Correct ways to gather messages form different dbc files into common map

[baruchli]

I want to get messages from number of dbc files into common map.
The code looks like

1     std::string dbcsDir(argv[2]);
2     std::unique_ptr<dbcppp::INetwork> net;
3     for (const auto & entry : fs::directory_iterator(dbcsDir)){
4         std::ifstream idbc(entry.path());
5         // After this line msg(s) inserted from previous dbc file are cleared from memory
6         // and messages holds invalid pointers. 
7         net = dbcppp::INetwork::LoadDBCFromIs(idbc); 
8         for (const dbcppp::IMessage& msg : net->Messages())
9         {
10            messages.insert(std::make_pair(msg.Id(), &msg));
11        }
12    }

The problem with this code is the next:
msg entries added to messages map in line 10 became invalid in the next round of for loop after line 7.
Those entries still may be found at messages map, but call like

1     std::unordered_map<uint64_t, const dbcppp::IMessage*>::iterator iter; 
2     iter = messages.find(<first added id>);
3     if (iter_test != messages.end())
4         {
5             const dbcppp::IMessage* msg = iter_test->second;
6             std::cout << msg->Name() << std::endl;
7         } 

brings crash in line 7.

Whats is a correct ways to get messages form number of dbc files into single map?

[xR3b0rn]

The ownership of the dbcppp::IMessage object still lays in the hand of the dbcppp::INetwork-instance. So once the dbcppp::INetwork-instances destructor is called, your stored pointer in line 10 gets invalidated.

The correct way is to not let the dbcppp::INetwork-instances run out of scope by e.g. storing them in a std::vector:

std::string dbcsDir(argv[2]);
std::vector<std::unique_ptr<dbcppp::INetwork>> net;
for (const auto & entry : fs::directory_iterator(dbcsDir)){
      std::ifstream idbc(entry.path());
      // After this line msg(s) inserted from previous dbc file are cleared from memory
      // and messages holds invalid pointers. 
      net.emplace_back(dbcppp::INetwork::LoadDBCFromIs(idbc));
      for (const dbcppp::IMessage& msg : net->Messages())
      {
            messages.insert(std::make_pair(msg.Id(), &msg));
      }
 }

[baruchli]

Thank you, this solved the problem.

Naturally, line
for (const dbcppp::IMessage& msg : net->Messages())
must be changed to line
for (const dbcppp::IMessage& msg : net.back()->Messages())

[xR3b0rn]

It's propably interesting to note, that it's also possible to use the Merge-function of dbcppp::INetwork in order to merge two different dbcppp::INetworks into one:

std::string dbcsDir(argv[2]);
std::unique_ptr<dbcppp::INetwork> net;
for (const auto & entry : fs::directory_iterator(dbcsDir))
{
    std::ifstream idbc(entry.path());
    if (!net) net = dbcppp::INetwork::LoadDBCFromIs(idbc);
    else
    {
        auto tmp = dbcppp::INetwork::LoadDBCFromIs(idbc);
        net->Merge(tmp);
    }
}
// After this line msg(s) inserted from previous dbc file are cleared from memory
// and messages holds invalid pointers. 
for (const dbcppp::IMessage& msg : net->Messages())
    messages.insert(std::make_pair(msg.Id(), &msg));

[baruchli]

This power ability, but not relevant in my case.
I will consider it for future use.