How to iterate over a vector of many stucts

[871020905@qq.com]

I have many nodes, done data is stored in a struct like this:

  struct BriteNodeInfo
  {
    int nodeId;
    double xCoordinate;
    double yCoordinate;
    int inDegree;
    int outDegree;
    int asId;
    std::string type;
  };

Each node instance is stored in a vector like this:

  typedef std::vector<BriteNodeInfo> BriteNodeInfoList;

  BriteNodeInfoList m_briteNodeInfoList;

Problem: How do I wrire a function that write in a .txt file my node data like this:

nodeId0 yCoordinate0 xCoordinate0
nodeId1 yCoordinate1 xCoordinate1
nodeId2 yCoordinate2 xCoordinate2
nodeId3 yCoordinate3 xCoordinate3
etc...

I have tried but my iteration syntax is not good enough. Here is my function, please help:

void SaveNodeData (std::string fname)
{
  ofstream os(fname.c_str(), ios::trunc);

  vector<BriteNodeInfo> BriteNodeInfoList;
  BriteNodeInfoList m_briteNodeInfoList;

  for (BriteNodeInfoList::Iterator i = m_briteNodeInfoList.Begin(); i != m_briteNodeInfoList.End(); ++i)
    {  
        os << BriteNodeInfo[i].nodeId "\t" << "\t" << BriteNodeInfo[i].yCoordinate << "\t"BriteNodeInfo[i].xCoordinate<< "\n";
    }

    os << "\n";
 }

[2kaud]

What version of c++ are you using (c++98, c++11 or later)??

Can you use range-based for loops?

Consider for c++11 (not tried)

void SaveNodeData(const std::string& fname, const BriteNodeInfoList& bnil)
{
    ofstream os(fname, ios::trunc);

    if (!os.is_open()) {
        cout << "Cannot open file " << fname << endl;
        return;
    }

    for (const auto& bv : bnil)
        os << bv.nodeId << '\t' << bv.yCoordinate << '\t' << bv.xCoordinate << endl;

    os.close();
}

You need to pass the vector that contains the data you want to extract and store.

[wolle]

I have tried but my iteration syntax is not good enough.

You don't have to use iterators to iterate over a vector. You could also do it the old-fashioned way like,

  for (int i=0; i < int(m_briteNodeInfoList.size()); ++i)
    {  
        os << BriteNodeInfo[i].nodeId << "\t" << BriteNodeInfo[i].yCoordinate; << "\t" << BriteNodeInfo[i].xCoordinate << "\n";
    }

The size() function returns the number of elements in the vector. (it returns an unsigned int so it's cast to int to avoid a compiler warning.)

I'm mentioning this possibility to demonstrate that an std::vector can be treated very much like a static array. (the C++ standard even guarantees that the elements are laid out continuously in memory). But I recommend you use the range-based for-loop that 2kaud suggests. It uses iterators behind the scene but you don't have to deal with them explicitly which is a blessing (*).

---

(*) Because iterators really are pointers in disguise and thus inherently unsafe. Therefore many in the C++ community are eagerly awaiting the Range concept that will further push iterators into the background. One first step in this trend already available is the range-based for-loop.

[Richard.J]

If you want to stick to the iterator approach:

for (BriteNodeInfoList::iterator it = m_briteNodeInfoList.begin(), endIt = m_briteNodeInfoList.End(); it != endIt; ++it)
{
    os << it->nodeId << "\t" << "\t" << it->yCoordinate << "\t" << it->xCoordinate << "\n";
}

and better with "auto"

for (auto it = m_briteNodeInfoList.begin(), endIt = m_briteNodeInfoList.End(); it != endIt; ++it)