function object, function pointer and function.

["learning c++" <learning_c@xxxxxxxxxxx>]

Hi, Everyone:

I compiled a short code that invovles function object and function pointer.

in the line:  int count1 = count_if(v1.begin(), v1.end(), 
&lessThan20Function);

I used the funtion poiter to pass the address of function. It works very 
well,

However, when I deleted the symbol "&", it still works. "lessThan20Function" 
is the name of function. Can we use the function name as an argument?

What is the advantage of function object?

Thanks in advanace!

#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;

bool lessThan20Function(int value)
{
   return value < 20;
}

class LessThan20 {
public:
   bool operator() (int value) const
   {
       return value < 20;
   }
};

int main() {

   int iarr[10] = {2,4,55,6,66,10,22,14,70,1234};
   vector<int> v1(iarr, iarr+10);

   LessThan20 lt20;
   // count_if(start_iterator, end_iterator, predicate);

   // Pointer to a function as argument
   int count1 = count_if(v1.begin(), v1.end(), &lessThan20Function);
   cout << "There are " << count1 << " values less than 20" << endl;

   // Function object as argument
   int count2 = count_if(v1.begin(), v1.end(), lt20);
   cout << "There are " << count2 << " values less than 20" << endl;
   return 0;
]

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