Alter a .txt file of a variable directory

I'm trying to write a program that alters a .txt file of a variable directory. However开发者_开发技巧 when I attempt to do so I get an error.

My error:

no matching function for call to `std::basic_ofstream<char,      std::char_traits<char> >::basic_ofstream(std::string&)' 

My code:

#include <iostream>
#include <fstream>
using namespace std;

int main () {
    string file_name ;
    cout << "Input the directory of the file you would like to alter:" << endl;
    cin >>  file_name ;


    ofstream myfile ( file_name );
    if (myfile.is_open())
    {
    myfile << "This is a line.\n";
    myfile << "This is another line.\n";
    myfile.close();
    }
    else cout << "Unable to open file";
    return 0;

}

What did I do wrong?

The fstream constructors take C strings, not std::string, so you need

std::ofstream myfile(file_name.c_str());

The reason why they take C strings instead of std::strings is purely historical; there's no technical reason. C++0x adds constructors that take std::strings.