Question

I have a 2D vector and I need to remove blocks that do not contain sufficient values:

typedef vector<double> iniMatrix;


bool hasInsufficientEnergy() {
return true;
}
vector<double> Audio::filter(vector<iniMatrix>&blocks, double sumThres, double ZeroThres)
{
  vector<double> totalEnergy;
  vector<double> totalZeroCross;
  double totalSum = sumThres * blocks.size();
  double totalZero = ZeroThres * blocks.size();

  vector<iniMatrix> blockked;

  for(unsigned i=0; (i < blocks.size()); i++)
  {
    totalEnergy.push_back(abs(this->energy(blocks[i])));
    totalZeroCross.push_back(zerocross(blocks[i]));

    if(!totalEnergy[i] > totalSum || totalZeroCross[i] < ZeroThres)
    {
        hasInsufficientEnergy();
    }else{
        //hasInsufficientEnergy();
    }
    iniMatrix::iterator erase_after = remove_if(blocks[i].begin(), blocks[i].end(),
                                                &hasInsufficientEnergy);
 }
 }

The problem is erase_after and comes up with an error message:

In function ‘_OutputIterator std::remove_copy_if(_InputIterator, _InputIterator, 
 _OutputIterator, _Predicate) [with _InputIterator = __gnu_cxx::__normal_iterator<double*, 
std::vector<double, std::allocator<double> > >, _OutputIterator = 
__gnu_cxx::__normal_iterator<double*, std::vector<double, std::allocator<double> > >, 
_Predicate = bool]’:
/usr/include/c++/4.2.1/bits/stl_algo.h:1302:   instantiated from ‘_ForwardIterator 
std::remove_if(_ForwardIterator, _ForwardIterator, _Predicate) [with _ForwardIterator = 
__gnu_cxx::__normal_iterator<double*, std::vector<double, std::allocator<double> > >, 
_Predicate = bool]’
Audio.cpp:105:   instantiated from here
/usr/include/c++/4.2.1/bits/stl_algo.h:1227: error: ‘__pred’ cannot be used as a function

Anyone have any ideas to where I am going wrong?

Answer 1

true or false aren’t function objects. If you want to use remove_if you must give it a pointer to function or function object, which takes a member of the collection as parameter and returns whether to remove it or not. Look at the example in std::remove_if

AFAICS, you could replace the remove_if/erase into the if and simplify it to:

for(auto i=blocks.begin(); i != blocks.end(); )
{
    totalEnergy.push_back(abs(this->energy(*i)));
    totalZeroCross.push_back(zerocross(*i));

    if(!totalEnergy.rbegin() > totalSum || totalZeroCross.rbegin() < ZeroThres)
    {
        i = blocks.erase(i);
    } else {
        ++i;
    }
}