C++ - reproduce trim function [duplicate]

Just asking why I'm not able to delete an interator as the beginning of the string to the end

I tried to do this:
The first called to the erase method work finely but not the second, why ?

int main() { std :: string str{" Supprimer les espaces a la fin et au debut "}; std :: string :: const_iterator itStart{ std :: find_if_not(std :: cbegin(str), std :: cend(str), isspace) }; std :: string :: const_reverse_iterator itEnd{ std :: find_if_not(std :: crbegin(str), std :: crend(str), isspace) }; std :: cout << *itStart << std :: endl; std :: cout << *itEnd << std :: endl; str.erase(std :: cbegin(str), itStart); str.erase(itEnd, std :: end(str)); std :: cout << str << "|" << std :: endl; return 0; }