How to convert a very big Binary Number(Almost 30,000 digits) in String to a decimal Number in String in C++? [closed]

There is a function int(string, 2) in Python that converts a very big binary string number to a decimal number in string. I want to do a similar thing in C++. Is there any easy way to do it like some built-in function?

Example: Convert "1000" to "8"