How can I combine multiple char's to make a string?

I am doing string parsing and essentially what I would like to do is something like this:

string signature = char[index+1] + '/' + char[index+2];

BUT you can't do string concatenation on char's so that brings me to this question, how can I simulate concatenation on char's?

I know that the string library in C++ has append but I don't think that works for my case. Any ideas?