Converting std::string to uint32_t

Question

I have a string like below:

std::string strl="ffffffffffffffffffffffffffffffffffffffffffff";

I want to convert it into uint32_t variable like below:

uint32_t val = std::stoul(strl, nullptr, 16);

The above operation gives a "SIGABRT" signal and gives error:

terminate called after throwing an instance of 'std::out_of_range'
what():  stoul.

What changes to be done for resolving the issue or it is not possible with uint32_t datatype to store the string.

Answer 1

uint32_t can only store up to 0xffffffff as it's a 32 bit unsigned type, so it's not possible to store your string with that data type.

For the string you present, you'll need a big integer library to parse it.

Boost has a good one, and even includes typedefs like uint1024_t, so it's very simple to use.

See http://www.boost.org/doc/libs/1_58_0/libs/multiprecision/doc/html/index.html

Answer 2

If you really want to store the number in a uint32_t, you'll need to validate it.

I would approach it something like this:

#include <string>
#include <cstdint>
#include <stdexcept>
#include <iostream>

auto parse_hex_uint32(std::string const& input) -> std::uint32_t
try
{
    std::size_t read_len = 0;

    auto initial_result = std::stoull(input, &read_len, 16);
    if (read_len != input.size())
    {
        throw std::runtime_error("invalid input: " + input);
    }
    if (initial_result > std::numeric_limits<std::uint32_t>::max())
    {
        throw std::out_of_range("number too large: " + std::to_string(initial_result));
    }

    return std::uint32_t(initial_result);
}
catch(...)
{
    std::throw_with_nested(std::runtime_error("failed to parse " + input + " as hex uint32"));
}

void print_exception(const std::exception& e, int level =  0)
{
    std::cerr << std::string(level, ' ') << "exception: " << e.what() << '\n';
    try {
        std::rethrow_if_nested(e);
    } catch(const std::exception& e) {
        print_exception(e, level+1);
    } catch(...) {}
}

int main()
{
    using namespace std::literals;
    auto input = "ffffffffffffffff"s;
    try
    {
        std::cout << parse_hex_uint32(input) << std::endl;
        return 0;
    }
    catch(std::exception& e)
    {
        print_exception(e);
        return 100;
    }
}