Random hex string in C++

/* Generate a random hexidecimal string of large number of nibbles.
 * (Created because needed a 204-bit integer.)
 *
 * davep 17-Mar-2015
 */

#include <iostream>
#include <string>
#include <random>
#include <algorithm>
#include <chrono>

using namespace std;

/* With assistance from
 * https://stackoverflow.com/questions/440133/how-do-i-create-a-random-alpha-numeric-string-in-c
 * http://www.cplusplus.com/reference/random/linear_congruential_engine/linear_congruential_engine/
 */
string random_hex_string( size_t length )
{
    unsigned seed1 = chrono::system_clock::now().time_since_epoch().count();
    string charset { "0123456789abcdef" };
    auto gen = bind(uniform_int_distribution<unsigned int>{0,charset.size()-1},
                    default_random_engine{seed1});

    auto randchar = [&charset,&gen]() -> char
    {
        return charset.at(gen());
    };

    string str(length,0);
    generate_n( str.begin(), str.size(), randchar );
    return str;
}

int main()
{
    string str = random_hex_string(51);
    cout << str << '\n';
}