In c++ what does this piece of code do?

1

In lot of editorials i have seen this
#ifndef ONLINE_JUDGE

freopen("input.txt", "r", stdin);

freopen("output.txt", "w", stdout);

freopen("error.txt", "w", stderr);

#endif
2

It is for writing input output on file.

3

but how it is beneficial ,as code will accept input and provide output without this also .
i want to know how it will help us in competitive programming with online compiler

4

This useful when you are debugging ie you want to see output for large no of inputs

5

sorry but can you please explain how can i do it
actually i am new to programming world and i want to use this

6

Read about file handling