Reading Floats from a txt file in C-CodePudding

I am trying to read (x,y) floating point values from a txt file in C . The numbers are seperated by a space. In the file, The ith number and the i 1st number make the (x,y) coordinates. So index positions 0 and 1 would be one (x,y) pair and index positions (1,2) would be another (x,y) pair.

This is what I have done but I am not sure how I can save them as floats.

 ifstream randomFile;
        string content;
        randomFile.open("random.txt");
        if(randomFile.is_open()) {
            while(getline(randomFile,content)){
            randomFile >> content;
            }
            randomFile.close();
        }

CodePudding user response：

Read the first float x
While additional read y succeeds:
Add (x, y) to your list
x = y

#include <iostream>
#include <vector>

struct xy
{
  float x, y;
  xy( float x, float y ) : x{x}, y{y} { }
};

auto read_xy_pairs( std::istream & ins )
{
  std::vector<xy> xys;
  float x, y;
  ins >> x;
  while (ins >> y)
  {
    xys.emplace_back( x, y );
    x = y;
  }
  return xys;
}

#include <sstream>
#include <string>

int main()
{
  std::cout << "list of numbers? ";
  std::string s;
  getline( std::cin, s );
  std::istringstream numbers( s );
  
  for (auto [x, y] : read_xy_pairs( numbers )) 
    std::cout << "(" << x << ", " << y << ")\n";
}

Example:

list of numbers? 1 2 3 4 5
(1, 2)
(2, 3)
(3, 4)
(4, 5)

CodePudding user response：

An extra variable (prev) can be used to store the value of last input and append (prev,curr) on every iteration to the storage container. In the following code, I have used vector of pairs of float to store the pairs, but you may use arrays or structures as well.

#include<fstream>
#include<iostream>
#include<vector>
using namespace std;

int main() {
    //Declaring vector of float pairs
    vector <pair<float, float>> floatPairs;
    ifstream randomFile;
    float curr, prev;

    randomFile.open("a.txt");
    randomFile >> curr;
    while (!randomFile.eof()) {
        prev = curr;
        randomFile >> curr;

        //Appending to vector of float pairs
        floatPairs.push_back({ prev,curr });
    }

    //Printing
    for (auto i : floatPairs) {
        cout << "(" << i.first << ", " << i.second << ")\n";
    }
}

Input file content: 12.5 56.8 34.7 75.7 23.4 86.7 34.9 66.8

Output:

(12.5, 56.8)
(56.8, 34.7)
(34.7, 75.7)
(75.7, 23.4)
(23.4, 86.7)
(86.7, 34.9)
(34.9, 66.8)