Question

In my program written in C++, I open a file as follows:

std::ifstream file("testfile.txt");

This usage can handle the scenario where the input file has a fixed name of “testfile.txt”.
I would like to know how to allow the user to input a file name, e.g., “userA.txt”, and the program automatically opens this file, “userA.txt”.

Answer 1

Use a variable. I suggest finding a good introductory book if you’re not clear on what they are yet.

#include <iostream>
#include <string>

// ...

std::string filename;    // This is a variable of type std::string which holds a series of characters in memory

std::cin >> filename;    // Read in the filename from the console

std::ifstream file(filename.c_str());    // c_str() gets a C-style representation of the string (which is what the std::ifstream constructor is expecting)

If the filename can have spaces in it, then cin >> (which stops input at the first space as well as newline) won’t cut it. Instead, you can use getline():

getline(cin, filename);    // Reads a line of input from the console into the filename variable