How to split a binary string of numbers from a file and convert to Hex?

Question

C++ / C#

Hello, there is a file, it contains N number of lines. Each line has a maximum of 250 characters. zeros and ones, no spaces.
It is necessary to extract this string, after which, from its end, translate 4 characters into hexadecimal system.
Example:

100 4
00001  01
011101001010110110000001000 3A56C08

As I understand it, I create a stream through ifstream, get the value into a char variable of size 250, and then it’s more convenient to send it to a function, where the received value must be divided into 4-digit ones, and then after separating the first four, send it to the function with translation in hexadecimal? How can I separate 4 characters from the end?
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UPD
Divided the string, now I get the buff2 variable;
which now, for example, contains 0100.
How can you extract it in binary form?
Required from such a string to one binary value. get HEXIC.
usage

int buff4int = stoi(buff2);
cout << hex << buff4int << endl;

doesn't help because it translates from decimal.
in the answer, 100 is not 4, but 64.

Answer 1

pluses are not my forte.... you don't want to expand your erudition, in another language (with me it means c #) - yes, this will not be a direct solution... but at least it will be "food for thought";))
ps if it is interesting to tumble into the very essence - welcome to the comments