string2int.h

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/*******************************************************************\
 
Module:
 
Author: Michael Tautschnig, michael.tautschnig@cs.ox.ac.uk
 
\*******************************************************************/
 
 
#ifndef CPROVER_UTIL_STRING2INT_H
#define CPROVER_UTIL_STRING2INT_H
 
#include "narrow.h"
 
#include <charconv>
#include <optional>
#include <string>
#include <string_view>
#include <type_traits>
 
// These check that the string is indeed a valid number,
// and fail an assertion otherwise.
// We use those for data types that C++11's std::stoi etc. do not
// cover.
unsigned safe_string2unsigned(std::string_view, int base = 10);
std::size_t safe_string2size_t(std::string_view, int base = 10);
 
// The below mimic C's atoi/atol: any errors are silently ignored.
// They are meant to replace atoi/atol.
int unsafe_string2int(const std::string &, int base = 10);
unsigned unsafe_string2unsigned(const std::string &, int base = 10);
std::size_t unsafe_string2size_t(const std::string &, int base = 10);
 
// Same for atoll
long long int unsafe_string2signedlonglong(const std::string &, int base = 10);
long long unsigned int
unsafe_string2unsignedlonglong(const std::string &, int base = 10);
 
// if we had a `resultt` á la Boost.Outcome (https://ned14.github.io/outcome/)
// we could also return the reason why the conversion failed

std::optional<int> string2optional_int(std::string_view, int base = 10);

std::optional<unsigned>
string2optional_unsigned(std::string_view, int base = 10);

std::optional<std::size_t>
string2optional_size_t(std::string_view, int base = 10);

template <typename T>
std::optional<T> string2optional(std::string_view str, int base = 10)
{
  PRECONDITION(base == 2 || base == 8 || base == 10 || base == 16);
 
  static_assert(
    std::is_integral<T>::value, "string2optional requires an integral type");
 
  if(str.empty())
    return std::nullopt;
 
  // reject negative inputs for unsigned types
  if(std::is_unsigned<T>::value && str.front() == '-')
    return std::nullopt;
 
  const char *first = str.data();
  const char *last = str.data() + str.size();
 
  T value{};
  auto [ptr, ec] = std::from_chars(first, last, value, base);
 
  if(ec != std::errc{} || ptr != last)
    return std::nullopt;
 
  return value;
}
 
#endif // CPROVER_UTIL_STRING2INT_H