Convert binary bitset to hexadecimal (C++)

Question

Is there a simple way to convert a binary bitset to hexadecimal? The function will be used in a CRC class and will only be used for standard output.

I've thought about using to_ulong() to convert the bitset to a integer, then converting the integers 10 - 15 to A - F using a switch case. However, I'm looking for something a little simpler.

I found this code on the internet:

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

using namespace std;
int main(){
    string binary_str("11001111");
    bitset<8> set(binary_str);  
    cout << hex << set.to_ulong() << endl;
}

It works great, but I need to store the output in a variable then return it to the function call rather than send it directly to standard out.

I've tried to alter the code but keep running into errors. Is there a way to change the code to store the hex value in a variable? Or, if there's a better way to do this please let me know.

Thank you.

Answer 1

You can send the output to a std::stringstream, and then return the resultant string to the caller:

stringstream res;
res << hex << uppercase << set.to_ulong();
return res.str();

This would produce a result of type std::string.

Answer 2

Here is an alternative for C:

unsigned int bintohex(char *digits){
  unsigned int res=0;
  while(*digits)
    res = (res<<1)|(*digits++ -'0');
  return res;
}

//...

unsigned int myint=bintohex("11001111");
//store value as an int

printf("%X\n",bintohex("11001111"));
//prints hex formatted output to stdout
//just use sprintf or snprintf similarly to store the hex string