How to Parse Integers from a Text File in C with ifstream?

Parsing Integers from a Text File in C Using ifstream

In the realm of programming, working with files is a common necessity. One such task involves reading integers from a text file for data analysis or graph construction. Yet, when faced with a text file containing an unknown number of lines, each consisting of a varying number of integers, parsing becomes a challenge.

To address this problem, we can employ the trusty ifstream class and std::getline() function to read lines from the text file. However, line parsing poses a new hurdle. To overcome this, let us delve into two effective approaches:

Using StringStream and While Loop:

This method utilizes the istringstream constructor to parse a line. It reads integers within a while loop, appending them to a vector until newline is encountered:

<code class="cpp">while (std::getline(infile, line))
{
  std::istringstream iss(line);
  int n;
  std::vector<int> v;

  while (iss >> n)
  {
    v.push_back(n);
  }

  // Utilize the parsed integer vector 'v' for your desired purpose
}</code>

One-Line Solution with std::move:

For a more streamlined approach, we can employ a combination of std::move() and a for loop:

<code class="cpp">for (std::string line;
     std::getline(std::cin, line);
     vv.push_back(std::vector<int>(std::istream_iterator<int>(std::stay(std::istringstream(line))),
                                 std::istream_iterator<int>()))
    ) { }</code>

This solution utilizes the std::stay() function to retain ownership of the input stream, enabling use within the for loop. It iterates over the lines, using std::istream_iterator to parse integers into vector>.

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