How to use std::transform() function - c++

Question

Ok basically i need to use the std::transform() function. I am trying however to pass an object function in as the last argument though and it doesnt seem to work.
class isprime {
public:
// declares the constructor and the operator() overloading
isprime(){ number = 0, primes.push_back(2);};
bool operator()(int);
private:
// various private functions and variables
int number;
list<int> primes; //creats a list via the stl library
void morePrimes(int); //function to generate more prime numbers
bool it; // Iterator for the morePrimes list
bool primeCheck; // Bool used in the morePrimes function
};
bool isprime::operator()(int number)
{
if(number == 1) //returns false for 1
return false;
if(number > primes.back()){ //Tests to see if the list of primes range would include the number, if not it runs the morePrimes function
morePrimes(number);
}
it = binary_search(primes.begin(),primes.end(),number); //uses stl find to see if the number is in the list of primes.
if(it) //if the returned iterator points to a value = to number then number is prim.
return true;
return false; //returns false if the number wasnt found
};
transform(random_list.begin(), random_list.end(), isprime_list.begin(), test());
Above i have included the class, the function and the call i used for transform. Anyone know why this doesnt work? I cant figure it out.

Answer 1

If you provide void isprime::more_primes(int) somewhere, removing the parentheses in test() is likely enough:
int main()
{
auto gen = bind(uniform_int_distribution<>(), mt19937());
list<int> random_list;
for (int i=0; i<5; i++) random_list.push_back(gen());
list<int> isprime_list(random_list.size());
isprime test;
transform(random_list.begin(), random_list.end(), isprime_list.begin(), test);
}
See it 'running' (well, compiling) on Coliru: http://coliru.stacked-crooked.com/a/3d908cb5cdc5c543
#include <list>
#include <algorithm>
using namespace std;
class isprime {
public:
// declares the constructor and the operator() overloading
isprime(){ number = 0, primes.push_back(2);};
bool operator()(int);
private:
// various private functions and variables
int number;
list<int> primes; // creats a list via the stl library
void morePrimes(int); // function to generate more prime numbers
bool it; // Iterator for the morePrimes list
bool primeCheck; // Bool used in the morePrimes function
};
bool isprime::operator()(int number)
{
if(number == 1) // returns false for 1
return false;
if(number > primes.back()){ // Tests to see if the list of primes range would include the number, if not it runs the morePrimes function
morePrimes(number);
}
it = binary_search(primes.begin(),primes.end(),number); // uses stl find to see if the number is in the list of primes.
if(it) // if the returned iterator points to a value = to number then number is prim.
return true;
return false; // returns false if the number wasnt found
}
void isprime::morePrimes(int) {}
#include <random>
#include <functional>
#include <iostream>
#include <iterator>
int main()
{
auto gen = bind(uniform_int_distribution<>(), mt19937());
list<int> random_list;
for (int i=0; i<5; i++) random_list.push_back(gen());
list<int> isprime_list(random_list.size());
isprime test;
transform(random_list.begin(), random_list.end(), isprime_list.begin(), test);
}