));

在客戶端：

char temp[10];
n  = read(sockfd, temp, 10);
size = stoi(temp);    //Got Size Of buffer

unsigned char * buf;
if(size != 0)
{
    buf = new unsigned char[size];
    int current=0;
    while(current<size)
    {
        n = read(sockfd,(unsigned char*)(buf)+current, min(1024,size-current));
        if (n <= 0)
        {
            cout<<"ERROR reading from socket when receiving"<<endl;
            break;
        }
        current+=n;
    }
}

map<int, map<string, double>> *test = reinterpret_cast< map<int, map<string, double>>* > (buf);

vector<int> ks;
for(map<int, map<string, double>>::iterator it = test->begin(); it != test->end(); ++it)
{
    ks.push_back(it->first);
    cout<<"id: "<<it->first<<endl;
}

但是在嘗試訪問數據時未正確接收Map並且代碼崩潰。 怎么解決這個問題？

我需要XML地圖嗎？ 若有，有人可以指導我如何做到這一點？

Answer 1

您的問題中的鏈接答案不適用於地圖（地圖不是pod）

一般的想法如何編碼\\ decode map：編碼map的大小然后為每個鍵/值編碼密鑰的大小，然后編碼密鑰，然后編碼值的大小，然后編碼值。 以下代碼假定您將size_t編碼為sizeof（size_t）字節

template<class T>
std::string encode(T value){
   // data to bytes
}

template<class T> 
T decode(std::string bytes){
  // bytes to data
}

template<class K, class V>
std::string encode_map(std::map<K, V> data){
  std::string result;
  result.append(encode<size_t>(data.size()));
  for(auto iter: data){
    std::string first = encode<K>(iter.first);
    result.append(encode<size_t>( first.size() ));
    result.append(first);
    std::string second = encode<V>(iter.second);
    result.append(encode<size_t>( second.size() ));
    result.append(encode<V>(iter.second));
  }
  return result;
}

template<class K, class V>
std::map<K, V> decode_map(std::string bytes){
  size_t index = 0;
  size_t size = decode<size_t>(std::string(bytes.begin()+index, bytes.begin()+index+sizeof(size_t) ) );
  index += sizeof(size_t);
  std::map<K, V> result;
  for(size_t i = 0; i<size; i++){
    size_t next_size = decode<size_t>(std::string(bytes.begin()+index, bytes.begin()+index+sizeof(size_t) ) );
    index += sizeof(size_t);
    K key = decode<K>(std::string(bytes.begin()+index, bytes.begin()+index+next_size ) );
    index += next_size;
    next_size = decode<size_t>(std::string(bytes.begin()+index, bytes.begin()+index+sizeof(size_t) ) );
    index += sizeof(size_t);
    V value = decode<V>(std::string(bytes.begin()+index, bytes.begin()+index+next_size ) );
    index += next_size;
    result[key] = value;
  }
  return result;
}

Answer 2

按照建議，您需要執行所謂的序列化 。 您可以將Boost.Serialization用作序列化庫。 它可以處理所有STL類型。 一個說明性示例：

std::map<int, std::map<std::string, double>> m1;
// ... (fill m1)

// serialize into a buffer (string):
std::string buffer;
boost::iostreams::back_insert_device<std::string> inserter(buffer);
boost::iostreams::stream<boost::iostreams::back_insert_device<std::string>> ostr(inserter);
boost::archive::binary_oarchive oa(ostr);
oa << m1;
ostr.flush();

// ... (here you can send the contents of buffer as plain bytes-chars via socket)

// deserialize into new map:
boost::iostreams::basic_array_source<char> device(buffer.data(), buffer.size());
boost::iostreams::stream<boost::iostreams::basic_array_source<char>> istr(device);
boost::archive::binary_iarchive ia(istr);
std::map<int, std::map<std::string, double>> m2;
ia >> m2;

完整的現場演示（包括所有標題）： https ： //wandbox.org/permlink/NyZeVTrFI0p8RcmY