std::out_of_range during std::sort with custom comparator

Question

I have the following code

template<typename T>
bool GenericCompare(T lhs, T rhs)
{
    return lhs < rhs;
}


template<typename T>
class SortOrder
{
public:

    SortOrder(const std::vector<T> *_sortArray, 
              bool (*_comparator)(T,T) = GenericCompare) : 
    sortArray(_sortArray) , comparator (_comparator) , customOperator(true) {;}

    bool operator()(int lhs=0, int rhs=0) const
    {

        bool res;

        try {
             sortArray->at(lhs);

        }
        catch (std::out_of_range& oor) {
            std::cout << "LHS Out of range: " << lhs << " : " << rhs 
                      << " " << oor.what() << std::endl;
        }
        try {
            sortArray->at(rhs); 
        }
        catch (std::out_of_range& oor) {
            std::cout << "RHS Out of range: " << lhs << " : " 
                      << rhs << " "<< oor.what() << std::endl;

        }
        // Always needs comparator
        res = comparator(sortArray->at(lhs),sortArray->at(rhs));    
        return res;

    }
    private:
    const std::vector<T> *sortArray;
    bool (*comparator)(T,T);
    bool customOperator; 
    };

Now I have a simple sorting code in which I sort an index vector based on another vector which is a double. 'circle_fwd_vector' is a vector containing all doubles.

for (int i=0;i<circle_fwd_vector.size();i++) {
  circle_index_vector.push_back(i); 
}
try {
  std::sort(circle_index_vector.begin(),circle_index_vector.end(),
            SortOrder<double>(&circle_fwd_vector));
}
catch (std::exception& e)
{
  std::cout << e.what() << std::endl;
}

Now in the console, I'm getting a result like this:

 RHS Out of range: 1711 : 1079615151 vector::_M_range_check

Since I'm not using any custom class and the vector I'm sorting is based on just doubles I'm not sure why I am getting this out of range. I made sure there are no infinities in the double vector, but even if there are, shouldn't std::sort still give me the correct sorted index without going out of index?

Thank you for any help.

Edit: If it helps, here is the data dump of the vector when this happens. http://pastebin.com/7wLX63FJ Also, I'm compiling this using GCC 4.2 that ships with Xcode 3.2.6.

Answer 1

This error is caused by the nan value in your data (position 1688). The problem is that < is no longer satisfies the constraints required by std::sort when you include nans. See the standard, 25.4/4, for the definition of the "strict weak ordering" that all comparators have to satisfy.