How to read and write to a text file in C++?

Header files needed:

#include <iostream> #include <fstream> 

declare input file stream:

ifstream in("in.txt"); 

declare output file stream:

ofstream out("out.txt"); 

if you want to use variable for a file name, instead of hardcoding it, use this:

string file_name = "my_file.txt"; ifstream in2(file_name.c_str()); 

reading from file into variables (assume file has 2 int variables in):

int num1,num2; in >> num1 >> num2; 

or, reading a line a time from file:

string line; while(getline(in,line)){ //do something with the line } 

write variables back to the file:

out << num1 << num2; 

close the files:

in.close(); out.close(); 

Default c++ mechanism for file IO is called streams. Streams can be of three flavors: input, output and inputoutput. Input streams act like sources of data. To read data from an input stream you use >> operator:

istream >> my_variable; //This code will read a value from stream into your variable. 

Operator >> acts different for different types. If in the example above my_variable was an int, then a number will be read from the strem, if my_variable was a string, then a word would be read, etc. You can read more then one value from the stream by writing istream >> a >> b >> c; where a, b and c would be your variables.

Output streams act like sink to which you can write your data. To write your data to a stream, use << operator.

ostream << my_variable; //This code will write a value from your variable into stream. 

As with input streams, you can write several values to the stream by writing something like this:

ostream << a << b << c; 

Obviously inputoutput streams can act as both.

In your code sample you use cout and cin stream objects. cout stands for console-output and cin for console-input. Those are predefined streams for interacting with default console.

To interact with files, you need to use ifstream and ofstream types. Similar to cin and cout, ifstream stands for input-file-stream and ofstream stands for output-file-stream.

Your code might look like this:

#include <iostream> #include <fstream> using namespace std; int start() { cout << "Welcome..."; // do fancy stuff return 0; } int main () { string usreq, usr, yn, usrenter; cout << "Is this your first time using TEST" << endl; cin >> yn; if (yn == "y") { ifstream iusrfile; ofstream ousrfile; iusrfile.open("usrfile.txt"); iusrfile >> usr; cout << iusrfile; // I'm not sure what are you trying to do here, perhaps print iusrfile contents? iusrfile.close(); cout << "Please type your Username. \n"; cin >> usrenter; if (usrenter == usr) { start (); } } else { cout << "THAT IS NOT A REGISTERED USERNAME."; } return 0; } 

For further reading you might want to look at c++ I/O reference

To read you should create an instance of ifsteam and not ofstream.

ifstream iusrfile; 

You should open the file in read mode.

iusrfile.open("usrfile.txt", ifstream::in); 

Also this statement is not correct.

cout<<iusrfile; 

If you are trying to print the data you read from the file you should do:

cout<<usr; 

You can read more about ifstream and its API here