c++ - Explaining a string trimming function -

i came across code below need understanding code. assume string s has spaces either side.

string trim(string const& s){    auto front = find_if_not(begin(s), end(s), isspace);    auto = find_if_not(rbegin(s), rend(s), isspace);    return string { front, back.base() }; } 

the author stated points end of last space whereas front points first non-white space character. back.base() called don't understand why.

also curly braces, following string in return statement, represent?

the braces new c++11 initialisation.

.base() , reverse iterators

the .base() the underlying iterator (back reverse_iterator), construct new string valid range.

a picture. normal iterator positions of string (it little more complex regarding how rend() works, conceptually anyway...)

        begin                                 end           v                                    v         -------------------------------------         | sp | sp | | b | c | d | sp | sp |         -------------------------------------       ^                                   ^     rend                                rbegin 

once 2 find loops finish, result of iterators in sequence positioned at:

                  front                     v         -------------------------------------         | sp | sp | | b | c | d | sp | sp |         -------------------------------------                                 ^                               

were take iterators , construct sequence them (which can't, they're not matching types, regardless, supposed could), result "copy starting @ a, stopping @ d" but not include d in resulting data.

enter back() member of reverse iterator. returns non-reverse iterator of forward iterator class, positioned @ element "next to" iterator; i.e.

                  front                     v         -------------------------------------         | sp | sp | | b | c | d | sp | sp |         -------------------------------------                                     ^                                back.base() 

now when copy our range { front, back.base() } copy starting @ a , stopping @ first space (but not including it), thereby including d have missed.

its slick little piece of code, btw.

some additional checking

added basic checks original code.

in trying keeping spirit of original code (c++1y/c++14 usage), adding basic checks empty , white space strings;

string trim_check(string const& s) {   auto is_space = [](char c) { return isspace(c, locale()); };   auto front = find_if_not(begin(s), end(s), is_space);   auto = find_if_not(rbegin(s), make_reverse_iterator(front), is_space);   return string { front, back.base() }; }