crash on a vector of vector only after a clear

I've a problem with this code: it crashes always but when I comment: dataResults[i].clear();

Any idea about the reason?

std::vector<std::string> r_OCRtoRetrieve;
std::vector<std::string> DBentries;

//stuff..

int distance = 9999; //TODO change here
int minDistance = 9999;

for(int i=0; i< r_OCRtoRetrieve.size(); i++)
    for(int j=0; j< DBentries.size(); j++)
    {
        distance = calcDistance( (const char *)r_OCRtoRetrieve[i].c_str(),(const char *) DBentries[j].c_str());

        if (distance == minDistance)
            dataResults[i].push_back(DBentries[j]);
        else
            if(distance < minDistance)
            {
                minDistance = distance;
                dataResults[i].clear();
                dataResults[i].push_back(DBentries[j]开发者_如何学Python);
            }

    }

Edit:

Found the error.. I had to initialize it.. here it is the code:

  for(int i=0; i< r_OCRtoRetrieve.size(); i++)
  {
    dataResults.push_back(std::vector<std::string>());

    for(int j=0; j< DBentries.size(); j++)
    {
      distance = calcDistance( (const char *)r_OCRtoRetrieve[i].c_str(),(const char *) DBentries[j].c_str());

      if (distance == minDistance)
    dataResults[i].push_back(DBentries[j]);
      else
    if(distance < minDistance)
    {
      minDistance = distance;
      if(dataResults[i].size() > 0)
        dataResults[i].clear();

      dataResults[i].push_back(DBentries[j]);
    }
    }

  } 

probably, the size of your vector dataResults is smaller than a certain value of i

If you're getting an index out of range exception it's probably because your index i is out of range of the vector dataResults

If that wasn't obvious enough basically if i is greater than dataResults.size() then dataResults[i].clear(); will throw an exception.

Edit:

Consider replacing your index based loops with STL iterators and replacing your c-style casting with C++ style casting. Your if statement could be revisited as well ...

Edit 2:

Was a guessing at a likely problem as you didn't tell us what the exception was but you have a vector<vector<string>> right? If so you need to check what you are indexing into a valid position before calling methods or construct your loop so that it will not index out of bounds.

Something like so:

if (dataResults.size() > i)
{
   // now we know dataResults[i] will be valid
   dataResults[i].clear();
   // etc
}

Honestly I'd probably do something more along the lines of this:

    typedef std::vector<std::string> StrArray;
    for(StrArray::const_iterator ret(r_OCRtoRetrieve.begin()); ret != r_OCRtoRetrieve.end(); ++ret)
    {
        // ret will be an const iterator to each string element in r_OCRtoRetrieve
        for(StrArray::const_iterator entry(DBentries.begin()); entry != DBentries.end(); ++entry)
        {
            // entry will be an const iterator to each string element in DBentries
            distance = calcDistance(ret->c_str(), entry->c_str());

            // init new StrArray in dataResults as needed
            // set new min distances as needed
            // push back strings to dataResults
            // whatever else you want to do
            // yata yata
        }
}

What is in DataResults when you start? Anything? If not, then then the first time through, when distance is anything less than 9999 then the code will attempt to clear a nonexistent location at the first, zeroth index and complain.

If you do a debug build, you should get a meaningful message.