ofSort: not properly working?

I’m trying to use the function ofSort to order a vector.

To learn how does it work I’ve try to create an example to sort and int vector. I write the code below.

In testApp.h

vector<int>::iterator it;  
bool ordina(int &a, int &b);  
vector<int> numbers;  

In testApp.cpp:

void testApp::setup(){  
    it = numbers.begin();  
    while(it != numbers.end()){  
        cout << *it;  

And a function to order called “ordina”:

bool testApp::ordina(int &a, int &b){  
    return a<b;  

When I try to compile the code, I have this error:
C:\Program Files (x86)\CodeBlocks\of\apps\myApps\Vector\src\testApp.cpp|18|error: no matching function for call to ‘ofSort(std::vector&, )’|

I don’t understard where is the error, I consulted also this example: https://github.com/openframeworks/openFrameworks/pull/965/files

Thanks if someone can halp me.

it works if I declare a function directly in testApp.ccp before the “testApp::setup” function for example called “ordina”:

bool ordina(const int &a, const int &b){  
  return a<b;  

and in the “ofSort” function i call the following function:

ofSort(numbers, ordina);  

Thanks if someone can help me understand the problem.