Base64 class c++

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <iomanip>
#include <sstream>
#include <cstring>

using namespace std;
class Base64Decoder {
private:
    static constexpr const char* base64_chars =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        "abcdefghijklmnopqrstuvwxyz"
        "0123456789+/";

public:

    static std::string base64_to_hex(const std::string& base64_input) {
        std::vector<unsigned char> decoded_bytes;
        int val = 0, valb = -8;

        for (unsigned char c : base64_input) {
            if (c == '=') break;
            const char* pos = std::strchr(base64_chars, c);
            if (pos == nullptr) continue; // Ignorar caracteres no válidos
            val = (val << 6) + (pos - base64_chars);
            valb += 6;
            if (valb >= 0) {
                decoded_bytes.push_back(char((val >> valb) & 0xFF));
                valb -= 8;
            }
        }

        std::stringstream hex_stream;
        hex_stream << std::hex << std::setfill('0');
        for (unsigned char byte : decoded_bytes) {
            hex_stream << std::setw(2) << static_cast<int>(byte);
        }

        return hex_stream.str();
    }

    // conversion  chaîne hexadécimale en base64  p.e '060200000000' ->BgIAAAAA
    // Fonction pour convertir une chaîne hexadécimale en  vector bytes
    std::vector<uint8_t> hex_string_to_vector(const std::string& hex_string) {
        std::vector<uint8_t> bytes;

        for (size_t i = 0; i < hex_string.length(); i += 2) {
            std::string byteString = hex_string.substr(i, 2);
            uint8_t byte = (uint8_t) std::stoi(byteString, nullptr, 16);
            bytes.push_back(byte);
        }

        return bytes;
    }
};



int main() {
    //Lire entree Base64
    /*
    std::string base64_input;
    std::cout << "Entrez la chaîne Base64: ";
    std::cin >> base64_input;
    */
    string base64_input="BQAA";

    Base64Decoder base64;//Instance Base64Decoder
    string hex_string = base64. base64_to_hex(base64_input);//Base64 to HexString

    cout <<base64_input<<" : "<<hex_string<<endl;//Debug

    //Création d'un vecteur hexadécimal uint_8
    std::vector<uint8_t> vector_hex;
    vector_hex =base64.hex_string_to_vector(hex_string);//Conversion string hex to vector uint_8

    for (uint8_t const & elem:vector_hex){
        cout << "-> 0x" << std::hex << std::setw(2) << std::setfill('0') << static_cast<int>(elem) << std::dec << endl;
    }

    return 0;
}