Encoding and Decoding Base64 string using Libcodium C library in C++

Libsodium Base64 encode and Decode in C++

``
//
// Created by Razak Zakari on 12/04/2018.
//

#define BASE64_VARIATION sodium_base64_VARIANT_ORIGINAL

#include <algorithm>
#include <math.h>
#include <vector>
#include "crypt.h"

extern "C" {
    #include <sodium.h>
}


/**
 * hidden fun, base64encode
 */
 std::string base64_encode(std::string bin_str){

    //bytes len
    const size_t bin_len = bin_str.size();

    //base64_max_len
    const size_t  base64_max_len = sodium_base64_encoded_len(bin_len,BASE64_VARIATION);

    //std::cout << base64_max_len << std::endl;

    //base64 encoded var
    std::string base64_str(base64_max_len-1,0);

   char * encoded_str_char = sodium_bin2base64(
            base64_str.data(),
            base64_max_len,
            (unsigned char *) bin_str.data(),
            bin_len,
            BASE64_VARIATION
    );

   if(encoded_str_char == NULL){
       throw "Base64 Error: Failed to encode string";
   }

   //std::cout << sizeof(encoded_str_char) << "---" << base64_str.size() << std::endl;

    return base64_str;
 }//end
``

where is here decode base64?