将setfill和setw的输出存储到字符串中

Question

I am trying to produce binary numbers using C's itoa function and C++ setfill and setw function. If I use only itoa , the output displayed does not have proper 0 padding.

This is a small code snippet.

int s = 8;
for (int i = 1; i<s;i++)
    {
        itoa(i,buffer,2);
        cout<<setfill('0')<<setw(3)<<endl;
        cout<<buffer<<endl;
    }

Now it does a great job in printing out the output.

If I hadn't used setfill and setw, the formatting would have been something like

1
10
11
100
101
110
111

instead of

001
010
011
100
101
110
111

Now I want to store the padded binary numbers produced and store it into a vector. Is it possible?

I think I have got a solution using bitset, and it works fine.

    std::ostringstream oss;
    int s = 3;
    for (int i = 1; i<s;i++)
    {
        itoa(i,buffer,2);
        oss<<setfill('0')<<setw(3);
        oss<<buffer;

        string s = oss.str();
        cout<<s<<'\n'<<endl;

    };

However, I just want to point out that the solution I obtained looks some this!

Can it manipulated by flushing out streams in consecutive iterations. Its just an afterthought.

Answer 1

Consider using a bitset instead of itoa :

#include <bitset>
#include <iostream>
#include <string>
#include <vector>

int main() {
  std::vector<std::string> binary_representations;

  int s = 8;
  for (int i = 1; i < s; i++)
  {
    binary_representations.push_back(std::bitset<3>(i).to_string());
  }
}

EDIT: If you need a variable length, one possibility is

// Note: it might be better to make x unsigned here.
// What do you expect to happen if x < 0?
std::string binary_string(int x, std::size_t len) {
  std::string result(len, '0');

  for(std::string::reverse_iterator i = result.rbegin(); i != result.rend(); ++i) {
    *i = x % 2 + '0';
    x /= 2;
  }

  return result;
}

and then later

binary_representations.push_back(binary_string(i, 3));