std::sort using member function in the same class? - class

Question

I have a class "PclProc" and I want to use std::sort.
I write a compare function in the same class because this comparing need the "in_ptr" which is a variable in the same class.
But as I did as following, there is always an error:
error: no matching function for call to
‘sort(std::vector::iterator, std::vector::iterator,
)’
std::sort(cloud_indice.indices.begin(),cloud_indice.indices.end(),PclProc::MyCompare);
bool PclProc::MyCompare(int id1, int id2)
{
return in_ptr->points[id1].z<in_ptr->points[id2].z;
}
float PclProc::MedianZDist(pcl::PointIndices cloud_indice)
{
std::sort(cloud_indice.indices.begin(),cloud_indice.indices.end(),PclProc::MyCompare);
int size=cloud_indice.indices.size();
float median_x,median_y;
...

Answer 1

Example of a functor being used for std::sort. vector D is the data, vector I is the indices to D. I is sorted according to D with std::sort using the functor. std::sort only creates one instance of class lessthan, then uses that one instance for all of the compares.
#include <algorithm>
#include <cstdlib>
#include <iostream>
#include <iomanip>
#include <vector>
typedef unsigned int uint32_t;
#define SIZE 16
class example{
public:
std::vector<uint32_t> D; // data
std::vector<uint32_t> I; // indices
example(void)
{
D.resize(SIZE);
I.resize(SIZE);
for(uint32_t i = 0; i < SIZE; i++){
D[i] = rand()%100;
I[i] = i;
}
}
void displaydata(void)
{
for(size_t i = 0; i < SIZE; i++)
std::cout << std::setw(3) << D[I[i]];
std::cout << std::endl;
}
class lessthan // lessthan functor for std::sort
{
public:
const example &x;
lessthan(const example &e ) : x(e) { }
bool operator()(const uint32_t & i0, const uint32_t & i1)
{
return x.D[i0] < x.D[i1];
}
};
void sortindices(void)
{
std::sort(I.begin(), I.end(), lessthan(*this));
}
};
int main()
{
example x;
x.displaydata();
x.sortindices();
x.displaydata();
return 0;
}