Fast way to convert a binary number to a decimal number

Question

I have to convert a binary number like for example unsigned int bin_number = 10101010 into its decimal representation (i.e. 170) as quickly as possible

Answer 1

Well, if this "number" is actually a string gotten from some source (read from a file or from a user) that you converted into a number (thinking it to be more appropriate for an actual number), which is quite likely, you can use a std::bitset to do the conversion:

#include 

unsigned int number = std::bitset<32>("10101010").to_ulong();

(Of course the 32 here is implementation-defined and might be more appropriately written as std::numeric_limits::digits.)

But if it is really a number (integer variable) in the (very) first place you could do:

#include 

unsigned int number = std::bitset<32>(std::to_string(bin_number)).to_ulong();

(using C++11's to_string) But this will probably not be the most efficient way anymore, as others have presented more efficient algorithms based on numbers. But as said, I doubt that you really get this number as an actual integer variable in the very first place, but rather read it from some text file or from the user.