You can use the bitset member to_ulong to make the conversion.
Code:
#include <iostream>
#include <string>
#include <vector>
#include <bitset>
using namespace std;
int main()
{
string pizza("CHEESE");
vector < bitset<8> > b;
for (int i=0; i<pizza.length(); i++)
b.push_back(pizza[i]);
for (int i=0; i<b.size(); i++)
cout << b[i] << endl;
string pizza_name;
for (int i=0; i<b.size(); i++)
{
char c = b[i].to_ulong();
//cout << (int) c << endl;
pizza_name = pizza_name + c;
}
cout << pizza_name << endl;
}