Generic and safe strtod wrapper for Modern C++

to_floating_point.hpp

/// @file
/// Generic and safe strtod wrapper for Modern C++.

#ifndef TO_FLOATING_POINT_HPP_
#define TO_FLOATING_POINT_HPP_

#include <cwchar>
#include <cctype>
#include <string>
#include <type_traits>

/// Converts the string representation of a number to its floating-point number equivalent.
/// @param str the string containing a number to convert.
/// @tparam TNumber an floating-point number type.
/// @return the floating-point number value equivalent of the number contained in str.
/// @throws std::invalid_argument if str contains an invalid character which cannot be interpreted.
/// @throws std::out_of_range if the converted value would fall out of the range of the result type.
template <typename TNumber>
TNumber to_floating_point(
    const std::string & str) {
  const char * ptr = str.c_str();
  char * endptr;
  errno = 0;
  double ans = std::strtod(ptr, &endptr);

  if (ptr == endptr) {
    throw std::invalid_argument("invalid to_floating_point argument");
  }

  while (*endptr != '\0') {
    if (std::isspace(*endptr) == 0) {
      throw std::invalid_argument("invalid to_floating_point argument");
    }
    ++endptr;
  }

  if (errno == ERANGE ||
      ans < std::numeric_limits<TNumber>::lowest() ||
      ans > std::numeric_limits<TNumber>::max()) {
    throw std::out_of_range("to_floating_point argument out of range");
  }

  return static_cast<TNumber>(ans);
}

/// Converts the string representation of a number to its floating-point number equivalent. A return value indicates whether the conversion succeeded.
/// @param str the string containing a number to convert.
/// @param result an floating-point number variable to store the floating-point number value equivalent of the number contained in str.
/// @tparam TNumber an floating-point number type.
/// @return true if str was converted successfully.
template <typename TNumber>
bool try_parse_floating_point(
    const std::string & str,
    TNumber & result) noexcept {
  const char * ptr = str.c_str();
  char * endptr;
  errno = 0;
  double ans = std::strtod(ptr, &endptr);

  if (ptr == endptr) {
    return false;
  }

  while (*endptr != '\0') {
    if (std::isspace(*endptr) == 0) {
      return false;
    }
    ++endptr;
  }

  if (errno == ERANGE ||
      ans < std::numeric_limits<TNumber>::lowest() ||
      ans > std::numeric_limits<TNumber>::max()) {
    return false;
  }

  result = static_cast<TNumber>(ans);
  return true;
}

/// Converts the string representation of a number to its floating-point number equivalent.
/// @param str the string containing a number to convert.
/// @tparam TNumber an floating-point number type.
/// @return the floating-point number value equivalent of the number contained in str.
/// @throws std::invalid_argument if str contains an invalid character which cannot be interpreted.
/// @throws std::out_of_range if the converted value would fall out of the range of the result type.
template <typename TNumber>
TNumber to_floating_point(
    const std::wstring & str) {
  const wchar_t * ptr = str.c_str();
  wchar_t * endptr;
  errno = 0;
  double ans = std::wcstod(ptr, &endptr);

  if (ptr == endptr) {
    throw std::invalid_argument("invalid to_floating_point argument");
  }

  while (*endptr != L'\0') {
    if (std::isspace(*endptr) == 0) {
      throw std::invalid_argument("invalid to_floating_point argument");
    }
    ++endptr;
  }

  if (errno == ERANGE ||
      ans < std::numeric_limits<TNumber>::lowest() ||
      ans > std::numeric_limits<TNumber>::max()) {
    throw std::out_of_range("to_floating_point argument out of range");
  }

  return static_cast<TNumber>(ans);
}

/// Converts the string representation of a number to its floating-point number equivalent. A return value indicates whether the conversion succeeded.
/// @param str the string containing a number to convert.
/// @param result an floating-point number variable to store the floating-point number value equivalent of the number contained in str.
/// @tparam TNumber an floating-point number type.
/// @return true if str was converted successfully.
template <typename TNumber>
bool try_parse_floating_point(
    const std::wstring & str,
    TNumber & result) noexcept {
  const wchar_t * ptr = str.c_str();
  wchar_t * endptr;
  errno = 0;
  double ans = std::wcstod(ptr, &endptr);

  if (ptr == endptr) {
    return false;
  }

  while (*endptr != L'\0') {
    if (std::isspace(*endptr) == 0) {
      return false;
    }
    ++endptr;
  }

  if (errno == ERANGE ||
      ans < std::numeric_limits<TNumber>::lowest() ||
      ans > std::numeric_limits<TNumber>::max()) {
    return false;
  }

  result = static_cast<TNumber>(ans);
  return true;
}

#endif // !TO_FLOATING_POINT_HPP_