C++ thing for converting the indentation scale of a file

convert_indents.cpp

#include <iostream>
#include <fstream>
#include <vector>
#include <cstring>

int main(int argc, char* argv[]) {
  std::ifstream open_file;
  std::ofstream output;

  if (argc != 3) {
    std::cerr << "Error: Please provide 2 arguments" << std::endl;
    return -1;
  }

  const std::string fname = argv[1];
  const std::string indents_str = argv[2];

  if (indents_str.find_first_not_of("0123456789") != std::string::npos) {
    std::cerr << "Error: Argument 2 must be of type <unsigned integer>" << std::endl;
    return -1;
  }

  const int indents = std::stoi(argv[2]);

  std::vector<std::string> lines;

  open_file.open(fname);

  if (!open_file) {
    return -1;
  }

  std::string x;
  while (!open_file.eof()) {
    std::getline(open_file, x);
    lines.push_back(x + "\n");
  }

  open_file.close();
  output.open(fname);

  int indent_scale = 0;
  int current_indentation = 0;
  std::string spaces;

  for (std::string line : lines) {

    spaces = "";
    current_indentation = 0;

    for (char &c : line) {
      if (c == ' ') {
        current_indentation++;
      } else {
        break;
      }
    }

    if (indent_scale == 0 && current_indentation != 0) {
      indent_scale = current_indentation;
      std::cout << "Indentation detected as " << indent_scale << std::endl;
    }
    if (indent_scale > 0) {
      int set_to = (((double)current_indentation / (double)indent_scale) * indents);

      std::cout << set_to << std::endl;

      for (int i = 0; i < set_to; i++) {
        spaces += " ";
      }
    }

    std::string a = "";
    bool exited_spaces = false;

    for (char &c : line) {
      if (!exited_spaces && c == ' ') {
        continue;
      } else {
        exited_spaces = true;
        a += c;
      }
    }

    output << spaces << a;
  }

  output.close();

}