Получение данных из файла

#include <iostream>
#include <string>
#include <fstream>
#include <cstdlib> //для exit(EXIT_FAILURE)
 
using namespace std;
 
struct patron {
    string name;
    double donation;
};
 
int main()
{
    string filename;
fstream file;
    cout << "Enter name of the file: ";
    getline(cin, filename);
    file.open(filename); //вот здесь ругается
    if (!file.is_open())
    {
        cout << "Could not open the file" << filename << "." << endl;
        exit(EXIT_FAILURE);
    }
    int n;
    (file >> n).get();
    patron * p_patron = new patron[n];
    cout << "Reading the information about patrons." << endl;
    for (int i = 0; i < n; i++)
    {
     cout << "Maecenas  #" << i+1 << endl;
       cout << "Enter name " << endl;
        getline(file, p_patron[i].name);
        cout << "and the amount of donations " << endl;
        (file >> p_patron[i].donation).get();
    }
    file.close();
    
    cout << "Grand Patrons." << endl;
    int countgp = 0;
    for (int j = 0; j < n; j++)
    {
        if (p_patron[j].donation >= 10000)
        {
            cout << p_patron[j].name << " - " << p_patron[j].donation << endl;
            countgp++;
        }
    }
    if (countgp == 0)
        cout << "none" << endl;
    cout << endl;
    cout << "Patrons." << endl;
    int countp = 0;
    for (int k = 0; k < n; k++)
    {
        if (p_patron[k].donation < 10000)
        {
            cout << p_patron[k].name << " - " << p_patron[k].donation << endl;
            countp++;
        }
    }
    if (countp == 0)
        cout << "none" << endl;
    
    cin.get();
    return 0;
}

[Error] no matching function for call to 'std::basic_fstream<char>::open(std::string&)'
 [Note] candidate is:
 [Note] void std::basic_fstream<_CharT, _Traits>::open(const char*, std::ios_base::openmode) [with _CharT = char; _Traits = std::char_traits<char>; std::ios_base::openmode = std::_Ios_Openmode]
 [Note] no known conversion for argument 1 from 'std::string {aka std::basic_string<char>}' to 'const char*'

file.open(filename.c_str());