Name output file by taking cin by the user - c++

Question

Following is the code to have output file. What if I want to give this output file different name each time, i.e., as demanded by the user. What kind of getline command would help.
I know I can simply cin a string name my_file but the desired name is in the input not in the string name.
void save(cdStruct *ptr) //Function that saves database info to file
{
ofstream dataFile;
dataFile.open("output.txt", ios::out | ios::app);
dataFile << ptr->title << endl;
dataFile << ptr->artist << endl;
dataFile << ptr->numberOfSongs << endl;
dataFile << ptr->number << endl;
dataFile.close();
}

Answer 1

You want to change this line:
dataFile.open("output.txt", ios::out | ios::app);
To something like this??
dataFile.open(my_name_string, ios::out | ios::app);
If yes, you have only to read this string before, add ".txt" and it's everything.
Check this code:
string name;
cin >name;
name.append(".txt");
ofstream dataFile;
dataFile.open(name.c_str(), ios::out | ios::app);
dataFile.close();

Answer 2

From your comments on other answers it sounds like you are passing the file name as a std::string to std::ofstream::open. Before C++11 it only accepted a const char * parameter, not a std::string (see this reference).
To fix this use filename.c_str() as the first parameter instead of filename. This returns a null-terminated char array, the type expected by std::ofstream::open

Answer 3

Your error message tells the following: you are using std::string at some point when you should be using char const *. Now we only need to find the proper place where the error occurs.
A quick look into online documentation of std::getline tells us, that this function is not the problem: the signature allows std::string. The only other thing that has changed is the std::ofstream(filename, std::ios::out | std::ios::ate), so we check the documentation of std::ofstream; indeed a char const *.
This problem should be quickly solved by replacing
std::ofstream dataFile(filename, std::ios::out | std::ios::ate);
with
std::ofstream dataFile(filename.data(), std::ios::out | std::ios::ate);
and then it should compile.
It is very important that you try to understand the error messages that your compiler is giving you and search for references where the problem may lie.

Answer 4

Your specific problem is not "Give output file desired name as desired by the user", but "How to read user input in command line program". For this, you can use std::getline:
#include <iostream>
#include <string>
int main() {
std::string filename;
getline(std::cin, filename);
}
One could be tempted to use the operator<< overloads,
#include <iostream>
#include <string>
int main () {
std::string filename;
std::cin >> filename;
}
however, they would give wrong results if your filename contains whitespace characters.
Sidenote: Don't pass nullable pointers when you want to enforce non-null values:
// don't: void save(cdStruct *ptr)
void save(cdStruct const &ptr) // <- ah, better