Getting a substring of a `std::string` between two iterators

I have a program that's expected to take as input a few options to specify probabilities in the form (p1, p2, p3, ... ). So the command line usage would literally be: ``` ./myprog -dist (0.20, 0.40, 0.40) ``` I want to parse lists like this in C++ and I am currently trying to do it with iterators for the std::string type and the split function provided by Boost. ``` // Assume stuff up here is OK std::vector<string> dist_strs; // Will hold the stuff that is split by boost. std::string tmp1(argv[k+1]); // Assign the parentheses enclosed list into this std::string. // Do some error checking here to make sure tmp1 is valid. boost::split(dist_strs, <what to put here?> , boost::is_any_of(", ")); ``` Note above the `<what to put here?>` part. Since I need to ignore the beginning and ending parentheses, I want to do something like ``` tmp1.substr( ++tmp1.begin(), --tmp1.end() ) ``` but it doesn't look like `substr` works this way, and I cannot find a function in the documentation that works to do this. One idea I had was to do iterator arithmetic, if this is permitted, and use `substr` to call ``` tmp1.substr( ++tmp1.begin(), (--tmp1.end()) - (++tmp1.begin()) ) ``` but I wasn't sure if this is allowed, or if it is a reasonable way to do it. If this isn't a valid approach, what is a better one? ...Many thanks in advance.