I'm starting to write C++ and I'm trying to read a text file that is formatted like this:
32.0 12.43
503.2 3.212
etc.
In Java, I could use a Scanner with .nextFloat(), and put the contains into an Array. I am trying to achieve the same thing with C++. How is this done?
To read from standard input
#include <iostream>
int main()
{
float f1, f2, f3, f4;
std::cin >> f1 >> f2 >> f3 >> f4;
}
To read from a file
#include <fstream>
int main()
{
std::ifstream fin("file.txt"); //fin is an arbitrary identifier
float f1, f2, f3, f4;
fin >> f1;
fin >> f2;
fin >> f3;
fin >> f4; // or fin >> f1 >> f2 >> f3 >> f4; no difference
}
To read all floats into an array (vector) of floats, you can use this:
#include <fstream>
#include <vector>
#include <iterator> //for istream_iterator and back_inserter
#include <algorithm> //for copy
int main()
{
std::ifstream fin("input.txt");
std::vector<float> v; //could also initialize with the two-iterator constructor
std::copy(std::istream_iterator<float>(fin),
std::istream_iterator<float>(),
std::back_inserter(v)); //push_back into vector
}
Read more about stream input/output here and elsewhere. I would also strongly advise that you read a good C++ book
C++ has many good native options to read data, e.g., std::cin for user input data and std::ifstream for files. But if you are looking for a quite similar implementation of Java Scanner you can find it in the open source project called Scanner++: http://sourceforge.net/projects/scannerpp/
Many good features of Java Scanner class are implemented there, including the nextFloat() method.
#include "Scanner.h"
using namespace scannerpp;
int main()
{
// to work with strings
Scanner scanner("32.0 12.43 \n 503.2 3.212");
float x = scanner.nextFloat();
// to work with files
Scanner scanner(new File("test-data.txt"));
float x2 = scanner.nextFloat();
}
Hope this helps!
DISCLAIMER: I'm co-author of Scanner++ project.
You can build a String Tokenizer using string::find() or use strtok() or use Boost Tokenizer. I don't know of a pre-existing Scanner equivalent.
Also look at this thread: Converting from Java to C++ Reading a File, and parsing
