Best way to input/output data from file in C++?

Question

I need a way to read input data which can

1. read until end of file (int variables).

2. read until end of line (int variables).

   example input file :

   1 2 3 4

   3 2 3

   I need :

   Put all numbers in line 1 to first array.

   Put all numbers in line 2 to second array.

3. can use for online compiler : ideone, codeforces,...

4. can read from file.

and a way print output which can

1. print double with two decimal numbers double i = 1.2355 ; print 1.24
2. can use for online compiler

And the most important things is speed. And simple to use.

Which should i use and how to use it ?

Answer 1

For learning C++, I recommend a book like The C++ Programming Language (4th Edition) and A Tour of C++, the latter of which is meant to be a reference for the standard library. There are many facilities in the standard library such as streams and containers which are designed to be easy to use. They also tend to be more efficient than homebrew solutions, but that is a quality of implementation issue.

• For reading files, use std::fstream.
• If possible, avoid arrays and use std::vector.
• To affect the output of floating point numbers, use std::fixed and std::setprecision, i.e. std::cout << std::fixed << std::setprecision(2) << 1.23455;. This does not round. You may refer to Rounding Number to 2 Decimal Places in C for this purpose.