test_cmssw40902.cc

#include <charconv>
#include <exception>
#include <iostream>
#include <regex>
#include <string>

// Pre PR
bool isNumber(const std::string &str) {
  static const std::regex re("^[+-]?(\\d+\\.?|\\d*\\.\\d*)$");
  return std::regex_match(str.c_str(), re);
}
double toNumber(const std::string &str) { return atof(str.c_str()); }

// PR 40956
bool toNumber(std::string const& str, double &result) {
  if (str.empty()) {
    return false;
  }
  const char *first = str.c_str();
  const char *last = first + str.size();
  if (*first == '+') {
    ++first;
  }
  const auto [ptr, ec] = std::from_chars(first, last, result);
  return ec == std::errc();// and ptr == last;
}

// main
int main (int argc, char** argv) {

  if (argc != 2) {
    std::cout << "One command-line argument required" << std::endl;
    return 1;
  }

  std::string const str = argv[1];
  std::cout << "String: '" << str << "'" << std::endl;

  {
    std::cout << "=== Pre PR" << std::endl;
    if (isNumber(str)) {
      std::cout << "YES, is number " << toNumber(str) << std::endl;
    }
    else {
      std::cout << "NO, is no number" << std::endl;
    }
    std::cout << "=============" << std::endl;
  }

  {
    std::cout << "=== PR 40915" << std::endl;
    try {
      double const number = std::stof(str);
      std::cout << "YES, is number " << number << std::endl;
    }
    catch (std::exception const& ex) {
      std::cout << "NO, is no number (" << ex.what() << ")" << std::endl;
    }
    std::cout << "=============" << std::endl;
  }

  {
    std::cout << "=== PR 40956" << std::endl;
    double number{};
    if (toNumber(str, number)) {
      std::cout << "YES, is number " << number << std::endl;
    }
    else {
      std::cout << "NO, is no number" << std::endl;
    }
    std::cout << "=============" << std::endl;
  }

  return 0;
}