C++ bit string to int conversion

Question

I am trying to convert a bit string (bitString) of length 'sLength' to an int. The following code works fine for me in my computer. Is there any case where it may not work?

int toInt(string bitString, int sLength){

    int tempInt;
    int num=0;
    for(int i=0; i<sLength; i++){
        tempInt=bitString[i]-'0';
        num=num+tempInt * pow(2,(sLength-1-i));
    }

    return num;
}

Thanks in advance

Answer 1

pow works with doubles. Result may be inaccurate. Use bit arithmetic instead

num |= (1 << (sLength-1-i)) * tempInt;

Don't also forget about cases when bitString contains symbols other than '0' and '1' or too long

Answer 2

Or, you can let the standard library do the heavy lifting:

#include <bitset>
#include <string>
#include <sstream>
#include <climits>

// note the result is always unsigned
unsigned long toInt(std::string const &s) {
    static const std::size_t MaxSize = CHAR_BIT*sizeof(unsigned long);
    if (s.size() > MaxSize) return 0; // handle error or just truncate?

    std::bitset<MaxSize> bits;
    std::istringstream is(s);
    is >> bits;
    return bits.to_ulong();
}