C++ "random" string

RandomString.hpp

#pragma once

#include <random>
#include <string>
#include <ctime>

namespace RandomString {

static constexpr const char* DEFAULT_CHARSET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
static std::default_random_engine random{static_cast<unsigned>(time(0))};
static std::mt19937 random_generator(random());

std::string generate(size_t length, const std::string& charset = "") {
	// use default charset if no charset is specified
	std::string str = charset.empty() ? std::string(DEFAULT_CHARSET) : charset;

	// double string length until it is at least as long as the requested length
	while(length > str.length()) str += str;

	// shuffle string
	std::shuffle(str.begin(), str.end(), random_generator);

	// return substring with specified length
	return str.substr(0, length);
}
	
} // namespace RandomString