Read large Base-10 number of arbitrary size into bitset

Question

I want to read a base10 number from a string or stdin into a bitset. Is there any std function to do this, or do I have to implement it myself?

Example:

bitset<4> buffer;
cin >> buffer;
cout << buffer;

Input: 5

Output: 0101

Note: I need to support any length input, as long as it fits inside the bitset

@Avezan - that reads a base2 string into a bitset, if I'm not mistaken — , Jun 11 '18 at 01:27
Yes base2 from string, but that is not really a trouble, convert string to int and pass to constructor.. — Avezan, Jun 11 '18 at 01:32
@Avezan that is the problem, since the string will be too big to hold by an int — , Jun 11 '18 at 01:34
@Avezan yes (it will be arbirary length but less than 2^(size of bitset)) — , Jun 11 '18 at 01:40

Kostas · Answer 1 · 2018-06-11T04:02:43.613

0

You can simply use the std::bitset constructor:

bitset( unsigned long val );

Note that in the case you do not provide enough bits, the result will keep the least significant N bits.

E.g.

std::bitset<2> set(5);
std::cout << set << std::endl;

01 (instead of 101)

edited Jun 11 '18 at 04:02

answered Jun 11 '18 at 03:54

Kostas

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score 0 · Answer 2 · answered Jun 12 '18 at 06:52

You can use boost multiprecision library to store integer of arbitary size and then process it to produce binary output.

Following is code which use library, convert to hex using std::hex conversion and then reads hex stream and output binary stream. I have overloaded >> for bitset to read big decimal number into bitstream. << outputs correct binary output as expected. you can use any size bitset (in multiple of 4), it should work. Of coarse, error checking has to be done so that it does not cross bitset size. Probably you can start with this version.

#include <boost/multiprecision/cpp_int.hpp>
#include<bitset>
#include<iostream>

using namespace std;


template<int N>
istream& operator >> (istream& in, bitset<N>& b)
{
    using namespace boost::multiprecision;
    cpp_int bigNumber;
    stringstream ss;
    in >> bigNumber; 
    ss << std::hex << bigNumber;


    b.reset();
    int i = 0;
    string s = ss.str();

    for (auto& iter = s.rbegin(); iter != s.rend();  iter++)
    {
        switch (toupper(*iter))
        {
         case '0':
            b[i] = 0; i++;
            b[i] = 0; i++;
            b[i] = 0; i++;
            b[i] = 0; i++;
            break;
        case '1':
            b[i] = 1; i++;
            b[i] = 0; i++;
            b[i] = 0; i++;
            b[i] = 0; i++;
            break;

        case '2':
            b[i] = 0; i++;
            b[i] = 1; i++;
            b[i] = 0; i++;
            b[i] = 0; i++;
            break;

        case '3':
            b[i] = 1; i++;
            b[i] = 1; i++;
            b[i] = 0; i++;
            b[i] = 0; i++;
            break;
        case '4':
            b[i] = 0; i++;
            b[i] = 0; i++;
            b[i] = 1; i++;
            b[i] = 0; i++;
            break;
        case '5':
            b[i] = 1; i++;
            b[i] = 0; i++;
            b[i] = 1; i++;
            b[i] = 0; i++;
            break;
        case '6':
            b[i] = 0; i++;
            b[i] = 1; i++;
            b[i] = 1; i++;
            b[i] = 0; i++;
            break;
        case '7':
            b[i] = 1; i++;
            b[i] = 1; i++;
            b[i] = 1; i++;
            b[i] = 0; i++;
            break;
        case '8':
            b[i] = 0; i++;
            b[i] = 0; i++;
            b[i] = 0; i++;
            b[i] = 1; i++;
            break;
        case '9':
            b[i] = 1; i++;
            b[i] = 0; i++;
            b[i] = 0; i++;
            b[i] = 1; i++;
            break;
        case 'A':
            b[i] = 0; i++;
            b[i] = 1; i++;
            b[i] = 0; i++;
            b[i] = 1; i++;
            break;
        case 'B':
            b[i] = 1; i++;
            b[i] = 1; i++;
            b[i] = 0; i++;
            b[i] = 1; i++;
            break;
        case 'C':
            b[i] = 0; i++;
            b[i] = 0; i++;
            b[i] = 1; i++;
            b[i] = 1; i++;
            break;
        case 'D':
            b[i] = 1; i++;
            b[i] = 0; i++;
            b[i] = 1; i++;
            b[i] = 1; i++;
            break;
        case 'E':
            b[i] = 0; i++;
            b[i] = 1; i++;
            b[i] = 1; i++;
            b[i] = 1; i++;
            break;
        case 'F':
            b[i] = 1; i++;
            b[i] = 1; i++;
            b[i] = 1; i++;
            b[i] = 1; i++;
            break;
        }
    }

    return in;
}

int main()
{

    std::bitset<80> b;

    cin >> b;
    cout << b << endl;

    system("pause");
    return 0;
}

output of program:

9999999999999
00000000000000000000000000000000000010010001100001001110011100101001111111111111
Press any key to continue . . .

Read large Base-10 number of arbitrary size into bitset

2 Answers2