Primes Class

[Browni3141]

I can't seem to get my friend function to work. I looked at the tutorial and I think I got the syntax correct, but I'm getting this compiler error:
59 `plist' undeclared (first use this function)
Doesn't the function have access to private members?

Here's the header:

#ifndef __PRIMES_HPP
#define __PRIMES_HPP

#include <vector>
#include <string>

class primes
{
    public:
	//constructors
	primes(int);
	primes(char*, int);
	primes(std::string, int);
	//public member functions
	friend bool ptest(uint64_t);//
        int operator [] (int);
        int at(int);
        int size();
        int back();
    private:
	std::vector <int> plist;
};

#endif 

And the implementation:

#include "primes.hpp"
#include <fstream>
#include <vector>
#include <cmath>
#include<iostream>

primes::primes(int size)
{
	std::vector <bool> sieve(size);
	for (int i = 2; i < size; i++)
		if (!sieve[i])
		{
			plist.push_back(i);
			for (int j = 1; i*j < size; j++)
				sieve[i*j] = 1;
		}
}

primes::primes(char *filename, int size)
{
	std::ifstream in(filename);
	if (!in)
	{
		std::cout << "Error opening file.\nFile \'" << filename << "\' may not exist.\n";
		std::cin.get();
	}
	int temp;
	in >> temp;
	while (temp < size)
	{
		plist.push_back(temp);
		in >> temp;
	}
}

primes::primes(std::string filename, int size)
{
	primes(filename.c_str(), size);
}

int primes::operator [] (int index)
{
	return plist[index];
}

int primes::at(int index)
{
	return plist.at(index);
}

int primes::back()
{
	return plist.back();
}
        
bool ptest(uint64_t number)//this function was declared friend
{
	for (int i = 0; plist[i] <= sqrt(number); i++)//is sqrt() bad?
		if (number%plist[i] == 0)
			return false;
	return true;
}

[webJose]

it should be bool primes::ptest(uint64_t number) and there is no need for friend. ptest() is just another member function, just like at() or back().

[Azagaros]

Friend functions don't have normal scope rules for accessing the class. You need to have the Class represented in the function's arguments and access it through there...

for example:

// the friend function.
CString operator+(char *pString, CString &cStr)
//                ^working variable...
//                                     ^the class reference.
{
    // CString =
    int nLen = strlen(pString)+strlen(cStr.c_str()) +1;
    CString strTmp;
    delete [] strTmp.m_pString;
    strTmp.m_pString = new char[nLen];
    strcpy(strTmp.m_pString, pString);
    strcpy(strTmp.m_pString, cStr.c_str());
    return strTmp;
    // friend function...
}