Problem to convert string binary (64 bits) to decimal (c++ in iphone)

Question

Hi I have a problem converting a string binary to a decimal

I was using bitset

bitstring ="1011010001111111";

unsigned long binToDec( string bitstring){
    bitset<32> dec (bitstring);
    return dec.to_ulong();
}

All of this works fine, but !! the problem comes when i try to do the same with a bits string with more of 32 bits. I know that bitset only does the conversion with 4 bytes, but i need to do the conversion with strings that has 48 or 56 bits (sometimes i need to get 14 or 15 digits )

string bitstring;
bitstring ="11100101001001000000100000100100110100110011010001111111";
i want to get this number: 64497387062899840

Any sugestion? anybody have a function to transform a binary string to decimal ?

Note: i can´t use boost because it´s not ported to the iphone.

Thanks for your help

Answer 1

The simplest answer would be to chop your string in half, convert it to a pair of 32bit ints and then pack them together.

Answer 2

This should do the trick, but is untested.

unsigned long binToDec(const std::string& s)
{
  unsigned long d = 0;
  for (int i = 0; i < s.size(); ++i)
  {
    d <<= 1;
    if (s[i] == '1')
      ++d;
  }
  return d;
}

Answer 3

You are probably hitting overflow whenever you cross ULONG_MAX. Use a bigger data type such as unsigned long long. However, if your number can be larger than the max this type can hold, you are probably looking at having to implement a bignum library.

Following cube's suggestion, vanilla C code:

#include <stdio.h>
#include <stdint.h>
#include <inttypes.h> 

uint64_t binToDec(const char * s){
        uint64_t res = 0; size_t i, n;
        for (i = 0, n = strlen(s) - 1; i < n; ++i) {
                 res = (res | (unsigned int)(s[ i ] - '0')) << 1;
        }
        return res;
}

int main() {
   /* Note the special C99 format specifier macros defined in <inttypes.h> */
   printf("%"PRIu64"\n", 
     binToDec("11100101001001000000100000100100110100110011010001111111"));
}

Note: ISO C++ does not support long long.

Answer 4

I've just put together this and it seems to work with your example, I haven't tested any bigger values, compared result with calculator.

Outputs:

64497387062899839

Code:

#include <iostream>
#include <limits>

using namespace std;

unsigned long long convert(string& bits)
{
    if (bits.length() > (size_t)numeric_limits<unsigned long long>::digits)
        return 0;

    unsigned long long sum = 0;
    unsigned long long shift = 1;
    for (string::reverse_iterator it(bits.rbegin()), end(bits.rend());
         it < end; ++it)
    {
        if (*it == '1') sum += shift;
        shift = (shift << 1);
    }

    return sum;
}

int main()
{
    string bits("11100101001001000000100000100100110100110011010001111111");
    cout << "returned: " << convert(bits) << endl;
}